Infrared and Raman Spectroscopy: Principles and Spectral Interpretation/Peter Larkin

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INFRARED AND RAMAN SPECTROSCOPY PRINCIPLES AND SPECTRAL INTERPRETATION

PETER LARKIN

AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Elsevier 225 Wyman Street, Waltham, MA 02451, USA 525 B Street, Suite 1900, San Diego, CA 92101-4495, USA The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, UK Radarweg 29, PO Box 211, 1000 AE Amsterdam, The Netherlands Copyright Ó 2011 Elsevier Inc. All rights reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email: [email protected]. Alternatively you can submit your request online by visiting the Elsevier web site at http://elsevier. com/locate/permissions, and selecting Obtaining permission to use Elsevier material Notice No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein Library of Congress Cataloging-in-Publication Data Larkin, Peter (Peter J.) Infrared and raman spectroscopy: principles and spectral interpretation/Peter Larkin. p. cm. ISBN: 978-0-12-386984-5 (hardback) 1. Infrared spectroscopy. 2. Raman Spectroscopy. I. Title. QD96.I5L37 2011 535’.8’42ddc22 2011008524 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library

ISBN: 978-0-12-386984-5

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Preface

IR and Raman spectroscopy have tremendous potential to solve a wide variety of complex problems. Both techniques are completely complementary providing characteristic fundamental vibrations that are extensively used for the determination and identification of molecular structure. The advent of new technologies has introduced a wide variety of options for implementing IR and Raman spectroscopy into the hands of both the specialist and the non- specialist alike. However, the successful application of both techniques has been limited since the acquisition of high level IR and Raman interpretation skills is not widespread among potential users. The full benefit of IR and Raman spectroscopy cannot be realized without an analyst with basic knowledge of spectral interpretation. This book is a response to the recent rapid growth of the field of vibrational spectroscopy. This has resulted in a corresponding need to educate new users on the value of both IR and Raman spectral interpretation skills. To begin with, the end user must have a suitable knowledge base of the instrument and its capabilities. Furthermore, he must develop an understanding of the sampling options and limitations, available software tools, and a fundamental understanding of important characteristic group frequencies for both IR and Raman spectroscopy. A critical skill set an analyst may require to solve a wide variety of chemical questions and problems using vibrational spectroscopy is depicted in Figure 1 below. Selecting the optimal spectroscopic technique to solve complex chemical problems encountered by the analyst requires the user to develop a skill set outlined in Figure 1. A knowledge of spectral interpretation enables the user to select the technique with the most favorable selection

Software knowledge Instrument Chemometric capability models

Instrument Spectral Spectroscopist accessories interpretation

Sampling Method options validation Method development

FIGURE 1 Skills required for a successful vibrational spectroscopist. (Adapted from R.D. McDowall, Spectroscopy Application Notebook, February 2010).

ix x PREFACE of characteristic group frequencies, optimize the sample options (including accessories if necessary), and use suitable software tools (both instrumental and chemometric), to provide a robust, sensitive analysis that is easily validated. In this book we provide a suitable level of information to understand instrument capabilities, sample presentation, and selection of various accessories. The main thrust of this text is to develop high level of spectral interpretation skills. A broad understanding of the bands associated with functional groups for both IR and Raman spectroscopy is the basic spectroscopy necessary to make the most of the potential and set realistic expectations for vibrational spectroscopy applications in both academic and industrial settings. A primary goal of this book has been to fully integrate the use of both IR and Raman spectroscopy as spectral interpretation tools. To this end we have integrated the discussion of IR and Raman group frequencies into different classes of organic groups. This is supplemented with paired generalized IR and Raman spectra, use of numerous tables that are discussed in text, and finally referenced to a selection of fully interpreted IR and Raman spectra. This fully integrated approach to IR and Raman interpretation enables the user to utilize the strengths of both techniques while also recognizing their weaknesses. We have attempted to provide an integrated approach to the important group frequency of both infrared and Raman spectroscopy. Graphics is used extensively to describe the basic principles of vibrational spectroscopy and the origins of group frequencies. The book includes sections on basic principles in Chapters 1 and 2; instrumentation, sampling methods, and quantitative analysis in Chapter 3; a discussion of important environmental effects in Chapter 4; and a discussion of the origin of group frequencies in Chapter 5. Chap- ters 4 and 5 provide the essential background to understand the origin of group frequencies in order to assign them in a spectra and to explain why group frequencies may shift. Selected problems are included at the end of some of these chapters to help highlight important points. Chapters 6 and 7 provide a highly detailed description of important characteristic group frequencies and strategies for interpretation of IR and Raman spectra. Chapter 8 is the culmination of the book and provides 110 fully interpreted paired IR and Raman spectra arranged in groups. The selected compounds are not intended to provide a comprehensive spectral library but rather to provide a significant selection of interpreted examples of functional group frequencies. This resource of interpreted IR and Raman spectra should be used to help verify proposed assignments that the user will encounter. The final chapter is comprised of the paired IR and Raman spectra of 44 different unknown spectra with a corresponding answer key.

Peter Larkin Connecticut, August 2010 CHAPTER 1

Introduction: Infrared and Raman Spectroscopy

Vibrational spectroscopy includes several different techniques, the most important of which are mid-infrared (IR), near-IR, and Raman spectroscopy. Both mid-IR and Raman spectroscopy provide characteristic fundamental vibrations that are employed for the elucidation of molecular structure and are the topic of this chapter. Near-IR spectroscopy measures the broad overtone and combination bands of some of the fundamental vibrations (only the higher frequency modes) and is an excellent technique for rapid, accurate quantitation. All three techniques have various advantages and disadvantages with respect to instrumentation, sample handling, and applications. Vibrational spectroscopy is used to study a very wide range of sample types and can be carried out from a simple identification test to an in-depth, full spectrum, qualitative and quantitative analysis. Samples may be examined either in bulk or in microscopic amounts over a wide range of temperatures and physical states (e.g., gases, liquids, latexes, powders, films, fibers, or as a surface or embedded layer). Vibrational spectroscopy has a very broad range of applications and provides solutions to a host of important and challenging analytical problems. Raman and mid-IR spectroscopy are complementary techniques and usually both are required to completely measure the vibrational modes of a molecule. Although some vibrations may be active in both Raman and IR, these two forms of spectroscopy arise from different processes and different selection rules. In general, Raman spectroscopy is best at symmetric vibrations of non-polar groups while IR spectroscopy is best at the asymmetric vibrations of polar groups. Table 1.1 briefly summarizes some of the differences between the techniques. Infrared and Raman spectroscopy involve the study of the interaction of radiation with molecular vibrations but differs in the manner in which photon energy is transferred to the molecule by changing its vibrational state. IR spectroscopy measures transitions between molecular vibrational energy levels as a result of the absorption of mid-IR radiation. This interaction between light and matter is a resonance condition involving the electric dipole- mediated transition between vibrational energy levels. Raman spectroscopy is a two-photon inelastic light-scattering event. Here, the incident photon is of much greater energy than the vibrational quantum energy, and loses part of its energy to the molecular vibration with the

1 2 1. INTRODUCTION: INFRARED AND RAMAN SPECTROSCOPY

TABLE 1.1 Comparison of Raman, Mid-IR and Near-IR Spectroscopy

Raman Infrared Near-IR

Ease of sample Very simple Variable Simple preparation Liquids Very simple Very simple Very simple Powders Very simple Simple Simple

Polymers Very simple* Simple Simple Gases Simple Very simple Simple Fingerprinting Excellent Excellent Very good Best vibrations Symmetric Asymmetric Comb/overtone Group Frequencies Excellent Excellent Fair Aqueous solutions Very good Very difﬁcult Fair

Quantitative analysis Good Good Excellent Low frequency modes Excellent Difﬁcult No

* True for FT-Raman at 1064 nm excitation.

remaining energy scattered as a photon with reduced frequency. In the case of Raman spectroscopy, the interaction between light and matter is an off-resonance condition involving the Raman polarizability of the molecule. The IR and Raman vibrational bands are characterized by their frequency (energy), intensity (polar character or polarizability), and band shape (environment of bonds). Since the vibrational energy levels are unique to each molecule, the IR and Raman spectrum provide a “fingerprint” of a particular molecule. The frequencies of these molecular vibrations depend on the masses of the atoms, their geometric arrangement, and the strength of their chemical bonds. The spectra provide information on molecular structure, dynamics, and environment. Two different approaches are used for the interpretation of vibrational spectroscopy and elucidation of molecular structure. 1) Use of group theory with mathematical calculations of the forms and frequencies of the molecular vibrations. 2) Use of empirical characteristic frequencies for chemical functional groups. Many empirical group frequencies have been explained and refined using the mathematical theoretical approach (which also increases reliability). In general, many identification problems are solved using the empirical approach. Certain functional groups show characteristic vibrations in which only the atoms in that particular group are displaced. Since these vibrations are mechanically independent from the rest of the molecule, these group vibrations will have a characteristic frequency, which remains relatively unchanged regardless of what molecule the group is in. Typically, group frequency HISTORICAL PERSPECTIVE: IR AND RAMAN SPECTROSCOPY 3

OH str C O C C=O CH2 =CH alcohols X=Y=Z ethers or X≡Y acid CH3 aromatic phenols ester salt, C=N esters C Cl NH str N=C=O, ketone 2 - C OH C Br C≡N amines amide alcohols aliphatic CH str amides P OH or SH str phenols Intensity S=O def, R CO

2 P=O

C=C olefinic, aromatic C=C olefinic, NH C F =CH and aromatic CH str

3000 2000 1500 1000 500 Wavenumbers(cm–1)

FIGURE 1.1 Regions of the fundamental vibrational spectrum with some characteristic group frequencies.

analysis is used to reveal the presence and absence of various functional groups in the molecule, thereby helping to elucidate the molecular structure. The vibrational spectrum may be divided into typical regions shown in Fig. 1.1. These regions can be roughly divided as follows: • XeH stretch (str) highest frequencies (3700e2500 cm 1) • XhY stretch, and cumulated double bonds X¼Y¼Z asymmetric stretch (2500e2000 cm 1) • X¼Y stretch (2000e1500 cm 1) • XeH deformation (def) (1500e1000 cm 1) • XeY stretch (1300e600 cm 1) The above represents vibrations as simple, uncoupled oscillators (with the exception of the cumulated double bonds). The actual vibrations of molecules are often more complex and as we will see later, typically involve coupled vibrations.

1. HISTORICAL PERSPECTIVE: IR AND RAMAN SPECTROSCOPY

IR spectroscopy was the ﬁrst structural spectroscopic technique widely used by organic chemists. In the 1930s and 1940s both IR and Raman techniques were experimentally challenging with only a few users. However, with conceptual and experimental advances, IR gradually became a more widely used technique. Important early work developing IR spectroscopy occurred in industry as well as academia. Early work using vibrating mechanical molecular models were employed to demonstrate the normal modes of vibration in various molecules.1, 2 Here the nuclei were represented by steel balls and the interatomic bonds by helical springs. A ball and spring molecular model would be suspended by long threads attached to each ball enabling studies of planar vibrations. The source of oscillation for the ball and spring model was through coupling to an eccentric variable speed motor which enabled studies of the internal vibrations of molecules. When the oscillating frequency matched that of one of the natural frequencies of vibration for the mechanical model 4 1. INTRODUCTION: INFRARED AND RAMAN SPECTROSCOPY

3400 3300 3200 3100 3000 2900 2800 2700

CH3, CH2, CH, stretch C≡C H

Arom-H

C=CH2

C=CH

R CH3

Arom-CH3

R CH2 R

R O CH3

R2 N CH3

O=C H

FIGURE 1.2 The correlation chart for CH3,CH2, and CH stretch IR bands.

a resonance occurred and the model responded by exhibiting one of the internal vibrations of the molecule (i.e. normal mode). In the 1940s both Dow Chemical and American Cyanamid companies built their own NaCl prism-based, single beam, meter focal length instruments primarily to study hydrocarbons. The development of commercially available IR instruments had its start in 1946 with Amer- ican Cyanamid Stamford laboratories contracting with a small optical company called PerkineElmer (PE). The Stamford design produced by PE was a short focal length prism IR spectrometer. With the commercial availability of instrumentation, the technique then beneﬁted from the conceptual idea of a correlation chart of important bands that concisely summarize where various functional groups can be expected to absorb. This introduction of the correlation chart enabled chemists to use the IR spectrum to determine the structure.3, 4 The explosive growth of IR spectroscopy in the 1950s and 1960s were a result of the development of commercially available instrumentation as well as the conceptual breakthrough of a correlation chart. Appendix shows IR group frequency correlation charts for a variety of important functional groups. Shown in Fig. 1.2 is the correlation chart for CH3,CH2, and CH stretch IR bands. The subsequent development of double beam IR instrumentation and IR correlation charts resulted in widespread use of IR spectroscopy as a structural technique. An extensive user base resulted in a great increase in available IR interpretation tools and the eventual development of FT-IR instrumentation. More recently, Raman spectroscopy has beneﬁted from dramatic improvements in instrumentation and is becoming much more widely used than in the past. HISTORICAL PERSPECTIVE: IR AND RAMAN SPECTROSCOPY 5 References

1. Kettering, C. F.; Shultz, L. W.; Andrews, D. H. Phys. Rev. 1930, 36, 531. 2. Colthup, N. B. J. Chem. Educ. 1961, 38 (8), 394e396. 3. Colthup, N. B. J. Opt. Soc. Am. 1950, 40 (6), 397e400. 4. Infrared Characteristic Group Frequencies G. Socrates, 2nd ed.; John Wiley: New York, NY, 1994.

CHAPTER 2

Basic Principles

1. ELECTROMAGNETIC RADIATION

All light (including infrared) is classified as electromagnetic radiation and consists of alter- nating electric and magnetic fields and is described classically by a continuous sinusoidal wave like motion of the electric and magnetic fields. Typically, for IR and Raman spectroscopy we will only consider the electric field and neglect the magnetic field component. Figure 2.1 depicts the electric field amplitude of light as a function of time. The important parameters are the wavelength (l, length of 1 wave), frequency (v, number cycles per unit time), and wavenumbers (n, number of waves per unit length) and are related to one another by the following expression: n 1 n ¼ ¼ ðc=nÞ l where c is the speed of light and n the refractive index of the medium it is passing through. In quantum theory, radiation is emitted from a source in discrete units called photons where the v E photon frequency, , and photon energy, p, are related by

Ep ¼ hn

where h is Planck’s constant (6.6256 10 27 erg sec). Photons of speciﬁc energy may be absorbed (or emitted) by a molecule resulting in a transfer of energy. In absorption spectroscopy this will result in raising the energy of molecule from ground to a speciﬁc excited state

E + + – –

Time

FIGURE 2.1 The amplitude of the electric vector of electromagnetic radiation as a function of time. The wavelength is the distance between two crests.

7 8 2. BASIC PRINCIPLES

E 2

Molecular E energy p ( ) levels E E E p = 2 – 1 E 1

FIGURE 2.2 Absorption of electromagnetic radiation.

E E E as shown in Fig. 2.2. Typically the rotational ( rot), vibrational ( vib), or electronic ( el) energy of molecule is changed by 6E:

DE ¼ Ep ¼ hn ¼ hcn In the absorption of a photon the energy of the molecule increases and DE is positive. To a ﬁrst approximation, the rotational, vibrational, and electronic energies are additive: E ¼ E þ E þ E T el vib rot E We are concerned with photons of such energy that we consider vib alone and only for E condensed phase measurements. Higher energy light results in electronic transitions ( el) E and lower energy light results in rotational transitions ( rot). However, in the gas-state E þ E both IR and Raman measurements will include vib rot.

2. MOLECULAR MOTION/DEGREES OF FREEDOM

2.1. Internal Degrees of Freedom

The molecular motion that results from characteristic vibrations of molecules is described by the internal degrees of freedom resulting in the well-known 3n 6 and 3n 5 rule-of-thumb for vibrations for non-linear and linear molecules, respectively. Figure 2.3 shows the fundamental vibrations for the simple water (non-linear) and carbon dioxide (linear) molecules. The internal degrees of freedom for a molecule deﬁne n as the number of atoms in a molecule and deﬁne each atom with 3 degrees of freedom of motion in the X, Y, and Z directions resulting in 3n degrees of motional freedom. Here, three of these degrees are translation, while three describe rotations. The remaining 3n 6 degrees (non-linear molecule) are motions, which change the distance between atoms, or the angle between bonds. A simple ¼ example of the 3n 6 non-linear molecule is water (H2O) which has 3(3) 6 3 degrees of freedom. The three vibrations include an in-phase and out-of-phase stretch and a deforma- n tion (bending) vibration. Simple examples of 3 5 linear molecules include H2,N2, and O2 which all have 3(2) 5 ¼ 1 degree of freedom. The only vibration for these simple molecules ¼ is a simple stretching vibration. The more complicated CO2 molecule has 3(3) 5 4 degrees of freedom and therefore four vibrations. The four vibrations include an in-phase and out- of-phase stretch and two mutually perpendicular deformation (bending) vibrations. The molecular vibrations for water and carbon dioxide as shown in Fig. 2.3 are the normal mode of vibrations. For these vibrations, the Cartesian displacements of each atom in molecule MOLECULAR MOTION/DEGREES OF FREEDOM 9

(a) Water O O O

H H H HHH ν ν ν op ip def

(b) CO2

O C O O C O O C O O C O ν ν ν ip def ν op def

FIGURE 2.3 Molecular motions which change distance between atoms for water and CO2. change periodically with the same frequency and go through equilibrium positions simultaneously. The center of the mass does not move and the molecule does not rotate. Thus in the case of harmonic oscillator, the Cartesian coordinate displacements of each atom plotted as a function of time is a sinusoidal wave. The relative vibrational amplitudes may differ in either magnitude or direction. Figure 2.4 shows the normal mode of vibration for a simple diatomic such as HCl and a more complex totally symmetric CH stretch of benzene.

(a) Diatomic Stretch

Equilibrium position of Displacement atoms

Time

(b) Totally symmetric CH stretch of benzene

FIGURE 2.4 Normal mode of vibration for a simple diatomic such as HCl (a) and a more complex species such as benzene (b). The displacement versus time is sinusoidal, with equal frequency for all the atoms. The typical Cartesian displacement vectors are shown for the more complicated totally symmetric CH stretch of benzene. 10 2. BASIC PRINCIPLES 3. CLASSICAL HARMONIC OSCILLATOR

To better understand the molecular vibrations responsible for the characteristic bands observed in infrared and Raman spectra it is useful to consider a simple model derived 1 m from classical mechanics. Figure 2.5 depicts a diatomic molecule with two masses 1 and m 2 connected by a massless spring. The displacement of each mass from equilibrium along X X the spring axis is 1 and 2. The displacement of the two masses as a function of time for a harmonic oscillator varies periodically as a sine (or cosine) function. In the above diatomic system, although each mass oscillates along the axis with different amplitudes, both atoms share the same frequency and both masses go through their equilibrium positions simultaneously. The observed amplitudes are inversely proportional to the mass of the atoms which keeps the center of mass stationary X m 1 ¼ 2 X2 m1

The classical vibrational frequency for as diatomicffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi molecule is: 1 1 1 n ¼ Kð þ Þ 2p m1 m2 K m m n where is the force constant in dynes/cm and 1 and 2 are the masses in grams and is in cycles per second. This expression is also encountered using the reduced mass where 1 1 1 m1m2 ¼ þ or m ¼ m m1 m2 m1 þ m2 In vibrational spectroscopy wavenumber units, n (waves per unit length) are more typically used m K m 1 2

X X – 2 1

Time

Displacement

FIGURE 2.5 K m m X Motion of a simple diatomic molecule. The spring constant is , the masses are 1 and 2, and 1 and X 2 are the displacement vectors of each mass from equilibrium where the oscillator is assumed to be harmonic. CLASSICAL HARMONIC OSCILLATOR 11 sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 1 1 n ¼ K þ 2pc m1 m2 where n is in waves per centimeter and is sometimes called the frequency in cm 1 and c is the speed of light in cm/s. If the masses are expressed in unified atomic mass units (u) and the force constant is expressed in millidynes/A˚ ngstro¨m then: sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 1 n ¼ 1303 K þ m1 m2 ¼ N 5 1/2 pc N 23 1 where 1303 [ a 10 ) /2 and a is Avogadro’s number (6.023 10 mole ) This simple expression shows that the observed frequency of a diatomic oscillator is a function of 1. the force constant K, which is a function of the bond energy of a two atom bond (see Table 2.1) 2. the atomic masses of the two atoms involved in the vibration. TABLE 2.1 Approximate Range of Force Constants for Single, Double, and Triple Bonds

Bond type K (millidynes/A˚ ngstro¨m)

Single 3e6 Double 10e12 Triple 15e18

Table 2.1 shows the approximate range of the force constants for single, double, and triple bonds. Conversely, knowledge of the masses and frequency allows calculation of a diatomic force constant. For larger molecules the nature of the vibration can be quite complex and for more accurate calculations the harmonic oscillator assumption for a diatomic will not be appropriate. The general wavenumber regions for various diatomic oscillator groups are shown in Table 2.2, where Z is an atom such as carbon, oxygen, nitrogen, sulfur, and phosphorus.

TABLE 2.2 General Wavenumber Regions for Various Simple Diatonic Oscillator Groups

L Diatomic oscillator Region (cm 1)

ZeH 4000e2000 ChC, ChN 2300e2000

C¼O, C¼N, C ¼C 1950e1550 CeO, CeN, CeC 1300e800 CeCl 830e560 12 2. BASIC PRINCIPLES 4. QUANTUM MECHANICAL HARMONIC OSCILLATOR

Vibrational spectroscopy relies heavily on the theoretical insight provided by quantum theory. However, given the numerous excellent texts discussing this topic only a very cursory review is presented here. For a more detailed review of the quantum mechanical principles relevant to vibrational spectroscopy the reader is referred elsewhere.2-5 For the classical harmonic oscillation of a diatomic the potential energy (PE) is given by 1 ¼ KX2 PE 2 A plot of the potential energy of this diatomic system as a function of the distance, X between the masses, is thus a parabola that is symmetric about the equilibrium internu- X X K clear distance, e. Here e is at the energy minimum and the force constant, is a measure X of the curvature of the potential well near e. From quantum mechanics we know that molecules can only exist in quantized energy states. Thus, vibrational energy is not continuously variable but rather can only have certain discrete values. Under certain conditions a molecule can transit from one energy state to another (Dy ¼1) which is what is probed by spectroscopy. Figure 2.6 shows the vibrational levels in a potential energy diagram for the quantum mechanical harmonic oscillator. In the case of the harmonic potential these states are equidis- tant and have energy levels E given by 1 E ¼ y þ hv y ¼ 0; 1; 2. i i 2 i

Here, n is the classical vibrational frequency of the oscillator and y is a quantum number which can have only integer values. This can only change by Dy ¼1 in a harmonic oscillator model. The so-called zero point energy occurs when y ¼ 0 where E ¼ ½ hn and this vibrational energy cannot be removed from the molecule.

Probability

= 2 E = 1

= 0

X e X

E = ( i = 1/2) h c υ o Δυ = ± 1

FIGURE 2.6 Potential energy, E, versus internuclear distance, X, for a diatomic harmonic oscillator. IR ABSORPTION PROCESS 13

Anharmonic oscillator Harmonic oscillator E )

D D o e

Potential energy ( = 0 i 1/2 h ν

Internuclear distance (X)

FIGURE 2.7 The potential energy diagram comparison of the anharmonic and the harmonic oscillator. y ¼ D Transitions originate from the 0 level, and o is the energy necessary to break the bond.

Figure 2.6 shows the curved potential wells for a harmonic oscillator with the probability functions for the internuclear distance X, within each energy level. These must be expressed as a probability of finding a particle at a given position since by quantum mechanics we cannot be certain of the position of the mass during the vibration (a consequence of Heisenberg’s uncertainty principle). Although we have only considered a harmonic oscillator, a more realistic approach is to introduce anharmonicity. Anharmonicity results if the change in the dipole moment is not linearly proportional to the nuclear displacement coordinate. Figure 2.7 shows the potential energy level diagram for a diatomic harmonic and anharmonic oscillator. Some of the features introduced by an anharmonic oscillator include the following. The anharmonic oscillator provides a more realistic model where the deviation from harmonic oscillation becomes greater as the vibrational quantum number increases. The separation between adjacent levels becomes smaller at higher vibrational levels until finally the dissociation limit is reached. In the case of the harmonic oscillator only transitions to adjacent levels or so-called fundamental transitions are allowed (i.e., 6y ¼1) while for the anharmonic oscillator, overtones (6y ¼2) and combination bands can also result. Transi- tions to higher vibrational states are far less probable than the fundamentals and are of much weaker intensity. The energy term corrected for anharmonicity is 1 1 2 E ¼ hn y þ hc n y þ y e 2 e e 2 c n where e e defines the magnitude of the anharmonicity.

5. IR ABSORPTION PROCESS

The typical IR spectrometer broad band source emits all IR frequencies of interest simultaneously where the near-IR region is 14,000e4000 cm 1, the mid-IR region is 14 2. BASIC PRINCIPLES

4000e400 cm 1, and the far-IR region is 400e10 cm 1. Typical of an absorption spectroscopy, the relationship between the intensities of the incident and transmitted IR radiation and the analyte concentration is governed by the LamberteBeer law. The IR spectrum is obtained by plotting the intensity (absorbance or transmittance) versus the wavenumber, which is proportional to the energy difference between the ground and the excited vibrational states. Two important components to the IR absorption process are the radiation frequency and the molecular dipole moment. The interaction of the radiation with molecules can be described in terms of a resonance condition where the speciﬁc oscillating radiation frequency matches the natural frequency of a particular normal mode of vibration. In order for energy to be transferred from the IR photon to the molecule via absorption, the molecular vibration must cause a change in the dipole moment of the molecule. This is the familiar selection rule for IR spectroscopy, which requires a change in the dipole moment during the vibration to be IR active. The dipole moment, m, for a molecule is a function of the magnitude of the atomic charges e r ( i) and their positions ( i) X m ¼ e r i i The dipole moments of uncharged molecules derive from partial charges on the atoms, which can be determined from molecular orbital calculations. As a simple approximation, the partial charges can be estimated by comparison of the electronegativities of the atoms. no Homonuclear diatomic molecules such as H2,N2, and O2 have dipole moment and are IR inactive (but Raman active) while heteronuclear diatomic molecules such as HCl, NO, and CO do have dipole moments and have IR active vibrations. The IR absorption process involves absorption of energy by the molecule if the vibration causes a change in the dipole moment, resulting in a change in the vibrational energy level. Figure 2.8 shows the oscillating electric ﬁeld of the IR radiation generates forces on the

Time

++ +++

Forces generated by the photon Dipole electric field

––– ––

One photon cycle

FIGURE 2.8 The oscillating electric field of the photon generates oscillating, oppositely directed forces on the positive and negative charges of the molecular dipole. The dipole spacing oscillates with the same frequency as the incident photon. THE RAMAN SCATTERING PROCESS 15 molecular dipole where the oscillating electric field drives the oscillation of the molecular dipole moment and alternately increases and decreases the dipole spacing. Here, the electric field is considered to be uniform over the whole molecule since l is much greater than the size of most molecules. In terms of quantum mechanics, the IR absorption is an electric dipole operator mediated transition where the change in the dipole moment, m, with respect to a change in the vibrational amplitude, Q, is greater than zero. vm s0 vQ 0 The measured IR band intensity is proportional to the square of the change in the dipole moment.

6. THE RAMAN SCATTERING PROCESS

Light scattering phenomena may be classically described in terms of electromagnetic (EM) radiation produced by oscillating dipoles induced in the molecule by the EM fields of the incident radiation. The light scattered photons include mostly the dominant Rayleigh and the very small amount of Raman scattered light.6 The induced dipole moment occurs as a result of the molecular polarizability a, where the polarizability is the deformability of the electron cloud about the molecule by an external electric field. Figure 2.9 shows the response of a non-polar diatomic placed in an oscillating electric field. Here we represent the static electric field by the plates of a charged capacitor. The negatively charged plate attracts the nuclei, while the positively charged plate attracts the least tightly

Time Electron and proton center Photon electric in homogeneous field diatomic molecule + – –

= = + = + = + – –

Forces on Induced dipole moment Dipole charges induced Field resulting from electron induced by the external turned displacement by charged photon field off capacitor plates

FIGURE 2.9 Induced dipole moment of a homonuclear diatomic originating from the oscillating electric field of the incident radiation. The field relative to the proton center displaces the electron center. The charged plates of a capacitor, which induces a dipole moment in the polarizable electron cloud, can represent the electric field. 16 2. BASIC PRINCIPLES

Wavelength (nm) 1042 1064 1087

Rayleigh Scattering hc ν Anti-Stokes Raman Stokes Scattering Raman Scattering hc (ν + ν ) L m hc ν ν ( L – m) Energy 1 1 0 0 Intensity

200 100 0 –100 –200 ν ν ( L + m)

FIGURE 2.10 Schematic illustration of Rayleigh scattering as well as Stokes and anti-Stokes Raman scattering. n The laser excitation frequency ( L) is represented by the upward arrows and is much higher in energy than the molecular vibrations. The frequency of the scattered photon (downward arrows) is unchanged in Rayleigh scattering but is of either lower or higher frequency in Raman scattering. The dashed lines indicate the “virtual state.” bound outer electrons resulting in an induced dipole moment. This induced dipole moment is an off-resonance interaction mediated by an oscillating electric ﬁeld. In a typical Raman experiment, a laser is used to irradiate the sample with monochromatic radiation. Laser sources are available for excitation in the UV, visible, and near-IR spectral region (785 and 1064 nm). Thus, if visible excitation is used, the Raman scattered light will also be in the visible region. The Rayleigh and Raman processes are depicted in Fig. 2.10. No energy is lost for the elastically scattered Rayleigh light while the Raman scattered photons lose some energy relative to the exciting energy to the speciﬁc vibrational coordinates of the sample. In order for Raman bands to be observed, the molecular vibration must cause a change in the polarizability. Both Rayleigh and Raman are two photon processes involving scattering of incident light ðhcn Þ L , from a “virtual state.” The incident photon is momentarily absorbed by a transition from the ground state into a virtual state and a new photon is created and scattered by a transition from this virtual state. Rayleigh scattering is the most probable event and the scattered intensity is ca. 10 3 less than that of the original incident radiation. This scattered photon results from a transition from the virtual state back to the ground state and is an elastic scattering of a photon resulting in no change in energy (i.e., occurs at the laser frequency). CLASSICAL DESCRIPTION OF THE RAMAN EFFECT 17

Raman scattering is far less probable than Rayleigh scattering with an observed intensity that is ca. 10 6 that of the incident light for strong Raman scattering. This scattered photon results from a transition from the virtual state to the ﬁrst excited state of the molecular vibration. This is described as an inelastic collision between photon and molecule, since the molecule acquires different vibrational energy ðnmÞ and the scattered photon now has different energy and frequency. As shown in Fig. 2.10 two types of Raman scattering exist: Stokes and anti-Stokes. Mole- cules initially in the ground vibrational state give rise to Stokes Raman scattering hcðn n Þ L m while molecules initially in vibrational excited state give rise to anti-Stokes hcðn þ n Þ Raman scattering, L m . The intensity ratio of the Stokes relative to the anti-Stokes Raman bands is governed by the absolute temperature of the sample, and the energy difference between the ground and excited vibrational states. At thermal equilibrium Boltzmann’s law describes the ratio of Stokes relative to anti-Stokes Raman lines. The Stokes Raman lines are much more intense than anti-Stokes since at ambient temperature most molecules are found in the ground state. I The intensity of the Raman scattered radiation R is given by: va 2 I fn4I N R o vQ I N where o is the incident laser intensity, is the number of scattering molecules in a given state, n is the frequency of the exciting laser, a is the polarizability of the molecules, and Q is the vibrational amplitude. The above expression indicates that the Raman signal has several important parameters for Raman spectroscopy. First, since the signal is concentration dependent, quantitation is possible. Secondly, using shorter wavelength excitation or increasing the laser ﬂux power density can increase the Raman intensity. Lastly, only molecular vibrations which cause a change in polarizability are Raman active. Here the change in the polarizability with respect to a change in the vibrational amplitute, Q, is greater than zero. va s0 vQ

The Raman intensity is proportional to the square of the above quantity.

7. CLASSICAL DESCRIPTION OF THE RAMAN EFFECT

The most basic description of Raman spectroscopy describes the nature of the interaction of an oscillating electric field using classical arguments.6 Figure 2.11 schematically represents this basic mathematical description of the Raman effect. As discussed above, the electromagnetic field will perturb the charged particles of the molecule resulting in an induced dipole moment: m ¼ aE where a is the polarizability, E is the incident electric field, and m is the induced dipole moment. Both E and a can vary with time. The electric field of the radiation is oscillating 18 2. BASIC PRINCIPLES

ν (a) (b) (c) (d) o

Rayleigh

ν + ν o m Raman anti-Stokes

ν – ν ν ν ν ± o m o m o νm Raman Stokes

FIGURE 2.11 Schematic representing Rayleigh and Raman scattering. In (a) the incident radiation makes the induced dipole moment of the molecule oscillate at the photon frequency. In (b) the molecular vibration can change the polarizability, a, which changes the amplitude of the dipole moment oscillation. The result as shown in (c) is an amplitude modulated dipole moment oscillation. The image (d) shows the components with steady amplitudes which can emit electromagnetic radiation.

n m as a function of time at a frequency 0, which can induce an oscillation of the dipole moment of the molecule at this same frequency, as shown in Fig. 2.11a. The polarizability a of the molecule has a certain magnitude whose value can vary slightly with time at the much n slower molecular vibrational frequency m, as shown in Fig. 2.11b. The result is seen in Fig. 2.11c, which depicts an amplitude modulation of the dipole moment oscillation of the molecule. This type of modulated wave can be resolved mathematically into three steady n n þ n n n amplitude components with frequencies 0, 0 m, and 0 m as shown in Fig. 2.11d. These dipole moment oscillations of the molecule can emit scattered radiation with these same frequencies called Rayleigh, Raman anti-Stokes, and Raman Stokes frequencies. If a molecular vibration did not cause a variation in the polarizability, then there would be no amplitude modulation of the dipole moment oscillation and there would be no Raman Stokes or anti-Stokes emission.

8. SYMMETRY: IR AND RAMAN ACTIVE VIBRATIONS

The symmetry of a molecule, or the lack of it, will define what vibrations are Raman and IR active.5 In general, symmetric or in-phase vibrations and non-polar groups are most easily studied by Raman while asymmetric or out-of-phase vibrations and polar groups are most easily studied by IR. The classification of a molecule by its symmetry enables understanding of the relationship between the molecular structure and the vibrational spectrum. Symmetry elements include planes of symmetry, axes of symmetry, and a center of symmetry. Group Theory is the mathematical discipline, which applies symmetry concepts to vibrational spectroscopy and predicts which vibrations will be IR and Raman active.1,5 The symmetry elements possessed by the molecule allow it to be classified by a point group and vibrational analysis can be applied to individual molecules. A thorough discussion of Group Theory is beyond the scope of this work and interested readers should examine texts dedicated to this topic.7 SYMMETRY: IR AND RAMAN ACTIVE VIBRATIONS 19

Totally symmetric Asymmetric Center of symmetry vibration vibration

H H H H

O C O O C O O C O

Raman active IR active

FIGURE 2.12 The center of symmetry for H2,CO2, and benzene. The Raman active symmetric stretching vibrations above are symmetric with respect to the center of symmetry. Some IR active asymmetric stretching vibrations are also shown.

For small molecules, the IR and Raman activities may often be determined by a simple inspection of the form of the vibrations. For molecules that have a center of symmetry, the rule of mutual exclusion states that no vibration can be active in both the IR and Raman spectra. For such highly symmetrical molecules vibrations which are Raman active are IR inactive and vice versa and some vibrations may be both IR and Raman inactive. Figure 2.12 shows some examples of molecules with this important symmetry element, the center of symmetry. To deﬁne a center of symmetry simply start at any atom, go in a straight line through the center and an equal distance beyond to ﬁnd another, identical atom. In such cases the molecule has no permanent dipole moment. Examples shown below include H2, CO2, and benzene and the rule of mutual exclusion holds. In a molecule with a center of symmetry, vibrations that retain the center of symmetry are IR inactive and may be Raman active. Such vibrations, as shown in Fig. 2.12, generate a change in the polarizability during the vibration but no change in a dipole moment. Conversely, vibrations that do not retain the center of symmetry are Raman inactive, but may be IR active since a change in the dipole moment may occur. For molecules without a center of symmetry, some vibrations can be active in both the IR and Raman spectra. Molecules that do not have a center of symmetry may have other suitable symmetry elements so that some vibrations will be active only in Raman or only in the IR. Good examples of this are the in-phase stretches of inorganic nitrate and sulfate shown in Fig. 2.13. These are Raman active and IR inactive. Here, neither molecule has a center of symmetry but the negative oxygen atoms move radially simultaneously resulting in no dipole moment change. 20 2. BASIC PRINCIPLES

Raman active, IR inactive symmetric vibrations (a) (b)

O O O N O S O O O

Nitrate, in-phase Sulfate, in-phase NO3 stretch SO4 stretch (c)

X X

1,3,5-trisubstituted benzene, 2,4,6 C-radial in-phase stretch

FIGURE 2.13 Three different molecules, nitrate, sulfate, and 1,3,5-trisubstituted benzene molecules that do not have a center of symmetry. The in-phase stretching vibrations of all three result in Raman active, but IR inactive vibrations.

Another example is the 1,3,5-trisubstituted benzene where the C-Radial in-phase stretch is Raman active and IR inactive. In Figure 2.14 some additional symmetry operations are shown, other than that for a center of symmetry for an XY2 molecule such as water. These include those for a plane of symmetry, a two-fold rotational axis of symmetry, and an identity operation (needed for group theory) which makes no change. If a molecule is symmetrical with respect to a given symmetry element, the symmetry operation will not make any discernible change from the original configuration. As shown in Fig. 2.14, such symmetry operations are equivalent to renumber- ing the symmetrically related hydrogen (Y) atoms. Figure 2.15 shows the Cartesian displacement vectors (arrows) of the vibrational modes Q1,Q2, and Q3 of the bent triatomic XY2 molecule (such as water), and shows how they are C s s / modified by the symmetry operations 2, v, and v. For non-degenerate modes of vibration such as these, the displacement vectors in the first column (the identity column, I) are multiplied by either (þ1) or (1) as shown to give the forms in the other three columns. Multiplication by (þ1) does not change the original form so the resulting form is said to be symmetrical with respect to that symmetry operation. Multiplication by (1) reverses all the vectors of the original form and the resulting form is said to be anti-symmetrical with respect to that symmetry element. As seen in Fig. 2.15,Q1 and Q2 are both totally SYMMETRY: IR AND RAMAN ACTIVE VIBRATIONS 21

(a) Before After (b)

1 1 1 1 2 3 2 3 2 3 3 2 o Identity operation, I (no change) Two-fold axis of rotation, C2 (rotate 180 on axis) (c) (d)

1 1 1

2 3 3 2 2 3 2 3

Plane of symmetry, V (reflection in mirror plane) / Plane of symmetry, V (reflection in molecular plane)

FIGURE 2.14 Symmetry operations for an XY2 bent molecule such as water in the equilibrium conﬁguration.

I C 2 σV / σ V

(1) (1) (1) (1)

(1) (–1) (1) (–1)

FIGURE 2.15 The bent symmetrical XY2 molecule such as H2O performing the three fundamental modes Q1, I C s s / , Q2, and Q3. The vectors in column one (identity ) are transformed by the 2, v, and v operations into the forms in the remaining columns, where the vectors are like those in column one multiplied by (þ1) symmetrical or (1) anti- symmetrical. symmetric modes (i.e., symmetric to all symmetry operations), whereas Q3 is symmetric s / C s with respect to the v operation but anti-symmetric with respect to the 2 and v operations. The transformation numbers (þ1 and 1) are used in group theory to characterize the symmetries of non-degenerate vibrational modes. From these symmetries one can deduce that Q1,Q2, and Q3 are all active in both the IR and Raman spectra. In addition, 22 2. BASIC PRINCIPLES the dipole moment change in Q1 and Q2 is parallel to the C2 axis and in Q3 it is perpendic- s ular to the C2 axis and the v, plane. Doubly degenerate modes occur when two different vibrational modes have the same vibrational frequency as a consequence of symmetry. A simple example is the CeH bending e e vibration in Cl3C H molecule where the C H bond can bend with equal frequency in two mutually perpendicular directions. The treatment of degenerate vibrations is more complex and will not be discussed here.

9. CALCULATING THE VIBRATIONAL SPECTRA OF MOLECULES

The basis of much of the current understanding of molecular vibrations and the localized group vibrations that give rise to useful group frequencies observed in the IR and Raman spectra of molecules is based upon extensive historical work calculating vibrational spectra. Historically, normal coordinate analysis first developed by Wilson with a GF matrix method and using empirical molecular force fields has played a vital role in making precise assignments of observed bands. The normal coordinate computation involves calculation of the vibrational frequencies (i.e., eigenvalues) as well as the atomic displacements for each normal mode of vibration. The calculation itself uses structural parameters such as the atomic masses and empirically derived force fields. However, significant limitations exist when using empirical force fields. The tremendous improvements in computational power along with multiple software platforms with graphical user interfaces enables a much greater potential use of ab initio quantum mechanical calculational methods for vibrational analysis. The standard method for calculating the fundamental vibrational frequencies and the normal vibrational coordinates is the Wilson GF matrix method.8 The basic principles of normal coordinate analysis have been covered in detail in classic books on vibrational spectroscopy.1,4,5,8 In the GF matrix approach a matrix, G, which is related to the molecular vibrational kinetic energy is calculated from information about the molecular geometry and atomic masses. Based upon a complete set of force constants a matrix, F, is constructed which is related to the molecular vibrational potential energy. A basis set is selected that is capable of describing all possible internal atomic displacements for the calculation of the G and F matrices. Typically, the molecules will be constructed in Cartesian coordinate space and then transformed to an internal coordinate basis set which consists of changes in bond distances and bond angles. The product matrix GF can then be calculated. The fundamental frequencies and normal coordinates are obtained through the diagonal- ization of the GF matrix. Here, a transformation matrix L is sought: L 1 GFL ¼ L L l Here, is a diagonal matrix whose diagonal elements are i’s defined as: l ¼ p2c2 v2 i 4 i 1 2 Where the frequency in cm of the ith normal mode is ni . For the previous equation, it is the matrix L 1 which transforms the internal coordinates, R, into the normal coordinates, Q,as: Q ¼ L 1R CALCULATING THE VIBRATIONAL SPECTRA OF MOLECULES 23

In this equation, the column matrix of internal coordinates is R and Q is a column matrix that contains normal coordinates as a linear combination of internal coordinates. In the case of vibrational spectroscopy, the polyatomic molecule is considered to oscillate with a small amplitude about the equilibrium position and the potential energy expression is expanded in a Taylor series and takes the form: ! ! X3N vV 1 X3N X3N v2V V ¼ V0 þ dqi þ dqidqj þ ,,, vq 2 vq vq i ¼ 1 i e i ¼ 1 j ¼ 1 i j e q expressed in internal coordinates, i,, which are directly connected to the internal bond lengths and angles. The above expression is simplified: V ¼ 1. The first term o 0 since the vibrational energy is chosen as vibrating atoms about the equilibrium position. 2. At the minimum energy configuration the first derivative is zero by definition. 3. Since the harmonic approximation is used all terms in the Taylor expansion greater than two can be neglected. This leaves only the second order term in the potential energy expression for V. Using Newton’s second law, the above is expressed as: ! d2q vV X3N v2V i ¼ ¼ q dt2 vq vq vq j i i j j ¼ 1 e The above equation of motion is solved to yield a determinant whose eigenvalues (mu2) provides the vibrational frequencies (u). The eigenvectors describe the atomic displacements for each of the vibrational modes characterized by the eigenvalues. These are the normal modes of vibration and the corresponding fundamental frequencies. f The force constant ij is defined as the second derivative of the potential energy with q q respect to the coordinates i and j in the equilibrium configuration as: ! v2V f ¼ ij vq vq i j In order to obtain the molecular force field with the force constants given by the above equation, a variety of computational methods are available. In general, the calculations of the vibrational frequencies can be accomplished with either empirical force field method or quantum mechanical methods.9,10 The quantum mechanical method is the most rigorous approach and is typically used for smaller to moderately sized molecules since it is computationally intensive. Since we are examining chemical systems with more than one electron, approximate methods known as ab initio methods utilizing a harmonic oscillator approximation are employed. Because actual molecular vibrations include both harmonic and anharmonic components, a difference is expected between the experimental and calculated vibrational frequencies. Other factors that contribute to the differences between the calculated and experimental frequencies include neglecting electron correlation and the limited size of the basis set. In order to obtain a better match with the experimental frequencies, scaling factors are typically introduced. 24 2. BASIC PRINCIPLES

Quantum mechanical ab initio methods and hybrid methods are based upon force constants calculated by Hartree-Fock (HF) and density functional based methods. In general, these methods involve molecular orbital calculations of isolated molecules in a vacuum, such that environmental interactions typically encountered in the liquid and solid state are not taken into account. A full vibrational analysis of small to moderately sized molecules typically takes into account both the vibrational frequencies and intensities to insure reliable assignments of experimentally observed vibrational bands. The ab initio Hartree-Fock (HF) method is an older quantum mechanical based approach.9,10 The HF methodology neglects the mutual interaction (correlation) between electrons which affects the accuracy of the frequency calculations. In general, when using HF calculations with a moderate basis set there will be a difference of ca. 10e15% between the experimental and calculated frequencies and thus a scaling factor of 0.85e0.90. This issue can be resolved somewhat by use of post-HF methods such as configuration interaction (CI), multi-configuration self-consistent field (MCSF), and Møller Plessant perturbation (MP2) methods. Utilizing configuration interaction with a large basis set leads to a scaling factor between 0.92 and 0.96. However, use of these post-HF methods comes with a considerable computational cost that limits the size of the molecule since they scale with the number of electrons to the power of 5e7. The ab initio density functional theory (DFT) based methods have arisen as highly effective computational techniques because they are computationally as efficient as the original HF calculations while taking into account a significant amount of the electron correlation.9,10 The DFT has available a variety of gradient-corrected exchange functions to calculate the density functional force constants. Popular functions include the BLYP and B3LYP. The scaling factors encountered using a large basis set and BLYP or B3LYP often approach 1 (0.96e1.05). Basis set selection is important in minimizing the energy state of the molecule and providing an accurate frequency calculation. Basis sets are Gaussian mathematical functions representative of the atomic orbitals which are linearly combined to describe the molecular orbitals. The simplest basis set is the STO-3G in which the Slater-type orbital (STO) is expanded with three Gaussian-type orbitals (GTO). The more complex split-valence basis sets, 3-21G and 6-31G are more typically used. Here, the 6-31G consists of a core of six GTO’s that are not split and the valence orbitals are split into one basis function constructed from three GTO’s and another that is a single GTO. Because the electron density of a nucleus can be polarized (by other nucleus), a polarization function can also be included. Such functions include the 6-31G* and the 6-31G**. Accurate vibrational analysis requires optimizing the molecular structure and wave- functions in order to obtain the minimum energy state of the molecule. In practice, this requires selection of a suitable basis set method for the electron correlation. The selection of the basis set and the HF or DFT parameters is important in acquiring acceptable calculated vibrational data necessary to assign experimental IR and Raman spectra. CALCULATING THE VIBRATIONAL SPECTRA OF MOLECULES 25 References

1. Barrow, G. M. Introduction to Molecular Spectroscopy; McGraw-Hill: New York, NY, 1962. 2. Pauling, L.; Wilson, E. B. Introduction to Quantum Mechanics with Applications to Chemistry; McGraw-Hill: New York, NY, 1935. 3. Kauzmann, W. Quantum Chemistry, An Introduction; Academic: New York, NY, 1957. 4. Diem, M. Introduction to Modern Vibrational Spectroscopy; John Wiley: New York, NY, 1993. 5. Herzberg, G. Infrared and Raman Spectra of Polyatomic Molecules; D. Van Nostrand Company: New York, NY, 1945. 6. Long, D. A. Raman Spectroscopy; McGraw-Hill: New York, NY, 1977. 7. Cotton, F. A. Chemical Applications of Group Theory; Wiley (Interscience): New York, NY, 1963. 8. Wilson, E. B.; Decius, J. C.; Cross, P. C. Molecular Vibrations: The Theory of Infrared and Raman Vibrational Spectra; McGraw-Hill: New York, NY, 1955. 9. Handbook of vibrational spectroscopy, vol. 3, Sample Characterization and Spectral Data Processing; Chalmers, J. M., Grifﬁths, P. R., Eds.; John Wiley: 2002. 10. Meier, R. J. Vib. Spectrosc. 2007, 43,26e37.

CHAPTER 3

Instrumentation and Sampling Methods

1. INSTRUMENTATION

Raman scattering and IR absorption are signiﬁcantly different techniques and require very different instrumentation to measure their spectra. In IR spectroscopy, the image of the IR source through a sample is projected onto a detector whereas in Raman spectroscopy, it is the focused laser beam in the sample that is imaged. In both cases, the emitted light is collected and focused onto a wavelength-sorting device. The monochromators used in dispersive instruments and the interferometers used in Fourier transform instruments are the two basic devices. Historically, IR and Raman spectra were measured with a dispersive instrument. Today, almost all commercially available mid-IR instrumentation are (Fourier Transform) FT-IR spectrometers, which are based upon an interferometer (see below). Raman instruments include both grating-based instruments using multi-channel detectors and interferometer-based spectrometers.

1.1. Dispersive Systems

A monochromator consists of an entrance slit, followed by a mirror to insure the light is parallel, a diffraction grating, a focusing mirror, which directs the dispersed radiation to the exit slit, and onto a detector.1, 2 In a scanning type monochromator, a scanning mechanism passes the dispersed radiation over a slit that isolates the frequency range falling on the detector. This type of instrument has limited sensitivity since at any one time, most of the light does not reach the detector. Polychromatic radiation is sorted spatially into monochromatic components using a diffraction grating to bend the radiation by an angle that varies with wavelength. The diffraction grating contains many parallel lines (or grooves) on a reflective planar or on a concave support that are spaced a distance similar to the wavelength of light to be analyzed. Incident radiation approaching the adjacent grooves in-phase is reflected with a path length difference. The path length difference depends upon the groove spacing, the angle of incidence (a), and the angle of reflectance of the radiation (b).

27 28 3. INSTRUMENTATION AND SAMPLING METHODS

Incident radiation

1 2

Exiting radiation from adjacent grooves has path length difference

FIGURE 3.1 Schematic of a diffraction grating. Wavetrains from two adjacent grooves are displaced by the path length difference. Constructive interference can occur only when the path length difference is equal to the wavelength multiplied by an integer (ﬁrst, second, third order). The polychromatic radiation will be diffracted at different angles resulting in spatial wavelength discrimination.

Figure 3.1 shows a schematic of a diffraction grating with the incident polychromatic radiation and the resultant diffracted light. When the in-phase incident radiation is reﬂected from the grating, radiation of suitable wavelength is focused onto the exit slit. At the exit slit, the focused radiation will be in-phase for only a selected wavelength and its whole number multiples, which will constructively interfere and pass through the exit slit. Other wavelengths will destructively interfere and will not exit the monochromator. Thus, each of the grooves acts as an individual slit-like source of radiation, diffracting it in various directions. Typically, a selective ﬁlter is used to remove the higher-order wavelengths. When the grating is slightly rotated a slightly different wavelength will reach the detector.

1.2. Dispersive Raman Instrumentation

Raman instrumentation must be capable of eliminating the overwhelmingly strong Ray- leigh scattered radiation while analyzing the weak Raman scattered radiation. A Raman instrument typically consists of a laser excitation source (UV, visible, or near-IR), collection optics, a spectral analyzer (monochromator or interferometer), and a detector.1, 2, 3 The choice of the optics material and the detector type will depend upon the laser excitation wavelength employed. Instrumental design considers how to maximize the two often-conflicting parameters: optical throughput and spectral resolution. The collection optics and the monochromator must be carefully designed to collect as much of the Raman scattered light from the sample and transfer it into the monochromator or interferometer. Until recently, most Raman spectra were recorded using scanning instruments (typically double monochromators) with excitation in the visible region. An example of an array-based simple single grating-based Raman monochromator is depicted in Fig. 3.2. Use of highly sensitive array detectors and high throughput single monochromators with Rayleigh rejec- tion filters have dramatically improved the performance of dispersive Raman systems. The advent of highly efficient Rayleigh line filters to selectively reject the Rayleigh scattered radiation enables the instrument to use only one grating, thereby greatly improving INSTRUMENTATION 29

Slit Source M1 RF

M AD 2

FIGURE 3.2 Schematic of a simple array-based high throughput, single monochromator-based Raman instrument. For the source, laser light is scattered at 90 or 180 and collection optics direct light to a Rayleigh filter, RF, to remove G M M the Rayleigh scattered radiation. is the grating, 1 and 2 are spherical mirrors, and AD is the array detector. the optical throughput. Two commonly used filters include the “holographic notch” and dielectric band filters.3 Use of an array detector results in dramatically improved signal-to-noise ratio (SNR) as a result of the so-called multi-channel advantage. The array detectors (AD) are often photo- diode arrays or CCD’s (charge-coupled-devices), where each element (or pixel) records a different spectral band resulting in a multichannel advantage in the measured signal. However, only a limited number of detector elements (typically 256, 512, or 1064 pixels) are present in commercially available detector elements compared to the number of resolv- able spectral elements. Thus, to cover the entire spectral range (4000e400 cm 1) requires either low-resolution spectrum over the entire spectral range or high resolution over a limited spectral range. One solution to this is to scan the entire spectral range in sections using a multi-channel instrument and adding high resolution spectra together to give the full Raman spectrum.

1.3. Sample Arrangements for Raman Spectroscopy

Although the Raman scattered light occurs in all directions, the two most common experimental configurations for collecting Raman scattered radiation typically encountered are 90 and 180 backscattering geometry. Various collection systems have been used in Raman Spec- troscopy based upon both reflective and refractive optics. 1, 2, 3Figure 3.3 shows 90 and 180 collection geometries using refractive and reflective optics, respectively. The 180 collection optics are typically used in FT-Raman spectrometers and in Raman microscopes. The 180 collection geometry is the optimum sample arrangement for FT-Raman as a result of narrow band self-absorption in the near-IR region. Raman spectroscopy is well known to be a technique requiring a minimum of sample handling and preparation. Typical Raman accessories include cuvette and tube holders, solids holders, and clamps for irregular solid objects. Often NMR or capillary tubes are used and many times the Raman spectra can be measured directly on the sample in their container. 30 3. INSTRUMENTATION AND SAMPLING METHODS

(a)

To spectrometer

Laser (b) Laser

To spectrometer

FIGURE 3.3 Two different collection optics for Raman spectroscopy. In (a) a simple 90 collection geometry using refractive optics found in older dispersive instruments. In (b) 180 collection geometry using reﬂective optics typical of FT-Raman instrumentation.

1.4. Interferometric Spectrometers

Both FT-IR and FT-Raman spectroscopy use an interferometer to separate light into individual components.4, 5 The FT-Raman measurements use a Nd:YAG 1064 nm near-IR excitation laser and the Raman scattered light falls in the near-IR region. In the IR spectral region, significant improvements in instrumental performance are realized since the instrument measures all wavelengths of IR light simultaneously without use of an entrance slit. The simultaneous measurement of light results in a multiplex (or Felgett’s) advantage while the latter results in a throughput (or Jacquinot) advantage. The relative weakness of the source (both IR and the Raman scattered light) along with the poor detector sensitivity make the Fourier transform measurements attractive in this spectral region. Figure 3.4 shows the schematic of the Michelson interferometer. Use of an interferometer along with computation using the Fast Fourier Transform enables the generation of IR and Raman spectra from the time-dependent interferogram. The components in a Michelson interferometer include a beam splitter, and a fixed and moving mirror. The collimated light from the source incident on an ideal beamsplitter will be divided into two equal intensity beams where 50% is transmitted to the moving mirror and the other 50% is reflected to the fixed mirror. The light is then reflected off both mirrors back to the beamsplitter where 50% is sent to the detector and the other 50% is lost to the source. As the moving mirror scans a defined distance (Dl), the path difference between the two beams is varied and is called the optical retardation and is two times the distance traveled by the moving mirror (2Dl). The interferometer records interferograms caused by phase-dependent interference of light with varying optical retardation. The principle of operation can be easily described by first considering the source to contain only a single monochromatic wavelength, l. When the position of the moving mirror with INSTRUMENTATION 31

Fixed mirror

Lens

Source

Movable mirror

Beam splitter Lens

Detector

FIGURE 3.4 Schematic of a Michelson interferometer. The displacement of the moving mirror is indicated by Dl. respect to the beamsplitter is identical to that of the ﬁxed mirror, the optical retardation is zero (zero path difference) and the two beams will combine at the beamsplitter in-phase resulting in constructive interference for the beam passing through to the detector. The detector response will reach a maximum whenever the optical retardation is an integral number of the wavelengths (0, l,2l.). Similarly, a minimum detector response will result from destructive interference at optical retardation values with intervals of l/2 (l/2, 3l/ 2.). As the mirror scans at constant velocity, a simple sine wave will result as the two beams move in and out of phase. The Fourier transform of the sinusoidal interferogram will give rise to a single band with a characteristic frequency and intensity of the monochromatic source. If a polychromatic source is used, the interferogram will consist of a summation of all the different cosine functions corresponding to all of the wavelengths and of the intensities in the source. Only at zero path difference will all the wavelengths be in-phase. Thus, the resulting interferogram in FT-IR and FT-Raman spectra have a very strong center-burst and rapidly damped intensity in the wings of the interferogram. It is necessary to precisely know the optical path differences in the interferometer and this is accomplished using a heliumeneon laser. A computer is used to perform the fast Fourier transform to generate the spectrum, which can then be further processed. The computer interface in the FT-IR and FT-Raman spectrometers is used for setting measurement parameters, spectral processing, library searching, and for quantitation. 1.4.1. FT-IR SPECTROMETERS In a FT-IR spectrometer, sampling occurs just prior to the detector and its collimating optics. Various sampling techniques employed with IR spectroscopy are discussed below. 32 3. INSTRUMENTATION AND SAMPLING METHODS

Commercial FT-IR spectrometers typically operate in a single beam mode requiring sequen- tial measurements of the single beam background and sample spectra, which are then ratioed to provide the ﬁnal absorbance or %Transmittance IR spectrum. The single beam background spectrum provides a wavelength-dependent throughput of the instrument and is a function of the source emission, detector response, beamsplitter properties, and residual atmospheric absorptions from carbon dioxide and water vapor.

1.4.2. FT-RAMAN SPECTROMETERS Commercial FT-Raman spectrometers use mostly a 1064 nm Nd:YAG laser, notch filters at the laser wavelength to reduce Rayleigh scattered light entrance into the interferometer, high quality interferometers, and sensitive detectors which peak in the near-IR region. For FT-Raman spectrometers, the source depicted in Fig. 3.4 is the Raman scattered light. Presently, by switching only a few optical elements it is now possible to utilize one instrument to collect both the IR and Raman data. A major advantage of near-IR excitation based-FT-Raman spectroscopy is the greatly reduced fluorescence interference encountered for many compounds with visible excitation. This allows the Raman spectra of many compounds to be measured which was previously impossible. This occurs because the near-IR photons normally do not have sufficient energy to access the vibronic states that cause fluorescence. However, fluorescence problems are not completely eliminated for all samples and limitations due to sensitivity and absorption also exist. The y4 dependence shown by the Raman intensity is an intrinsic limitation to the sensitivity using near-IR excitation and can only be addressed by continued improvements in detector sensitivity. The inherent near-IR absorption profile of the sample itself can also pose significant problems. Many compounds have multiple absorption bands due to XeH type bonds in the near-IR spectral region which can attenuate the incident laser and/or the Raman lines. The unequal absorption throughout the Raman spectrum can affect the relative Raman band intensities and is termed as narrow band self-absorption. Thermal decomposition can sometimes occur due to absorption at the laser wavelength.

2. SAMPLING METHODS FOR IR SPECTROSCOPY

2.1. IR Transmitting Materials

Infrared spectroscopy can be used to study a wide range of sample types either in bulk or in microscopic amounts over a wide range of temperatures and physical states. Quite often, an IR transmitting material is needed to aid sampling. Since quartz strongly absorbs in the near-IR region, front-silvered or gold-coated reﬂective optics are often employed rather than refractive lenses. However, transmitting materials are needed for other materials including the beamsplitter. Table 3.1 summarizes some important infrared transmitting materials. For the majority of applications, NaCl or KBr windows are used and ZnSe is frequently used for aqueous or wet samples. The alkali metal halides fuse under pressure to give IR and optically transparent windows, but they are hygroscopic and fog if not treated properly. SAMPLING METHODS FOR IR SPECTROSCOPY 33

TABLE 3.1 Selected Infrared Transmitting Material

L Material Wavenumber range (cm 1) Refractive index Comments

NaCl 5000e625 1.52 Common, low cost, hygroscopic

KBr 5000e400 1.54 Common, low cost, very hygroscopic e BaF2 5000 870 1.45 Water insoluble, easily cracked e CaF2 5000 1100 1.40 Water insoluble, good at high pressures KRS-5 5000e275 2.38 Water insoluble, good ATR, deforms, poisonous ZnSe 5000e550 2.41 Water insoluble, good ATR Diamond 4500e2500, 1800e200 2.4 Very hard, inert, diamond Anvil cell also good for ATR

2.2. Sampling Techniques

The measured IR spectra are defined by the sample-preparation procedures and the optical spectroscopic techniques employed.6, 7 However, the quality of the spectra often depends upon the spectroscopist’s sample-preparation skills. A wide variety of sampling techniques exists; these are necessary to insure that the optimum spectrum will be measured for the varied physical sample states encountered by the analyst. For any given sample, there will usually be several different sampling techniques that can be used to obtain the spectrum. The available accessory equipment, personal preference of the analyst, or the nature of the particular sample will often dictate the selection of the technique. In general, the IR radiation incident upon a sample can be reflected, absorbed, transmitted, or scattered. Io ¼ Ir þ Ia þ It þ Is I I I I I Here o is the intensity of the incident radiation; r, a, t, and s are the intensities of the reflected, absorbed, transmitted, and scattered radiation, respectively. Experimentally, any of the above intensity components can be used to measure the IR spectrum of the sample. The extent that light is transmitted, reflected, scattered, or refracted is dependent upon the sample morphology, crystalline state, the angle of the incident light, and the difference in refractive indices of the sample and surrounding matrix. Figure 3.5 depicts the angular dependence of the transmission, refraction, and reflected light. Transmitted light has a 0 angle of incidence while reflectance (which includes specular, Q external, internal, and diffuse) is observed at larger angles. The critical angle ( c) beyond which refraction becomes imaginary and all light is reflected is also shown. In general, measurement of acceptable quality FT-IR spectra requires development of requisite sample-preparation skills necessary to measure photometrically accurate spectra. General criteria for suitable IR sample preparations include the following: 1. Suitable band intensities in the spectrum. The strongest band in the spectrum should have intensity in the range of 5e15% transmittance. The resulting preparation must be uniformly thick and homogenously mixed without holes or voids to insure a good quality spectrum. 34 3. INSTRUMENTATION AND SAMPLING METHODS

Transmitted

Refracted

n 2

n 1 c

Total Reflection

FIGURE 3.5 The angle of incidence of the light and the refractive index difference help deﬁne how much light is transmitted, refracted, and reﬂected.

2. Baseline. The baseline should be relatively flat. The highest point in the spectrum should lie between 95 and 100% transmittance. 3. Poor atmospheric compensation. Water vapor and carbon dioxide bands should be minimized. Since the sample scan is ratioed against a previously measured background spectral subtraction of water vapor/carbon dioxide, reference spectrum should be used. 4. X-axis scale. Plots should employ a 2X-axis expansion and not a simple linear X-axis. This provides an expansion of the important fingerprint region. Figure 3.6 shows the FT-IR spectrum of starch with two different sample preparations. In the top spectrum (A), the starch was dissolved in water and prepared as a cast film on ZnSe resulting in a good quality, photometrically accurate spectrum. In the case of starch, this is one of the preferred sample-preparation techniques. The Nujol mull preparation of powdered starch provides an unacceptably poor quality FT-IR spectrum and a so-called false spectrum. A broadening of the most intense bands and a strengthening of the weak bands characterize false IR spectra. In general, this is caused by a non-uniform sample film or distribution of sample in a Nujol of KBr matrix. In the case of starch, good quality IR spectrum cannot be obtained by either Nujol mulls or KBr discs. Starch demonstrates that the nature of the particular sample dictates what sample-preparation technique is appropriate.

2.3. Transmission IR

Simple transmission IR measurements are commonly made of gas, liquid, and solid-state samples. The most accurate information is obtained if the path length or analyte concentration is adjusted such that the peaks of interest have an absorbance between 0.3 and 0.9. The two simplest types of samples that can be prepared are gas phase samples and neat (low vola- tility) liquids. Gas phase measurements require only the introduction of the sample into a gas SAMPLING METHODS FOR IR SPECTROSCOPY 35

100

80 2152 1643 851 934 1240

60 1447 762 708 1410 1364 2928 40 %Transmittance

20 (A): Water cast film/ZnSe 1152 3380 1081

0 1026 100

80 2156 60

N 40 1643

%Transmittance N 20 850 1244 760 718

(B): Nujol mull 930 1153 3291 993 1373 1457 1081

0 2853 2922 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 Wavenumber (cm–1)

FIGURE 3.6 The FT-IR spectrum of starch prepared as (A) water cast film on a ZnSe plate and (B) Nujol Mull. The N marks the Nujol bands. cell, which can vary in path length from 10 cm to 8 meters. Highly accurate quantitation of single and multiple components is possible because the path length is well defined and no solid state effects are present (see below). 2.3.1. Liquids and Solutions Liquids and solutions are easily measured by FT-IR spectroscopy. Neat liquids can be easily prepared as a capillary film between two plates. The liquid film should be uniformly thick without holes or voids to insure a good, quantitative IR spectrum. Some common sample-preparation techniques for liquids include the following: 1. Capillary film. Neat liquids can be easily prepared as a capillary film. A drop of liquid sample is simply sandwiched between the cell windows. 2. Demountable cell. Here the technique is identical to the capillary film except a spacer (usually lead or teflon) is used to define the thickness of the liquid film. Disassembly allows access to the windows for easy cleaning or repolishing. The cell thickness is easily changed by selecting a different spacer. For a neat liquid sample, a thickness of about 0.01 mm is suitable. 36 3. INSTRUMENTATION AND SAMPLING METHODS

3. Sealed amalgam cell. This cell is constructed using a lead spacer which is amalgamated with mercury to create a very tight seal. This type of cell provides very accurate path length and is suitable for very volatile liquids. The ﬁlling and cleaning of the cell are done through the use of a pair of hypodermic syringe ﬁttings. Fixed path length cells are commercially available in path lengths from 15 mm to 500 mm and can be used to measure the analyte dissolved in a suitable solvent.

Both pure liquids and solutions can be measured using the above. Sealed amalgam cells are commonly used for solutions. Additional sample preparations include smears, cast ﬁlms, and analytes in solution. More viscous liquids can be prepared as a smear on a single window.

2.3.2. Cast Films Samples that have been dissolved in a volatile solvent can be prepared by casting a thin film and allowing the solvent to evaporate. The sample is dissolved into a moderate to highly volatile solvent, and a film is prepared by evaporating the solution directly onto an IR transmitting window. The non-volatile sample remains behind on the plate as a thin film. This sample-preparation technique is widely used, but not limited to, obtaining the IR spectra of polymers Typically, a uniform film can be obtained by spreading the film repeatedly on a window using a spatula or the edge of a capillary pipet. Ideally, the resulting film should be amorphous to eliminate scattering and crystallinity effects. In the case of smaller molecules, evaporation of the solvent can result in formation of a thin crystalline film. It is often important that identical solvents and drying conditions are employed for both the sample and the reference material. This can be important since in many cases, significant differences can be observed in the IR spectrum as a function of the crystalline form. When preparing a cast film, first select a suitable solvent and IR window. The solvent must not react with the sample, but should be volatile and dissolve the sample. For the majority of applications, NaCl or KBr windows are used and ZnSe is frequently used for aqueous solutions. Dissolve the sample in the selected solvent. The concentration is not critical, however, higher concentrations will result in faster sample preparation. Now add a few drops of the solution on the central portion of the infrared window. Gentle heating using a hot plate and a flow of nitrogen can be used to hasten the solvent evaporation. Care should be taken since some materials will decompose even under gentle heat. With more volatile solvents, the solution can be allowed to spread out over the surface of the window and as the solvent evaporates a thin film will remain. However, some solutions will not spread out evenly by themselves and will require manipulation to obtain a thin uniform film (see below). With less volatile solvents (for example water) or solutions that will not spread out evenly on the surface of the window, a flexible spatula or glass pipet should be used to spread a thin film and facilitate the solvent evaporation. For a uniform film, the solution may require a thin film to be stroked on. Examine the resultant film visually to confirm that a thin uniform film free of holes and voids has been prepared. The thickness of the film for FT-IR spectroscopy should be approximately 5 mm. There is only limited control over the thickness of a cast film. In general, the SAMPLING METHODS FOR IR SPECTROSCOPY 37 more concentrated the solution and the more drops placed on the window, the thicker the film. The process of obtaining the correct thickness is simply trial and error. Lastly, confirm from the IR spectrum that all of the solvent has evaporated leaving only the material of interest. The analyst should be familiar with the spectrum of the pure solvent.

2.3.3. SOLID-POWDERED SAMPLES: KBR DISCS AND NUJOL MULLS Solid-powdered samples can be prepared as fine particles dispersed in NUJOL or as a disk in a transparent KBr matrix. A NUJOL mull preparation simply mixes mineral oil and finely ground sample to form a paste, which is then sandwiched, between two IR transmitting windows. A KBr disc uses a mixture of dried KBr powder and finely ground sample. The KBr/sample mixture forms a clear disc when pressed under high pressure using a hydraulic press. Both preparations require that the sample must be sufficiently ground and mixed with the support matrix to insure a good, artifact free IR spectrum. Insufficiently mixed and ground sample particles result in undesirable spectral artifacts. Most obvious is a sloping baseline due to scattering. A distorted band shapes as a result of anomalous dispersion of the refractive index in an absorption band (Christiansen effect). False spectra due to non-uniform sample thickness are characterized by broadening of the bandshape of the strong bands and relative intensification of weak bands.

NUJOL MULL A Nujol mull involves mixing of mineral oil and finely ground sample to form a paste, which is then sandwiched, between two IR transmitting windows (typically KBr or NaCl). In general, 30e50 mg of sample is needed for this sample preparation. The sample must be ground to an average particle size of at least 0.5 mm using an agate mortar and pestle. Larger particles approaching the wavelength of light being used will scatter light resulting in a sloping background. A suitably ground sample will be evenly distributed over the mortar and takes on a smooth, glossy appearance. A very small amount of the mulling agent (mineral oil) is added to the mortar, and grinding is continued until the sample is suspended in the mulling agent to form a smooth, creamy paste. A small amount of the mull is transferred to the center of an infrared window. A second window is placed on top of the sample and the two are pressed together. The mull should be spread out into a thin translucent film, free of holes or voids. The representative IR spectra of Nujol and Fluorolube is shown in Fig. 3.7. Nujol has bands characteristic of a long chain hydrocarbon. If detailed information is needed in the CH stretching region and the deformation region, a Fluorolube (perfluorinated hydrocarbon) mull should be used which has no appreciable absorption bands from 4000 to 1350 cm 1. If necessary, a split-mull spectrum can be obtained by merging a Nujol and Fluorolube mull spectra. A significant advantages of Nujol mull sample preparation is that no water is introduced into the sample. This can be particularly important when trying to confirm the presence of an OH or NH type species or when analyzing a particularly hydroscopic material. When faced with analyzing particularly toxic solid materials, the analyst can limit potential exposure by simply mulling the sample between the salt plates. 38 3. INSTRUMENTATION AND SAMPLING METHODS

100 90 2297 723 80 438

70 1377 511 1463

60 650 1042

50 1273 598 40

30 902 %Transmittance 2955 2854 20 10 970 2925 1126 1199 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 Wavenumber (cm–1)

FIGURE 3.7 The FT-IR spectrum of Nujol and Fluorolube. The Nujol spectrum is shown as a solid line and the Fluorolube spectrum is shown as a dotted line.

KBR DISC SAMPLE PREPARATION A KBr disc involves mixing of dried KBr powder and ﬁnely ground sample. The KBr/ sample mixture forms a clear disc when pressed in a die under high pressure using a hydraulic press. Only 5 mg of sample is needed for this sample preparation. The sample must be ground to an average particle size of at least 0.5 mm using an agate mortar and pestle to minimize a scatter-induced sloping background. The sample concentration varies from 0.1% to 3% (by weight). In general, start with ca. 5 mg of sample and add 500 mg of KBr powder a little at a time and mix well. Transfer the thoroughly mixed KBr preparation into a 13 mm die. Press the disc in a bench top press. With a hydraulic press, anywhere from 2 to 8 tons is sufﬁcient. Solids are more frequently run as KBr discs than as mulls. This preference probably arises because KBr has no absorptions of its own over the entire transmission range and requires far less sample than a mull. However, the KBr disc method does have some disadvantages compared to a mull. KBr is very hygroscopic and some water is almost always introduced in the sample preparation. Figure 3.8 shows a KBr disc prepared without any organic sample. The water introduced from the sample grinding results in bands at ca. 3440, 1630, and 560 cm 1, from the OH stretch, OH bend, and OH wag that can complicate interpretation of the spectrum. KBr discs of crystalline materials are also sometimes less reproducible than mulls. The large pressure along with the addition of water can cause changes in hydra- tion state, crystallinity, or polymorphism. In some cases, the sample itself can ion exchange or react with KBr. 2.3.4. Melts Melts are the last commonly used IR sample technique that is particularly useful for polymers. This method involves melting the sample on a salt plate and allowing it to resolidify. This method is not recommended for crystalline materials because of possible orientation SAMPLING METHODS FOR IR SPECTROSCOPY 39

100 90

80 558 1632 70 60 3434 50 40 30 %Transmittance 20 10 0 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 Wavenumber (cm–1)

FIGURE 3.8 The FT-IR spectrum of a KBr disc prepared by mixing KBr powder using a mortar and pestle into a ﬁne powder and preparing a clear disc using a hydraulic press. Characteristic bands from water are observed at 3434, 1632, and ca. 560 cm 1. effects. If a sample is known to decompose under heat, this method should not be employed. The technique involves using a hot plate, heat the sample above its melting point, and allowing the sample to become a liquid. Next, using a pipet take one drop of the melt and place it on an IR transmitting window such as KBr. Use the pipet to draw down the liquid into a uniform ﬁlm and allow it to form a solid.

2.4. Reﬂection Techniques

Two of the more commonly used FT-IR sampling techniques that capitalize on the spectral information that can be obtained from reflection (and refraction) properties are ATR (attenuated total reflection or internal reflection) and DRIFTS (diffuse reflectance FT-IR spectroscopy). 2.4.1. Attenuated Total Reflectance (ATR) ATR is a contact sampling method that involves a crystal with a high refractive index and excellent IR transmitting properties. ATR is one of the more popular sampling techniques used by FT-IR Spectroscopists because it is quick, non-destructive and requires no sample preparation. It is a contact sampling method that involves an IRE (Internal Reflection Element) with a high refractive index and excellent IR transmitting properties. The sampling technique capitalizes on the spectral information that can be obtained from reflection phenomena. The technique is used to measure the IR spectra of surfaces or of material that is too thick or strongly absorbing to be analyzed by more traditional transmission methods. A variety of ATR accessory designs exist and are available from almost all manu- facturers of accessories for infrared spectrometry. In the case of ATR, the angle of incidence must be greater than the critical angle so that total internal reflectance occurs. Figure 3.5 depicted the dependence of light transmission, 40 3. INSTRUMENTATION AND SAMPLING METHODS refraction and reflection upon both the material refractive indices and the angle of incidence. However, the reflected light does contain spectral information about the sample at the sampleecrystal interface and the ATR technique capitalizes on this. A single reflection crystal is commonly used in micro-ATR work and a multiple reflectance ATR crystal is often used for bulk samples. An ATR accessory provides an IR spectrum of a sample because the radiation at the reflection point probes the sample with an “evanescent wave.” At a frequency within an absorption band, the reflection will be attenuated while at frequencies well away from an absorption band, all light is reflected. Internal reflectance occurs when the angle of incidence exceeds the “critical” angle. This angle is a function of the real parts of the refractive indices of both the sample and the ATR crystal h q ¼ sin1 2 C h1 h h Here, 2 is the refractive index of the sample and 1 is the refractive index of the crystal. Typical crystals such as Ge, ZnSe, or diamond have high refractive indices much higher than that of organics resulting in internal reflections at moderate angles of incidence. Figure 3.9 depicts some of the basic principals of ATR measurements. The refractive index of the sample is a complex with both a real and imaginary component: h ¼ n þ ik

The real part of this expression n in the regular refractive index holds when there is no absorption. The imaginary component of the refractive index, ik, holds within an absorption

Sample

e–z/dp

d O1 p

IRE O2

FIGURE 3.9 Diagram of a single reflection ATR crystal depicting the basic principles of the technique. SAMPLING METHODS FOR IR SPECTROSCOPY 41 band resulting in an effect known as anomalous dispersion. The parameter k is directly related to the extinction coefficient found in the LamberteBeer law. The total absorption intensity, A, as a function of q can be expressed as: Z N z= p AðqÞ¼ aðzÞe d dz 0 where z is the depth into the sample and a(z) is the absorption coefficient of the sample as a function of depth. As depicted in Fig. 3.9, the reflected radiation penetrates the sample boundary as a so-called evanescent wave. The electric field amplitude of this evanescent d wave exhibits an exponential dependence. The parameter, p, the effective penetration depth is expressed as: l d ¼ p 1=2 2pn sin2q n2 p sp l q n Where, equals the wavelength of the radiation, is the angle of incidence, p is the n ¼ n n refractive index of the IRE, and sp 2/ 1 the ratio of the refractive indices of the sample and IRE. This depth of penetration is defined as the distance from the IRE-sample boundary where the intensity of the evanescent wave decays to 1/e (37%)ofitsoriginal value. There are a number of important consequences to the above expression. The sampling depth of the ATR method is approximately 2e15 mm, is wavelength dependent, and increases with decreasing wavenumber. Experimentally, varying the angle of incidence of the light and the refractive index of the crystal used can control the sampling depth. Increasing either results in a decreased sampling depth. Careful comparison with classic transmission spectrum also indicates that ATR measurements result in small differences in the peak frequency and bandshape as a result of refractive index effects. ATR requires excellent contact between the sample and the crystal and is therefore an excellent method for liquids or soft, easily deformed solids. Use of micro ATR crystals with a protective ATR coating enable much greater pressure to be used to insure good contact between the ATR crystal and harder materials. Table 3.2 summarizes some of the commonly used ATR crystal materials.

2.4.2. Diffuse Reflectance Diffuse reflectance (DRIFTS, Diffuse Reflectance Infrared Fourier Transform Spectros- copy) is applied to analyze powders and rough surface solids. Typically, the technique is applied to powders since the technique relies upon scattering of radiation within the sample. The incident light on a sample may result in a single reflection from the surface (specular reflectance) or be multiply reflected giving rise to diffusely scattered light over a wide area which is used in DRIFTS measurements. Collection optics in the DRIFTS accessory are designed to reject the specularly reflected radiation and collect as much of the diffuse reflected light as feasible. In general, theories to describe the diffuse reflectance phenomena consider plane-parallel layers within the sample with light scattering in all directions. The observed reflectance 42 3. INSTRUMENTATION AND SAMPLING METHODS

TABLE 3.2 Commonly Used ATR)Crystal Materials and Characteristics

L Material Wavenumber range (cm 1) Refractive index Comments

Germanium 5000e850 4.0 Hard and brittle, good ATR material but temperature sensitive. KRS-5 5000e275 2.38 Water insoluble, conventional ATR material. Relatively soft, deforms, poisonous. Reacts with complexing agents. ZnSe 5000e550 2.41 Water insoluble, hard and brittle, good ATR material. Attacked by acids and strong alkalines.

Diamond 4500e2500 2.4 Very hard, inert, used in micro-ATR crystals. e Often used as a protective ﬁlm for ATR 1800 200 elements such as ZnSe Silicon 8300e1500 3.4 Limited wavelength range for ATR. Material is inert, hard and brittle.

* ATR is attenuated total reflectance. spectrum using the KubelkaeMunk equation is a ratio of the single beam spectra of the sample diluted by KBr powder against pure powder KBr and is defined as: 2 ð1 RNÞ K C fðRNÞ¼ ¼ ¼ 2RN s k where K is the absorption coefficient and s is the scattering coefficient of the sample material. The reflectance, RN, indicates the sample is thick enough that no radiation reaches the back surface. The above predicts a linear relationship between K and the maximum value of f(RN) for each peak provided s is constant. The scattering coefficient is dependent on the particle size and packing and must remain constant for reproducible results. Lastly, C is the concentration of the sample and k is related to the particle size and molar absorptivity of the sample, k ¼ s/2.303e. The DRIFTS spectrum can show a strong dependence on the refractive index of the sample, the particle size and size distribution, packing density, and sample homogeneity. For quantitative analysis, the particle size, sample packing, and dilution must be carefully controlled. To obtain the highest quality DRIFTS spectrum, the following precautions are taken. 1. Particle size should be small and uniform. This will result in narrower bandwidths and more accurate relative intensities. The sample/matrix particulates size should be 50 mmor less. 2. Dilute sample in a non-absorbing matrix powder such as KBr or KCl. The finely powdered sample is ~5% relative to the matrix powder. This insures a deeper penetration of the incident light into the sample, which will increase the diffuse scattered light. 3. Homogeneity. The samples should be well mixed. 4. Packing. The sample should be loosely packed in the cup to maximize the IR beam penetration. SAMPLING METHODS FOR IR SPECTROSCOPY 43

For quantitative analysis, the particle size, sample packing, and dilution must be carefully controlled. Despite compliance with the precautions listed above, the ratioed diffuse reﬂec- tance spectrum will appear different from that obtained with a classic transmission IR measurement. In general, low intensity bands will be increased relative to intense bands and the strong intensity bands will have broader, rounder peak shapes. A KubelkaeMunk conversion available in most FT-IR software packages can compensate for some of these effects.

2.5. Microscopy

Both IR and Raman spectroscopy have been very successfully coupled to microscopy with widespread applications in heterogeneous samples in industrial, forensic, and biological sciences. Vibrational microscopy is used for particle and contaminant analysis, studies of laminar structures, characterization of fibers, and domain structure and chemical composi- tional mapping. IR microspectroscopy involves coupling a microscope to an infrared (typically FT-IR) spectrometer and provides the capability to obtain spectra of extremely small samples (as small as 10 mm in diameter in certain specialized applications). The technique has widespread applications in the study of heterogeneous samples and is used for particle and contaminant analysis, studies of laminar structures, domain structures, and chemical compo- sition mapping. The microscope system allows one to focus IR radiation onto the sample, to collect and image transmitted or reflected IR radiation from the sample onto a sensitive detector and to view and position the sample. The system includes an optical microscope system for viewing the sample and reflective optics for imaging the IR radiation. The system also includes remote apertures for defining the spatial area of the sample to be examined. Commercial FT-IR microscopes are capable of a variety of sampling techniques including: specular reflectance, diffuse reflectance, micro-ATR, grazing angle, and conventional transmission measurements. Just as when studying materials in bulk, it is the sample itself that determines the most appropriate sampling technique. Several commercial Raman microspectrometers are available with excitation sources that span the UV to the near-IR. The ease of sampling makes Raman spectroscopy an excellent choice for microscopy. However, fluorescence remains a considerable obstacle to application of Raman microscopy to many samples. More recently, IR and Raman imaging have been successfully applied to a variety of heterogeneous systems. 2.5.1. Transmission IR Microscopy The ideal sample for transmission IR microscopy is a thin (5e10 mm), smooth, flat sample that does little to alter the optical path of the IR radiation. This requires the sample to also be large enough (ca. 25 mm) to minimize diffraction of light. Sample-preparation techniques can include: a) slicing and microtoming b) flattening sample with a roller c) squeezing sample between salt plates or a diamond compression cell As with macroscopic IR measurements, sample preparation plays an important role in obtaining quality IR spectra when using an IR microscope. Important experimental 44 3. INSTRUMENTATION AND SAMPLING METHODS parameters include the diffraction light limit, light scattering, and focal shifts due to high refractive index samples. When the sample or aperture size is on the order of the wavelength of light being used, diffraction plays a major role in the measured IR spectrum. Significant distortion of the measured IR spectrum occurs. Diffraction effects can be minimized by the: a) use of widest possible apertures. Keep aperture closed within the sample image but not closed enough to reduce energy throughput significantly. b) use of the same aperture setting in the background and sample scan. c) flattening of sample which will enlarge the sample area. Surface irregularities and fine particles can scatter light. Remedies include adding KBr or KI and applying pressure to obtain a clear plate or adding NUJOL oil to the a roughened surface. Samples or substrates with very high refractive index can give rise to focal shifts. This can be corrected by adjusting the focal system of the microscope by observing either the sharpness of the aperture edge or the energy throughput. At times unwanted internal reflections can also interfere. An example of this is interference fringes that can occur when using a diamond anvil cell. 2.5.2. Reflection IR Microscopy Infrared reflectance measurements are desirable because of the reduced sample preparation required. The IR microscope will be set to reflectance rather than transmittance mode and if necessary, to an additional attachment placed on the IR objective. Commonly used reflectance techniques include specular reflectance and ATR measurements. The most commonly used reflectance technique is ATR. A micro-ATR accessory is employed that attaches to the IR microscope objective. Once contact is established between the sample and the ATR element, the IR spectrum is measured. The resultant spectrum is typical of that obtained using any ATR accessory. Specular reflectance is a less commonly used technique for IR microscopy and involves a front surface mirror-like reflection from the exterior of a material where the angle of incidence is equal to the angle of reflection. The measured spectrum depends on the angle of incidence, the sample index of refraction, absorption properties, and sample surface morphology. The technique requires no sample preparation and is best suited for smooth, highly reflective surfaces and can include samples such as single crystals and thin films on a reflective metal surfaces. Not surprisingly, the resultant specular reflectance IR spectra are very different from typical transmission IR data. The spectra show derivative-like shape within the absorption bands. A KramerseKronig transformation which is often available in FT-IR software is often used to deconvolute the specular reflectance data and provide more absorbance- like spectra.

3. QUANTITATIVE ANALYSIS

Any quantitative analyses involve measurement of a test sample and comparison with standards of known concentration. The resulting calibration plot reﬂects the relationship QUANTITATIVE ANALYSIS 45 between the measured quantity (such as infrared absorbance or the Raman intensity) and the analyte concentration. Provided appropriate standards for calibration of an analytical method selected, vibrational spectroscopy is a valuable potential technique for quantitative analysis.1 Quantitative analysis methods can include both classical and chemometric PLS (principal least squares) analysis. Only classical analysis techniques will be discussed here. For an understanding of chemometric applications to spectroscopy the reader should consult a reference dedicated to this subject.8, 9 Advantages of using vibrational spectroscopy include the following: 1. Wide variety of sample types (gases, liquids, solids) 2. Clearly separated peaks are often found in the IR and Raman spectra 3. Unique bands frequently allow multicomponent analyses of mixtures 4. Typically not much effort is needed to acquire or prepare sample for analysis 5. Sample quantity is in milligram quantity Both the analyte and non-analyte components will be observed by both IR and Raman spectroscopy. Consequently, the main components of the sample must be conﬁrmed prior attempting quantitation. In general, Raman and IR spectroscopy of solids can be performed at concentrations of 1e100%. When strong isolated bands are available, this can be extended to lower concentrations (~0.1 %). IR spectroscopy can be employed to quantitate much lower concentrations (down to ppm levels) by greatly increasing the sample path length for solutions and for gases.

3.1. Relationship of IR and Raman Signal to Analyte Concentration

The basis of quantitative analyses in absorption spectroscopy is the LamberteBeer law. I 1 log 0 ¼ log ¼ A ¼ abC I T I I T where 0 is the incident light, is light after it has passed through the sample, is the transmittance, A is the absorbance, a is the absorption coefficient, b is the sample thickness, and C is the sample concentration. The absorption coefficient is a constant specific for the material at a particular wavelength. Where the LamberteBeer law holds, the measured absorbance is a linear function of the concentration (and path length). Both single component and multicomponent analysis is possible. Analytical methods based upon IR and Raman spectroscopy often use either peak heights or peak areas. Commercial instrument software presently allows both peak height and areas to be used when developing analytical methods. The integrated peak areas may provide a more robust calibration if the analyte band changes with increasing concentration or is influenced by molecular interactions. Deviations from the LamberteBeer law resulting in a non-linear relationship between the measured absorbance and the analyte concentration often occur. At the high concentrations typically encountered in IR measurements of solids, the molecular interactions of the sample itself will often cause non-linearity. However, if the calibration takes such non-linearity into account, it will not affect the quantitative accuracy of the analytical method. 46 3. INSTRUMENTATION AND SAMPLING METHODS

As discussed in the previous chapter, the intensity of the Raman scattered radiation is given by: va 2 I fn4I N R o vQ I N where o is the incident laser intensity, is the number of scattering molecules in a given state, n is the frequency of the exciting laser, a is the polarizability of the molecules, and Q is the vibrational amplitude, and the parameter ðva=vQÞis the Raman cross section. Analogous to infrared spectroscopy, the Raman cross section is a constant speciﬁc for the material at a partic- I ular wavelength. Thus, if the Raman cross section and the incident laser intensity ( 0) remain I constant, the intensity of the Raman band ( R) is directly proportional to the sample concentration. Once again, at the high concentrations often encountered in Raman measurements interactions of the components in the sample itself often result in non-linearity. To develop a quantitative analysis method for either IR or Raman spectroscopy, well-characterized standards covering a broad range of compositions are required. In the case of the IR spectra of solid-state samples, neither the sample thickness nor the concentration of the sample in the matrix is known. With Raman spectroscopy, the incident laser intensity can be very difﬁcult to precisely control. For this reason, a ratio of an analyte band is often normalized against another component to eliminate these sources of variation.6 The selection of appropriate peaks in the spectrum are chosen as the inputs for the quantitative analysis based on the spectral separation and knowledge of the underlying vibrational modes.

3.2. Quantitative Analysis: Ratio Method

A calibration curve deﬁnes the relationship between an analytical signal produced by the analyte and its concentration. In the common case of linear calibration, a linear regression will be used to ﬁt the analytical signal y to the concentration x of the analyte in calibration samples. y ¼ a þ bx

For determination of an unknown, the calibration equation is inverted. a y x ¼ þ b b A different form of calibration equation is often applicable in spectroscopy. The simplest C þ C ¼ case involves only two components ( 1 2 100%) with two isolated analytical bands with A A absorbances 1 and 2. Here, we assume a linear relationship between the concentration of the analytes and the observed signal with a slope that differs depending upon the analytes response function. For IR spectroscopy, this response will depend upon the molar absorptiv- ities of the bands and for the Raman cross section. This simple case is commonly used when employing the ratio method of IR analysis that relies upon Beer’s law and enables quantitation of components without knowledge of the sample path length. A b a 1 ¼ 1 1C1 ¼ k C1 A2 b2 a2C2 C2 QUANTITATIVE ANALYSIS 47

With simple rearrangement, we then obtain the following: 100 %C1 ¼ 1 þ kA2=A1 In general, the analysis is more complex since the calibration curves are often affected by overlapping bands, additional interfering components, molecular interactions effecting the absorption coefﬁcient and Raman cross sections and in the case of FT-Raman the self- absorption phenomena discussed below. Thus, the expressions for both IR and Raman are more complex than that suggested by the simple two component case. For IR, we could simply expand the original expression as: A1 ¼ a1b1C1 þ a2b2C2 For FT-Raman spectroscopy, the expression is more complex and below we add an addi- ax tional term (1e ) which takes into account near-IR self-absorption of the Raman scattered light. vs I NI 1 eaxÞþ Re o vU K

The resultant calibration curves will often be non-linear. Most instrumental software will enable the data to be fit with empirical equations such as quadratic or higher-order polyno- mial fits. An alternative is the use of a class of semi-empirical equations and linear fractional transformations. The equation form is suitable for the peak ratio method. Unlike quadratic equations, linear fractional transformations are easily inverted, which facilitates the development of calibration equations in a manner similar to the usual practice encountered in the linear calibration case. 3.2.1. Fractional Linear Calibration Equations Fractional linear transformation can be applied to account for typically encountered variation from the simple two-component case discussed above.10 For a mixture of two components A and B, a spectral response (absorbance or Raman intensity) in which there may be interference with the two analytical bands is R ¼ k C þ k C 1 1A A 1B B R ¼ k C þ k C 2 2A A 2B B C C þ C The ratio of concentrations A/( A B) (mole fraction) as a function of the ratio of the R R þ R spectral response 1/( 1 2) has the form of a fractional linear transformation C aR þ bR A ¼ 1 2 ðC þ C Þ R þ dR A B 1 2 where coefficients a, b, and d are constants which can be determined empirically. In our case, b will often equal zero and the above simplifies to an expression with only two variables: C aR A ¼ 1 ðC þ C Þ R þ dR A B 1 2 48 3. INSTRUMENTATION AND SAMPLING METHODS

The above equation can be employed for the non-linear calibration curves typically encountered in many IR and Raman quantitation procedures. C R 1 A ¼ 1 ¼ ðC þ C Þ R þ dR R2=R1 A B 1 2 1 þ d In a specialized case where a ¼ 1 and b ¼ 0, the above expression simpliﬁes to the standard expression for the ratio method of a linear system that we started with.

3.3. Example of Quantitation Using Ratio Method of Analysis

Below is an example of quantitation of the components in PAMeAETAC water-soluble copolymers using both FT-IR and FT-Raman spectroscopy. In this example, a broad selection of nine well-characterized PAMeAETAC standards are used to develop calibration curves for both IR and FT-Raman spectroscopy. Since the calibration curves are non-linear, a linear fractional transformation equation is used to model the non-linear calibration curves. The structure of poly AMDeAETAC is shown below.

poly (AMD—AETAC)

CH2 CH CH2 CH

C O C O

NH2 O m n CH2

CH2

N(CH3)3 Cl Copolymers of acrylamide (AMD) and 2-(acryloyloxy) ethyltrimethylammonium chloride (AETAC)

Figure 3.10 shows the FT-IR and FT-Raman spectra of pure PAM, and two PAMeAETAC copolymers with 53 and 90% AETAC(Q9) respectively. These spectra illustrate the many strong characteristic bands that exist for the polymer backbone, primary acrylamide, the ester carbonyl, and the positively charged trimethylammonium chloride groups. Table 3.3 lists assignments of some of the important IR and Raman bands for PAM and AETAC. Figure 3.11 shows the FT-IR and FT-Raman spectra of 47% AMD: 53% AETAC copolymers along with the selected baselines and peak heights used for this analysis. Bands characteristic of both groups are isolated and intense enough to provide quantitative bands for both components. In the IR spectrum, the quantitation method uses the AETAC ester carbonyl and the AMD amide carbonyl at 1734 and 1671 cm 1, respectively. In the FT-Raman spectrum, the quantitation method uses the AETAC trimethylammonium chloride band at 1 ca. 1 719 cm and the AMD primary amide NH2 rock band at 1105 cm . QUANTITATIVE ANALYSIS 49

Figure 3.12 shows the FT-IR calibration plot for AMDeAETEC copolymers using a peak height ratio and plotting the calculated ﬁt using nine calibration standards. The FT-IR calibration plot uses the peak height ratio of the AETAC ester carbonyl relative to the total carbonyl (ester þ amide). The non-linearity observed in the above IR calibration curve is a result of deviations in Beer’s law and overlapping contributions of the two carbonyl bands. The two variable functions chosen to model the calibration curve provides an excellent semi-empirical method to take into account these sources of non-linearity. The mole fraction AETAC with can be calculated from the FT-IR spectrum using the following expression: 1 1:088ðAbs:1734 cm Þ Mole fraction AETAC ¼ ðAbs: 1734 cm1Þþ0:874ðAbs:1670 cm1Þ

(a) 100

60 2858 783 2932 1124 1177 1323 40 1349 1419 20 1451 PAM 3199 3344 1621 1663 100

60 630 1055 2955 1340 3018

40 1414 %Transmittance 1629 954 1262 1450 1482 3169 20 3342 1166 PolyAMD—AETAC (52.5%) 1734 1671

100

60 877 1390 1057 2960 1671

40 1341 3013 1453 1256 955 3379

20 1485 PolyAMD—AETAC (89.6%) 1166 1733 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 Wavenumber (cm–1)

FIGURE 3.10 The FT-IR and FT-Raman spectra of the following: pure PAM and two PAMeAETAC copolymers (47/53 and 10/90). The FT-IR spectra are shown on the left and the FT-Raman spectra on the right. A cast ﬁlm sample preparation on ZnSe of all three samples after dissolving the powders in water was used for the FT-IR data. For the FT-Raman data, the samples were in the supplied crystalline form using an NMR tube for sampling. C NH NH CH C CH Group 3.3 TABLE NH CH 50 ¼ e N O 2 2 2 2 2 2 e e e CH CH CH %Transmittance (a) 100 100 100 20 40 60 80 20 40 60 80 20 40 60 80 oeBn sinet o h oyADATCSamples AMD-AETEC Poly the for Assignments Band Some 5030 5020 8010 4010 0080600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500

3379 3342 3344

3169 3199 .ISRMNAINADSMLN METHODS SAMPLING AND INSTRUMENTATION 3. 3013 3018 2932 1663 44(IR,R) 1424 A ad (cm Bands PAM 17(R) 1107 1608 (IR,R) 3200 3350, 45(RR 34(IR,R) 1324 (IR,R) 1455 (R) 2925 (IR) 2936 2960 2955 2858 e e 66(IR,R) 1656 61(IR,R) 1621 IUE3.10 FIGURE Wavenumber L 1 ) ( continued 1733 1734 1663 1671 1671 (

cm 1629 1621 –1 ).

) 1485 1482 1453 1450 1451 1390 1414 1419 1349 1341 1340 NH NH CH C novsC Involves Assignments NH CH(C CH 1323

¼ 1256 1262 str. O 2 2 2 2 2 bend str. ph. o. rock bend str. ph. o. and str. i.ph. 1166 1166 1177 ¼ )str. O) PolyAMD—AETAC (52.5%) PolyAMD—AETAC (89.6%) 1124 1057 1055 e

str. N 955 954 877 783

630 PAM QUANTITATIVE ANALYSIS 51

TABLE 3.3 Some Band Assignments for the Poly AMD-AETEC Samplesdcont’d

L Group PAM Bands (cm 1) Assignments ¼ e C O 1608 1621 (IR,R) NH2 bend AETEC

Ester C¼O 1734 (IR,R) C¼O str. Ester C¼O 1166 (IR) Involves CeO str. e e CH2 N(CH3)3 3010 3022 (IR,R) CH3 o. ph. str. e þ CH2 N(CH3)3 955 (IR,R) Involves NC4 o. ph. str. CH3 rock e CH2 N(CH3)3 720 (R) Involves NC4 i. ph. str. Ester C¼O 1734 (IR,R) C¼O str.

Peak Ht AETAC 0.9 C=O Poly AMD(47%) — AETAC(53%) 1671 0.8 1734 Peak Ht AMD C=O 0.7 0.6

0.5 1166 0.4 1482 1450 954

0.3 1262 Absorbance 1416 0.2 0.1 0.0

30 719 Peak Ht AETAC NC4 i.ph str.

25 1450

20 Peak Ht AMD NH2 rk 953 15 846 874 1340 10 1089 1107 1036 1242 Raman intensity 1732 5 1673 1620

1800 1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 600 Wavenumber (cm–1)

FIGURE 3.11 The baseline and peak height measurements used for quantitation. The top FT-IR spectrum shows the peak heights used to quantitate the ester and amide carbonyl bands. The bottom FT-Raman spectrum shows the peak heights used to quantitate the amide NH2 rock and the cationic ammonium NC4 in-phase stretch bands. 52 3. INSTRUMENTATION AND SAMPLING METHODS

1.0

A (1733 cm ) [A (1733 cm) + A (1670 cm )] 0.8 1.088 (A 1733 cm ) (A 1733 cm) + 0.874 (A 1670 cm )

0.6

0.4

C=O Absorbance ratio 0.2

0.0 0.0 0.2 0.4 0.6 0.8 1.0 Mole fraction AETAC

FIGURE 3.12 FT-IR calibration plot for AMDeAETAC copolymers. The form of the fractional linear transformation used to ﬁt this data is only very slightly non-linear.

1.0

0.8

0.6

I (719 cm ) 0.4 [I (719 cm) + I (1105 cm )] Raman intensity ratio 2.39 (IR719 cm ) 0.2 [(I 719 cm) +15.96 (I 1105 cm )]

0.0 0.0 0.2 0.4 0.6 0.8 1.0 Mole fraction AETAC

FIGURE 3.13 The FT-Raman calibration plot for powdered AMDeAETAC copolymers. The form of the fractional linear transformation used to ﬁt this data is quite non-linear.

Figure 3.13 shows the FT-Raman calibration plot for AMDeAETEC copolymers using a peak height ratio and plotting the calculated ﬁt for the same nine standards. The form of the fractional linear transformation used to ﬁt this data is quite non-linear. Despite this, the FT-Raman technique provides excellent quantitation of PAMeAETAC copolymers. The mole fraction AETAC with can be calculated from the FT-Raman spectrum using the following expression: QUANTITATIVE ANALYSIS 53

0.6

0.5 500 1000 2000 3000 4000

0.4

0.3

Absorbance 0.2

0.1

0 Poly AMD–AETAC (90%) PAM

1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 Wavelength (nm)

FIGURE 3.14 The diffuse reﬂectance near-IR spectra of pure PAM and poly AMDeAETAC (90%) copolymer. Note the different absorbances at 1152 and 1206 nm where the analytical Raman bands are located.

2:39ðI 719 1Þ ¼ R cm Mole fraction AETAC ½ðI 719 1Þþ15:96ðI 1105 1Þ R cm R cm The significant non-linearity in the calibration curve above is due largely to narrow band self-absorption phenomena that are typical of 1064 nm excitation-based Raman spectra.1 Such self-absorption is defined as the absorption of the Raman scattered light by the sample near-IR absorption bands themselves before the light can escape the sample in the NMR tube used in this experiment. Where there is a near-IR absorption band, the Raman band intensity will be decreased. The magnitude of this effect will vary significantly in powdered samples because of the variation in the path lengths the scattered light will follow. In a liquid sample, the magnitude of the Raman band suppression will follow a simple the LamberteBeer law. Figure 3.14 shows the diffuse reflectance near-IR spectra of pure PAM and poly AMDeAETAC (90%) copolymer. The 719 cm 1 AETAC band and the 1105 cm 1 PAM band both have different near-IR absorbances for these two components. Much of the observed curvature in the correlation plot is a consequence of this self- absorption process and not molecular environmental induced changes in the Raman cross sections. 54 3. INSTRUMENTATION AND SAMPLING METHODS

Chapter 3: Questions 1. Outline the dispersive unit used in an FT-IR spectrometer to separate light into individual components. 2. Summarize the four guidelines for quality FT-IR spectrum. 3. Good sample-preparation skills are necessary to acquire photometrically accurate, high quality IR spectra. How can one differentiate between a good and a false IR spectrum? What causes a false IR spectrum? 4. Describe general regions of the fundamental vibrational spectrum with some characteristic group frequencies. 5. Outline one type of dispersive unit used in a Raman spectrometer to separate light into individual components. 6. Describe components of a Raman Fiber optic Probe. 7. List advantages and disadvantages of Raman spectrometers. Consider wavelength selection. 8. What is the difference between Rayleigh and Raman scattered light? 9. Summarize the advantages and disadvantages to KBr disc and Nujol mull sample preparations. 10. Does Raman or IR spectroscopy differentiate between amorphous and different crystalline materials? 11. Illustrate how light can be transmitted, refracted, and reflected through a crystal. What are the important variables? 12. What samples will provide the best quality IR spectrum using an ATR accessory and why? The worst? 13. How does an ATR measured spectrum differ from a classically measured transmission spectrum? What important parameters can the experimenter control? 14. Define the evanescent wave described by ATR theory. How does it define the sampling depth? 15. Identify three important criteria for selecting suitable ATR crystals. 16. What are the ideal sample characteristics for transmission IR microscopy? 17. List unwanted optical effects encountered in IR microscopy. 18. What is the diffraction light limit and what limits does it impose on IR microscopy?

References

1. Infrared and Raman Spectroscopy, Methods and Applications; Schrader, B., Ed.; VCH: New York, NY, 1995. 2. Diem, M. Introduction to Modern Vibrational Spectroscopy; John Wiley: New York, NY, 1993. 3. Analytical Applications of Raman Spectroscopy; Pelletier, M. J., Ed.; Blackwell Science: London, 1999. 4. Grifﬁths, P. R.; de Haseth, J. A. Fourier Transform Infrared Spectroscopy; John Wiley: New York, NY, 1986. 5. Chase, D. B.; Rabolt, J. F. Fourier Transform Raman Spectroscopy, From Concept to Experiment; Academic: 1994. 6. Colthup, N. B.; Daly, L. H.; Wiberley, S. E. Introduction to Infrared and Raman Spectroscopy, 3rd ed.; Academic: New York, NY, 1990. 7. Coleman, P. B. In Practical Sampling Techniques for Infrared Analysis; CRC: Boca Raton, 1993. 8. Beebe, K. R.; Pell, R. J.; Seasholtz, M. B. Chemometrics A Practical Guide; John Wiley: New York, NY, 1998. 9. Martens, H.; Naes, T. Multivariate Calibration; John Wiley: New York, NY, 1989. 10. Peter Fortini, personal communication. CHAPTER 4

Environmental Dependence of Vibrational Spectra

1. SOLID, LIQUID, GASEOUS STATES

Vibrational spectroscopy shows a strong dependence on the environment of the molecule being examined. The IR and Raman spectra are significantly different for molecules in the gaseous, liquid, or solid state. In the gaseous state, the molecules can be considered to be non-interacting and can rotate freely with a characteristic angular momentum. (We are ignoring pressure broadening.) Coupling of the vibrational transition with the rotational degrees of freedom of the molecule occurs resulting in band structure that is highly characteristic of the molecular structure and rotationalevibrational interactions.1,2 This band structure is highly dependent upon the molecular symmetry and falls into four basic types: linear (e.g., diatomics, CO2) spherical top (e.g., CH4,SF6), symmetric top (oblate e.g. CHCl3 prolate e.g., CH3Cl), and asymmetric top (e.g., H2O). Numerous qualitative and quantitative gas phase applications exist using both IR and Raman techniques but will not be covered here. Rotational fine structure can be observed in the vibrationalerotational band cluster if the molecular moment of inertias are sufficiently low as it is typical for simpler molecules. Fine structure occurs because angular momentum is also quantized. For larger molecules, the fine structure is typically unresolved resulting in broad bands. However, the band contour reveals the molecule symmetry and the direction of the dipole moment change during the vibration. Figure 4.1 shows the classical description of the IR gas phase contours of carbon dioxide, a linear type rotator. In Fig. 4.1a,CO2 is bending and rotating about an axis parallel to the change in the dipole moment which is not affected by the rotation. As seen in Fig. 4.1b, this results in a single frequency depicted in Fig. 4.1c.InFig. 4.1d, this rotation changes the orientation of the dipole moment vector, the vertical component which shown in Fig. 4.1e interacts with the radiation oscillating in the vertical plane. This complex wave function can be resolved trigonometrically into two steady amplitude waves which give rise to two lines in the spectrum at V R and V þ R (see Fig. 4.1f). Although the molecule vibrates at only one frequency, the rotational frequency varies, giving rise to two broad wings on the central band shown without fine structure. The total band cluster is shown in Fig. 4.1g as the sum of Fig. 4.1c and Fig. 4.1f. As shown in Fig. 4.1h and Fig. 4.1j, the CO2 molecule is

55 56 4. ENVIRONMENTAL DEPENDENCE OF VIBRATIONAL SPECTRA

Change in Time (a) dipole moment (b) (c) Vibrational

(g) Total band Vertical component CO2bending and rotating of dipole moment V – R V + R

Dipole moment (f) change is (d) (e) perpendicular Vibration +– Rotation to the bond axis R is variable (h) Change in dipole moment (k) Total CO2 band Out-of-phase stretching and rotating

Dipole moment (j) change is parallel to the bond axis

FIGURE 4.1 Classical treatment describing the IR gas phase contours of CO2. Although the molecule vibrates at only one frequency, the rotational frequency varies, giving rise to two broad wings on the central band shown without ﬁne structure. In this case the CO2 molecule cannot rotate without rotating the dipole moment vector and the total band contour shown in (k) is a broad doublet with no central peak.

stretching out-of-phase. In this case, the CO2 molecule cannot rotate without rotating the dipole moment vector and the total band contour shown in Fig. 4.1k is a broad doublet with no central peak. Figure 4.2 shows the characteristic band clusters for three different vibrational modes of a para-substituted aromatic, an asymmetric top rotator. In larger molecules such as these, the rotational fine structure is typically not observed. The white arrows in the first two in- plane vibrations and a white plus sign for the last out-of-plane vibration indicate the dipole moment changes. These vectors are each parallel to one of the axes of rotational moments of inertia as shown in the figure. The rotational moments in the condensed phase state molecules can and do interact and these interactions strongly effect the vibrational spectrum. In the liquid state, molecules may have any orientation relative to the spectrometer. Further, a molecule may be found in several conformations, all of which may have different spectra (e.g., rotational isomers). No rotational fine structure is observed and the resulting overall spectrum may consist of a large number of fairly broad bands. Here, hydrogen bonding can have a dramatic effect on the IR and Raman spectra. Typically, if the molecule is associated, the bands will also be broader than for the non-associated state. HYDROGEN BONDING 57

O O O o o o o + o o + --+ B -- o o o o + o + o + O O O

~ 1013 cm–1 ~1117 cm–1 ~ 817 cm–1 (a) (b) (c)

FIGURE 4.2 Asymmetric top gas phase band contour (para-substituted benzenes). inertia are at a minimum at (a), intermediate at (b), and at a maximum for (c). In the bottom row are typical gas phase IR spectra showing the gas phase contour for a, b, and c+ type bands. The b type bands have no central peak. In a and c type bands, the relative intensities of the central peaks to the band wings vary with changes in the relative a, b, and c moments of inertia.

Lastly, in the solid state, the crystallinity (or lack of it) of the molecule can be quite important and the nature of the sample preparation techniques employed can also be important. Figure 4.3 shows the IR spectra of common table sugar (sucrose) prepared as a KBr disc and as a cast film from water and clearly illustrate the differences observed in the IR spectrum of a crystalline and amorphous material. The large number of sharp bands evident in the upper spectrum is characteristic of a crystalline solid. When sugar is prepared as a water cast film, it becomes an amorphous material resulting in broader less distinct bands seen in the lower spectrum. Both spectra have some water present. In general, crystalline solids can be frozen into one or more configurations fixed in a lattice resulting in sharper bands. Often, crystalline splitting of degenerate vibrations can occur and forbidden vibrations may result in weak bands. Vibrational spectroscopy can distinguish between different crystalline forms and quantitatively assay mixtures. This ability has been exploited for various applications.

2. HYDROGEN BONDING

Both IR and Raman spectroscopies are very sensitive to the molecular interactions involved in hydrogen bonding.3 The hydrogen bond itself involves an association of a hydrogen atom from an XeH group of a molecule with the Y atom of another group (XeHeY).4,5 The X type atoms involved often have high electronegativities resulting in an 58 4. ENVIRONMENTAL DEPENDENCE OF VIBRATIONAL SPECTRA

100 KBr disc, crystalline solid

80 2476 1628 2723 60 729 1279 %Transmittance 1461 683 2940

40 1239 1431 866 1347 583 552

20 910 3563 1124 991 1069 3388

100 Cast film, amorphous

80 2124 1648

60 864 833 1265 1336 1420 587 %Transmittance 40 2932 928

20 1134 996 3351 1053 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 Wavenumber (cm–1)

FIGURE 4.3 The FT-IR spectra of common table sugar. The upper spectrum was prepared as a KBr disc while the lower spectrum was prepared as a water cast ﬁlm on ZnSe.

XeH bond which is partially ionic while the HeY bond is suggested to be mostly electrostatic with some weak covalent characteristics. In general, hydrogen bonding to an XeH group results in a decrease in the XeH stretching frequency accompanied by a broadening and intensiﬁcation of this band. Both OH and NH groups are found to show highly characteristic changes with hydrogen bonding. Figure 4.4 shows the OH stretches for two different phenolic OH stretches. The steric hindrance provided in 2,6-di-tert-butylphenol results in a strong sharp band at 3645 cm 1 characteristic of a non-hydrogen bonded OH group. Conversely, the easily accessible OH group of p-creosol results in a broad strong band at 3330 cm 1 characteristic of intermolecular hydrogen bonding between different phenolic OH groups. Intermolecular hydrogen bonding in chemical systems are very common. Exam- ples of the condensed phase hydrogen bonded OH and NH stretching frequencies for carboxylic acid dimer and isocyanuric acid are shown below. Carboxylic Acid Dimer O OH R C C R OH Str. ~ 3000 cm–1 OH O HYDROGEN BONDING 59

100

80 OHOH R R OH 3083 60 (CH ) C C(CH )

3 3 3 3 3024

40 OH %Transmittance

20 3330 3645 CH “Free” OH Hydrogen-bonded OH 3

4000 3800 3600 3400 3200 Wavenumber (cm–1)

FIGURE 4.4 The solid state IR spectrum of para-creosol and 2,6-di-tert-butylphenol illustrating the effect of hydrogen bonding on the OH stretching frequency.

Isocyanuric acid: Note that all of the NH and C¼O groups are involved in hydrogen bonding but only one set is shown for simplicity.

O H H C H O N O N N C C NH Str. ~ 3209, 3080 cm–1 C C N N O N O H C H H O

The carbonyl C¼O stretching frequency for the carboxylic acid dimer and the isocyanuric acid molecules also have a lower frequency and broader bandwidth as a result of hydrogen bonding. Additional changes in the vibrational spectrum of molecules involved in hydrogen bonding also occur. Bands involving XeH bending will usually increase in wavenumber upon formation of the hydrogen bond. The resultant changes in frequency and bandwidth are not as pronounced as observed in the XeH stretching region. Lastly, new low frequency bands can often be seen involving the stretching and bending of the HeY bond. The OHeO out-of plane hydrogen bend of the carboxylic acid dimer (960e875 cm 1) is a classic well- known example of this. Intramolecular hydrogen bonding can have a dramatic effect on the IR and Raman spectra and typically favors formation of ﬁve- and six-membered rings. Conjugated intramolecular hydrogen bonding systems in particular can result in very strong hydrogen bonds. Examples of this include the keto-enol conjugated system which involves conjugated ketone and hydroxy groups. As shown below, a resonance structure can be drawn that places the 60 4. ENVIRONMENTAL DEPENDENCE OF VIBRATIONAL SPECTRA negative charge on the carbonyl oxygen and a positive charge on the oxygen carrying the hydrogen bonding proton.

H H O O O O

C C C C CH CH Some examples of intramolecularly hydrogen bonded systems are shown below.

2-Hydroxy-4-(methoxy)-benzophenone H O O C OH Str. ~2900 cm–1

OC H3

2-(4,6eDiphenyle1,3,5etriazinee2eyl)e5 alkyloxy phenol

NN H OH Str. ~ 2900 cm–1 O

3. FERMI RESONANCE

The vibrational spectrum of a molecule typically is considered to have isolated vibrational coordinates resulting fundamental vibrations. For example, carbon dioxide which has four total vibrations (3n 5) has two IR active vibrations, an out-of-phase stretch and a doubly degenerate deformation and a Raman active in-phase stretch. However, under certain conditions the vibrational levels are not well separated and can interact leading to phenomena such as Fermi resonance.6 Such interaction requires suitable symmetry for the two vibrations, an anharmonic nature of the vibration, and a similar energy for the two states (typically within 30 cm 1). The vibrations cannot be signiﬁcantly separated within distinctly different parts of the molecule and they must mechanically interact in order for the two vibrations to mix. In most cases, Fermi resonance involves a fundamental that interacts with a combination or overtone band resulting in two relatively strong bands where only one nearly coincident fundamental is expected. Figure 4.5 shows the idealized vibrational spectrum for a stretching and bending vibration before (Fig. 4.5a) and after Fermi resonance along with the idealized energy level diagram. The idealized Fermi resonance shown involves the overtone of FERMI RESONANCE 61

1.8 + 2 δ + x 1.6 s –

1.4 s 1.2 (b) 1.0 2 δ 0.8 Intensity s 0.6 0.4 s 0.2 δ (a) 0.0

3500 3000 2500 2000 1500 1000 Wavenumber (cm–1)

FIGURE 4.5 Schematic diagram illustrating Fermi resonance. The idealized vibrational spectrum for a stretching and bending vibration are shown before (a) and after Fermi resonance (b). To the left of the idealized spectra is the energy level diagram.

n n a bending vibration ( d) with a symmetric stretching vibration ( S) that results in a classic Fermi resonance doublet that straddles the original symmetric band frequency. The Raman spectrum of carbon dioxide shown in Fig. 4.6 provides a classic example of Fermi resonance.6 1 Only one band for the CO2 in-phase stretch fundamental is expected (1332 cm ) but a classic Fermi resonance doublet is observed at 1385 and 1278 cm 1 instead. The two Raman bands are a linear combination of the fundamental in-phase stretch and the CO2 bend overtone.

100 80 CO 60 3600 2 3728 gas phase CO2 bend 40 Combination band: CO2 i.ph. str. + CO2 o. ph. str. 669

%Transmittance 20 2360 2324 0.20 Fermi resonance doublet: CO2 o. ph. str. 1385 CO2 i. ph. str. + CO2 bend overtone 0.15 2 Χ 669 = 1338 0.10 1278 1385 + 1278 = 1331 0.05 2 Raman intensity 0.00 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 Wavenumbers (cm–1)

FIGURE 4.6 The IR and Raman spectra of carbon dioxide. Note the Fermi resonance doublet at 1385 and 1 y ¼ y ¼ 1 1278 cm resulting from interaction of the 1CO2 i.ph. str. and the 2 (overtone) of the 669 cm CO2 bend. 62 4. ENVIRONMENTAL DEPENDENCE OF VIBRATIONAL SPECTRA

TABLE 4.1 Selected Groups that Display Fermi Resonance Bands in their Vibrational Spectrum.

Active Group Bands (cmL1) Assignment IR Raman

þ CO2 1385, 1278 CO2 i. ph. str 2x CO2 bend No Yes ReC(¼0)eH ~2820, ~2710 CH str. þ 2x CH i.ph. bend Yes Yes N¼C¼O ~1300, ~1200 NCO i.ph. str. þ 2x NCO bend Yes Yes ReCOOH ~3000e2650 OH str. þ 2x OH i. pl bend Yes Yes ~3000e2550 OH str. þ 2x C-O str. Yes Yes e þ CH2 ~2920 2890 CH2 str. 2xCH2 bend Yes Yes AryleC(¼O)eCl ~1780, ~1730 C¼O str. þ 2x 880 aryl-C str. Yes Yes h e ¼ h þ þ 1 e N C N C(NH2)2 2200, 2170 C N str. (1250 925 cm ) Yes Combination band ReChCeR 2300, 2235 ChC str þ CeChC bend No Yes C¼O 1810, 1780 C¼O str. þ 2x ~900 ring bend Yes e e þ Aryl NH2 3355, 3205 NH2 i. ph. str. 2x NH2 bend Yes Yes þ NH4Cl 2825 NH4 i. ph. str. 2x NH4 bend Yes Yes e C(¼O)eNHeC 3300 (s), 3100(m) MH str. þ 2x CNH str.-bend Yes Yes

Also noteworthy is that the combination band deriving from the bands involving the CO2 in- phase str. and o. ph. str. are observed as two doublets in the 3728e3600 cm 1 region because of the Raman active CO2 in-phase str. Fermi resonance doublet. In general, Fermi resonance has several effects on the vibrational spectrum. As illustrated by the carbon dioxide case, the resultant bands are shifted from their expected frequency. Furthermore, the intensity is greater than expected for a simple overtone band. Lastly, because the frequencies of the fundamentals themselves are typically environmentally sensitive, changes in solvents or crystalline state can affect the observed Fermi resonance band intensities. Fermi resonance can be found in the IR and Raman spectra of a signiﬁcant amount of functional groups.3 Table 4.1 summarizes some groups that display Fermi resonance in the vibrational spectrum, with their band frequencies, assignments, and activities.

References

1. Barrow, G. M. Introduction to Molecular Spectroscopy; McGraw-Hill: New York, NY, 1962. 2. Infrared and Raman Spectroscopy, Methods and Applications; Schrader, B., Ed.; VCH: New York, NY, 1995. 3. Colthup, N. B.; Daly, L. H.; Wiberley, S. E. Introduction to Infrared and Raman Spectroscopy, 3rd ed.; Academic: New York, NY, 1990. 4. Pimentel, G. C.; McClellan, A. L. The Hydrogen Bond; Freeman: San Francisco, California, 1960. 5. Bene, J. E.; Jordan, M. J. T. Int. Rev. Phys. Chem. 1990, 18 (1), 119e162. 6. Diem, M. Introduction to Modern Vibrational Spectroscopy; John Wiley: New York, NY, 1993. CHAPTER 5

Origin of Group Frequencies

When a molecule contains a bond or group with a vibrational frequency signiﬁcantly different from adjacent groups, then the vibrations are localized primarily at this group. Such characteristic IR and Raman bands for particular bond or group are called “group frequencies” and are extremely useful for both qualitative and quantitative analysis. In order to understand the origin of these group frequencies, coupled oscillator systems are presented here and related to actual chemical groups. These model systems are based upon a classical description of different general types of mechanical coupling of bond vibrations.1,2,3 This overview enables us to provide a framework to understand the sensitivity of vibrational spectra to molecular structure. Lastly, some general rules concerning mechanical coupling of vibrations are presented.

1. COUPLED OSCILLATORS

The simplest coupled oscillator system to consider is the stretchestretch interaction of a linear triatomic molecule.1,2 Here, only two bonds with two stretching vibrations are present which will mechanically couple. The two-coupled oscillators exert forces on each other when they oscillate, resulting in both in-phase and out-of-phase stretching vibrations (see Fig. 5.1). The out-of-phase stretch is of higher frequency than the in-phase stretch. The key difference between the two vibrations is the displacement of the central atom. Here we label the central atom as Mc and the two equivalent external atoms as M. The out-of-phase (asymmetric) stretch involves movement of all three atoms (see Fig. 5.1a) and the two vectors associated with the central mass reinforce one another (i.e., cooperate), resulting in larger movement of the central atom during the vibration. Characteristic phasing of the out-of-phase stretch is that one bond stretches while the other contracts. We can regard the middle atom as split into two halves moving with the same frequency and phase. Hence we consider the central atom, Mc, as 2 (M/2). Thus, the two oscillators of M e (M/2) vibrate at 180 out-of-phase with each other. The result of this is that the frequency of this type of vibration is strongly dependent on the mass of the central atom. We can extend the classical vibrational frequency definition presented earlier to the out-of-phase stretching vibration by splitting the central mass in half and the simple expression is: sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi rffiffiffiffi 1 2 Kpffiffiffi nop ¼ 1303 K þ ¼ 1303 3 m1 m2 m

63 64 5. ORIGIN OF GROUP FREQUENCIES

(a)

(b)

FIGURE 5.1 The stretching vibrations of a linear triatomic. The in-phase and out-of-phase stretches have been resolved into diatomic Me(N) and Me(M/2) components. The out-of-phase stretch is shown in diagram a and the in-phase stretch in diagram b. where K is the force constant and gives the restoring force for unit displacement from the m m equilibrium position, and 1 and 2 are the masses for the linear triatomic in Fig. 5.1. For three equivalent masses nop simplifies to the last term in the above equation. In the case of the in-phase (symmetric) stretch, the central atom does not move (see Fig. 5.1b). This is equivalent to the two exterior masses being connected to an infinite mass (N) where both mdN systems oscillate with same frequency and phase. In this case, the two spring force vectors exerted on the central mass oppose one another, resulting in no movement of the central atom during the vibration. Here, the frequency of this vibration is independent of the mass of the central atom in the symmetrical molecule and can be expressed classically as: sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi rffiffiffiffi 1 1 Kpffiffiffi n ¼ 1303 K þ ¼ 1303 1 ip m1 N m

Comparison of the above simple expressions predicts that the out-of-phase vibrations will be higher in frequency than the in-phase vibration. For a bent triatomic molecule, we ﬁnd that the frequencies of the in-phase and out-of- phase stretching vibrations are a function of the bond angle, a, between the three atoms.1,2 m We again consider the force vectors for the central atom 2 relative to the two exterior atoms, m m 1 and 3 for the in-phase and out-of-phase stretches. Figure 5.2 (lower left) shows the total restoring force tending to move the central atom along the right-hand bond. The restoring force vectors will by deﬁnition be opposite in sign from the Cartesian displacement vectors. For the in-phase mode, the forces act in opposition so there is less restoring force, while for the out-of-phase mode the forces cooperate resulting in more restoring force. The same analysis holds for the left-hand bond. The COUPLED OSCILLATORS 65

Restoring forces for in-phase and out-of-phase vibrations m m 2 C 2 C X axis m m C 3 S 3

m1 m1

Vector diagram for m2 atom

Cooperation

Opposition

In-phase KT, ip= K (1 + cos ) Out-of-phase KT, op = K (1 – cos )

FIGURE 5.2 The force diagrams for the central atom in a bent triatomic. The nature of the interaction of the two bond oscillators is a function of the bond angle, a. S and C indicate stretching and contraction of a bond and the bold arrows are the restoring forces. Both the in-phase (contract-contract) and the out-of-phase (stretch-contract) modes are shown. resultant mechanical coupling tends to lower and raise the in-phase and out-of-phase m em frequencies, respectively relative to that of the 2 3 diatomic model. Taking into account the bond angle dependence, we can calculate the frequency for the in- phase and out-of-phase stretching vibrations for bent triatomics. The out-of-phase stretch can be approximately calculated by: sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 1 cosa nop ¼ 1303 K þ m1 m2 where the bending force constant can be assumed to be zero. The in-phase stretch can be approximately calculated by: sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 1 þ cosa n ¼ 1303 K þ ip m1 m2

Here, we again neglect the bending force constant, but in this case it does contribute slightly. Figure 5.3 demonstrates the frequency dependence of triatomic in-phase and out-of-phase stretches on the bond angle, a. When a is greater than 90 , then the in-phase stretch is lower in frequency than the out-of-phase stretch, while a is less than 90 , then the in-phase stretch is higher in frequency than the out-of-phase stretch. Lastly, when a ¼ 90 the in-phase and out- of-phase stretches are equal because there is no mechanical interaction (vectors are orthogonal). An important extension of the above discussion is to consider the effects of mechanical coupling as a function of chain length.1,2 This is important since it applies to 66 5. ORIGIN OF GROUP FREQUENCIES linear aliphatic systems. Shown in Fig. 5.4 is a plot of vibrational frequencies for coupled CeC stretches of linear aliphatics as a function of increased chain length (i.e., 2,3,4. atoms) showing in-phase and out-of-phase vibrations. Standing waves are used to help describe the vibrations and their relative frequencies. For clarity, a plane (or node) separates the molecular segments, which vibrate out-of-phase with each other.

In-phase (symmetric) Out-of-phase (asymmetric) Opposition: lowers frequency Cooperation: raises frequency 180

opp coop )

90 opp

Bond angle ( coop

0 opp coop

Wavenumber (cm–1)

FIGURE 5.3 The frequency dependence of the in-phase and out-of-phase stretches of a triatomic molecule as a function of the bond angle, a. The arrows shown are displacement vectors.

1200 C S C S C ) –1 1100

C S uncoupled 1000

Wavenumbers (cm 900 S S S S S 800

1 bond 2 bonds 3 bonds Number of bonds

FIGURE 5.4 Plot of vibrations for coupled CeC stretch of linear aliphatics, as a function of increased chain length. COUPLED OSCILLATORS 67

B B B B ) 400 –1 N B B O Cooperation

300

Wavenembers (cm O B

O 200 Opposition BB

2 bonds 3 bonds 4 bonds Number of bonds

FIGURE 5.5 Plot of vibrations for coupled CeC bending vibrations of linear aliphatics, as a function of increased chain length. Note the out-of-phase vibration (opposition) is lower in frequency than the in-phase vibration (cooperation). Bending and open vibrations are indicated with B and O. No change in the bond angle is indicated by N.

Usually, the greater the number of nodes for stretching vibrations, the higher is the frequency. Figure 5.4 shows that a connection of several similar oscillators in linear chains results in as many chain frequencies as there are bonds. Thus, similar CeC, CeO, and CeN bonds will interact resulting in prominent IR and Raman bands. The relatively constant mechanical interaction gives results in group frequencies. Fortunately, for longer chains only a few of these vibrations provide important bands. We must also consider bending vibrations. The skeletal single-bond bending vibrations in aliphatic molecules vibrate at much lower frequencies than CeC stretches, CH stretch, or CH bending vibrations and generally fall in the far-IR region. The vibration involves mostly a deformation of the CeCeC bonds and the out-of-phase vibration is lower in frequency than the in-phase vibration. Figure 5.5 plots the vibrations for coupled CeC bending vibrations of linear aliphatics, as a function of increased chain length.

2. Rules of Thumb for Various Oscillator Combinations

For oscillator combinations of equal or nearly equal frequency both in-phase and out-of- phase oscillator combinations are involved.1,2 This simplest case considers equal oscillator combinations and includes stretchestretch and bendestretch vibrations. Some examples are shown in Fig. 5.6 and Table 5.1. 68 5. ORIGIN OF GROUP FREQUENCIES

–1 –1 CH2 = C = CH2 1071 cm CH2 = C = CH2 1980 cm

H H H H –1 –1 N 3300 cm N 3370 cm

R R

FIGURE 5.6 Examples of equal oscillator combinations.

TABLE 5.1 Examples of XY2 Type Identical Oscillators

XY2 Group Out-of-phase stretch In-phase stretch

e 1 1 R NH2 3370 cm 3300 cm e e 1 1 R CH2 R 2925 cm 2850 cm e 1 1 R CO2 1600 cm 1420 cm e 1 1 R NO2 1550 cm 1375 cm e e 1 1 R SO2 R 1310 cm 1130 cm

e e Examples of some two identical oscillator groups (non-linear M1 M2 M1) shown in Table 5.1 include: two hydrogen atoms on groups such as a methylene or primary amine and two oxygen atoms on groups such as carboxylate, nitro or sulfones. The XY2 group in the above can be considered approximately as an isolated oscillator since it has stretching frequencies signiﬁcantly higher than the frequencies of the CeC bond oscillators connected to it. As a result only the XY2 group atoms move appreciably during the stretching vibration. Because of this the above groups result in good group frequencies. The out-of-phase stretch is also an important IR group frequency for linear alkane alcohols, ethers, and primary and secondary amines.2 The vibration involves stretches of the CeC, CeO, or CeN bonds, which have very similar force constants. The frequencies shown below support this. 1 CH3 CH3 992 cm 1 CH3 OH 1033 cm 1 CH3 NH2 1036 cm Consequently, stretches involving CeC, CeO, and CeN will strongly couple giving rise to skeletal out-of-phase stretching vibrations in the following general spectral regions: 1 C C Ow1050 cm 1 C O Cw1125 cm 1 C C Nw1080 cm 1 C N Cw1140 cm COUPLED OSCILLATORS 69

H B B

XYS

Amide CNH str./bend S 1550 cm–1 Cooperation: higher frequency

H O O

X S Y

Amide CNH str./open S 1250 cm–1 Opposition: lower frequency

FIGURE 5.7 The stretchingebending interaction for the HeXeY group. S stands for stretch, B for bend, and O for open. The approximate band position is also included for the amide group CNH stretch/bend and stretch open vibrations.

The CeCeO and CeOeC species in particular give good strong IR group frequencies as a result of a relatively constant interaction with other CeC bonds. Figure 5.7 shows the second type of important equal oscillator vibration, the bend-stretch vibration.2 Mechanical coupling of bending and stretching vibrations can occur if both are of nearly equal frequency. In this case, we consider a simple bent HeXeY oscillator where both X and Y are heavier than the hydrogen. The HeX bending frequency may be nearly identical to that of the XeY stretching frequency, allowing the two oscillators to couple. Two vibrations result involving the XeY stretch and the HeXeY bend which differ only in the relative phases. An example of this is the amide group where X ¼ nitrogen and Y ¼ carbon. The HeX stretching oscillator has much higher frequency than the XeY stretching oscillator and is therefore an isolated vibration (see below for rules for unequal oscillators). As shown above, there are three components for this molecular vibration: the rotation of the XeY bond, the stretching of the XeY bond, and the rotation of the HeX bond. Here, the rotation of the XeY bond has little effect since the vectors involved are orthogonal (i.e., 90 ) with respect to both the XeY stretch and the HeX rotation. However, rotation of the HeX bond results in movement of the X atom either in the same or in opposite direction that it moves during the XeY stretch. The bend/stretch involves cooperation of the X atom vectors 70 5. ORIGIN OF GROUP FREQUENCIES

1. High frequency: only atoms of high frequency component move appreciably. Cl C C C C C O H C H C C N C O s s c s s C s C

2. Low frequency: only the bond length or angle of low frequency component changes appreciably. H O C C C H C C N O C Cl C C s O s s s s

FIGURE 5.8 Examples of unequal oscillator combinations. and thus higher frequency while the bend/open involves opposition of the X atom vectors and thus lower frequency. Oscillators with different frequencies have two important approximate rules of thumb: 1. In high frequency vibration of the combination, only atoms of the high frequency component move. 2. In low frequency vibration of the combination, only the bond length or angle of the low frequency component changes. Some simple examples of typical unequal oscillator combinations encountered are shown in Fig. 5.8. Lastly, for systems containing more than two equal oscillators, the resulting vibrations can become much more complex and standing waves can be used to simplify the description of the vibrations.2 An excellent example of this is the stretching vibrations for a benzene ring. Figure 5.9 shows the standing vibrational waves employed to describe the stretching vibrations of six-membered rings.

C S S C S C S C C C S C S S C C S S S

1 2a 2b3a 3b4

FIGURE 5.9 Standing vibrational waves for stretching vibrations of six-membered rings. COUPLED OSCILLATORS 71

Chapter 5: Questions 1. Using the mathematical expression for a harmonic oscillator, calculate the force constant, K, for the following species: CH 3000 cm 1, NH 3400 cm 1,OH3600cm 1. Note that H ¼ 1 amu, C ¼ 12 amu, O ¼ 16 amu, and N ¼ 14 amu. What are the possible sources of the observed variation in the frequencies for the above? 2. The following ethers have bands associated with the in-phase and out-of-phase CeO stretching vibrations: 1100, 810 cm 1 1080, 890 cm 1 1020, 990 cm 1 1220, 890 cm 1. Using a scatter plot of frequency versus bond angle, explain the origin of the observed trends.

1100, 810 cm-1 1080, 890 cm-1 1020, 990 cm-1 1220, 890 cm-1

O O O O

3. Calculate the in-phase and out-of-phase stretching frequencies for six and four membered cyclohexane, cyclopropane, and cyclobutane rings. Here k ¼ 4.2 mdynes/ A and M ¼ 14 amu for the methylene group. The in-phase ring stretch frequency equation is: y ¼ 1303½kð1 þ cosaÞðM þ 1=M Þ1=2 ¼ ½k=M1=2 a= ip 1 2 1303 2cos 2

Ring Size a (deg) In-phase stretch (exp) Calculated

N ¼ 6 109.5 802 N ¼ 5 104 886

N ¼ 4 90 1003

4. Calculate the in-phase and out-of-phase stretching frequencies for the following XY2 e e e groups: R NH2 (6.4 mdynes/A), R CH2 R (4.9 mdynes/A). 5. Provide a summary of the general types of vibrations encountered. In general, where in the vibrational spectrum will these vibrations be found? 6. The bending vibration for propane is observed at 375 cm 1 while for butane it is observed at 427 and 271 cm 1. Draw the vibrations and explain the frequency differences. 7. Suggest other possible functional groups beyond those listed in table 5.1 that would ﬁt the XY2 type identical oscillators. 72 5. ORIGIN OF GROUP FREQUENCIES References

1. Infrared and Raman Spectroscopy, Methods and Applications; Schrader, B., Ed.; VCH: New York, NY, 1995. 2. Colthup, N. B.; Daly, L. H.; Wiberley, S. E. Introduction to Infrared and Raman Spectroscopy, 3rd ed.; Academic: New York, NY, 1990. 3. Barrow, G. M. Introduction to Molecular Spectroscopy; McGraw-Hill: New York, NY, 1962. CHAPTER 6

IR and Raman Spectra-Structure Correlations: Characteristic Group Frequencies

In the following chapter we include generalized Infrared and Raman spectra of selected regions which illustrate the generalized appearance of bands for selected characteristic group frequencies. In each case, the upper spectrum shows the transmission infrared spectra with bands pointing downward and the lower spectrum shows the Raman spectrum with bands pointing up. The vertical axes are expressed in percent infrared transmission and Raman intensity. We also describe the approximate forms of selected vibrations and include tables summarizing important bands and their assignments.

1. XeH STRETCHING GROUP (X[O, S, P, N, SI, B)

The set of spectra in Fig. 6.1, illustrates some useful XeH stretching bands. The large differences in XeH stretching frequencies are mostly due to differences in bonding and therefore the force constants. Quite often these bands are more intense in the IR than in the Raman spectra.1-4 As shown in the top two spectra in Fig. 6.1, the OH stretch is particularly weak in the Raman but strong in the IR. The hydrogen-bonded alcoholic OH stretch vibration gives rise to a broad band near 3350 cm 1 in the IR spectrum. A more strongly hydrogen-bonded OH in a carboxylic acid dimer has a much broader band centering about 3000 cm 1.An exception to this is the SH group of a mercaptan which gives rise to a sharp weak IR band and a strong Raman band at about 2560 cm 1. 1 Aliphatic primary amines have a weak NH2 doublet in the IR near 3380 and 3300 cm which derive from the out-of-phase and in-phase NH2 stretching vibrations, respectively. The weak shoulder observed near 3200 cm 1 is the Fermi-resonance enhanced overtone 1 of the 1620 cm NH2 bend. Typically, the in-phase NH2 stretch is stronger in the Raman ¼ e spectra than the out-of-phase stretch. In primary amides, O C NH2, bands involving the 1 NH2 stretches are found at 3370 and 3200 cm , and are typically stronger in the IR than e in the Raman spectra. The PH2 group gives rise to a medium weak single band in both the IR and Raman spectra near 2280 cm 1.

73 74 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

FIGURE 6.1 The generalized IR and Raman spectra of selected XeH stretching bands, where X ¼ oxygen, sulfur, phosphorus, nitrogen, or silicon.

Secondary aliphatic amines have a NH stretch band near 3300 cm 1 which is quite weak in the IR but stronger in the Raman spectrum. Monosubstituted amides, O¼CeNHe, have a stronger IR band near 3300 cm 1 which derives from the NH stretch. An additional weak band near 3100 cm 1 is the overtone of the 1550 cm 1 CNH stretch/bend. The last group 1 shown is SiH2 species that has a single band at ca. 2130 cm which is quite strong in the IR but weak in the Raman. e Although not shown in Fig. 6.1,B OH and BH/BH2 are characterized by moderate to strong IR OH and BH stretching bands but weak Raman bands. The BeOH group has a strong 1 broad band between 3300 and 3200 cm from the OH stretching vibration. The BH and BH2 e 1 groups have moderate to strong IR bands in the 2630 2350 cm region. The BH2 group has e 1 e 1 both an out-of-phase (2640 2570 cm ) and in-phase (2532 2488 cm )BH2 stretching bands. Fully annotated IR and Raman spectra of selected carboxylic acids (#24e27), amides (#30e32), alcohols (#40e47), boronic acid (64), and amines (#51e53) are included in the last section for comparison.

2. ALIPHATIC GROUPS

The set of spectra in Fig. 6.2 illustrate some selected group frequencies for alkane groups.1-4 The group frequencies are also summarized in Table 6.1. Figure 6.3 illustrates the vibrations of 1-4 the methylene (CH2) group. For the non-cyclic (CH2)n chain, the CH2 out-of-phase and the 1 in-phase stretching bands are near 2930 and 2855 cm , respectively, and the CH2 bend (defor- 1 mation) band is near 1465 cm . For the methylene segments (CH2)n in the trans zig-zag form, ALIPHATIC GROUPS 75

FIGURE 6.2 The generalized IR and Raman spectra of linear and branched alkane groups. The spectral components from methyl and methylene groups have been separated in the top two rows of spectra. The bottom row illustrates the sensitivity of IR and Raman spectra to branching in alkane group.

1 the in-phase CH2 twist is observed near 1300 cm in the Raman spectrum, and the in-phase 1 (CH2)n rock is found near 723 cm in the IR. Figure 6.4 illustrates the vibrations of the CH3 group. For the CH3 group on an alkane carbon, bands near 2960 and 2870 cm 1 derive from the out-of-phase and in-phase stretches and the out-of-phase bend results in a band at ca. 1465 in the IR. The in-phase bend of a single 1 CH3 on an alkane carbon results in a band near 1375 cm in the IR. The presence of an adjacent group such as a N or O atom can result in a signiﬁcant frequency shift in the methyl 1 (CH3) in-phase stretch to lower frequency between 2895 and 2815 cm . When there are two methyl groups on one carbon such as an iso-propyl or a gem-dimethyl group, this splits into two nearly equal intense bands near 1385 and 1365 cm 1 in the IR. When there are three methyl groups on one carbon, such as a tertiary-butyl group, there is further splitting into a weak band at ca. 1395 cm 1 and a stronger band near 1365 cm 1 in the IR spectrum. In addition, for these groups there are strong Raman bands at ca. 1 1 800 cm which involves the in-phase stretch of the C(C3) group and at ca. 700 cm for the in-phase stretch of the C(C4) group. However, although intense, this Raman band will vary considerably in frequency due to strong mechanical coupling with attached CeC, CeO, CeNorCeS groups. Table 6.2 summarizes this variation for a few selected 76 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

TABLE 6.1 Selected Group Frequencies: Aliphatics

Intensities1 Group Assignment Frequency (cmL1) IR R

CH e 2 e 3 R CH3 o.ph. str. 2975 2950 vs vs ” i.ph. str. 2885e2860 vs vs ” o.ph. bend 1470e1440 ms ms ” i.ph. bend 1380e1370 m vw e e R CH(CH3)2 bend-bend 1385 1380 m vw ” bend-open 1373e1365 m vw e R(CH3)3 bend-bend 1395 1385 m vw ” bend-open 1373e1365 ms vw þ e aryl-CH3 i.ph. str. 2935 2915 ms ms ” bend overtone 2875e2855 m m e e e R O CH3 i.ph. str. 2850 2815 m m ” i.ph. bend 1450e1430 ms m e e R2N CH3 i.ph. str 2825 2765 s s ¼ e e O C CH3 i.ph. bend 1380 1365 s w CH e e 3 e 2 R CH2 R o. ph. str. 2936 2915 vs vs ” i. ph. str. 2865e2833 vs vs ” Fermi resonance 2920e2890 w m

” bend 1475e1445 ms ms e e (CH2)>3 i.ph. twist 1305 1295 m e e (CH2)>3 i.ph. rock 726 720 m ¼ e e O C CH2 bend 1445 1405 m m h e e N C CH2 bend 1445 1405 m m e e O CH2 wag 1390 1340 m m e e Cl CH2 wag 1300 1220 m m CH e R3CH CH bend 1360 1320 w w O¼CeH CH str. þ 2900e2800 m m ” rk overtone 2770e2695 m m ” CH rock 1410e1380 m m

1s ¼ strong, m ¼ medium, w ¼ weak, v ¼ very, br ¼ broad, var. ¼ variable, e ¼ zero 2o.ph. str. ¼ out-of-phase stretch, i.ph. str. ¼ in-phase stretch, rk ¼ rock 3 e 1 Note: In the trans zig-zag segments of the long chain (CH2)>6 group, the Raman active CH2 out-of-phase stretch band is at 2900 2880 cm (2883 cm 1 in polyethylene). The gauche segments have this at 2936e2916 cm 1 in the Raman. ALIPHATIC GROUPS 77

Nodal plane O O O O O O

S O S O S O C O O B O O O O

CH2 CH2 CH2 Out-of-phase stretch In-phase stretch Bend

O O O O O – + O O O O O O O O O O

CH2 Wag CH2 Twist CH2 Rock

FIGURE 6.3 Vibrations of the CH2 group. C and S stand for contract and stretch, and B and O stand for bend and open. Movement of atoms are depicted by arrows or by þ and signs if the atom movement is out of the page. Nodal planes are used to help differentiate the vibrations. compounds. Fully annotated IR and Raman spectra of selected aliphatic compounds are included in the last section of fully interpreted spectra for comparison (#1e3). In Fig. 6.5, the relative intensities in the IR and Raman spectra in CH stretching region are illustrated for some selected alkanes. The vibrations involving the methyl and methylene stretches (3000e2800 cm 1) give rise to bands that are strong and characteristic in both the IR and Raman spectra but show greater complexity particularly in the Raman spectra due to Fermi-resonance effects.5,6,7 The CH stretching region of the IR and Raman spectra shows additional bands due to Fermi resonance between the methylene CH stretching vibrations and the overtone of the methylene bending (deformation) vibrations (1480e1440 cm 1). Bands observed in the 2900 cm 1 region as a weak shoulder in the IR spectrum and as more isolated and obvious bands in the Raman spectra derive from Fermi resonance. This occurs in the IR and Raman spectra of aliphatics when: 1. There are at least two almost equivalent neighboring methylene groups. 2. The symmetry and frequency of the methylene CH2 stretch and the CH2 deformation overtone is suitable for Fermi resonance. The above results in multiple Fermi-resonance doublets associated with the methylene group including the broad bands observed in the 2920e2898 cm 1 region and results in signiﬁcantly more complicated Raman spectra of n-alkanes as observed in Fig. 6.5. 78 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

Nodal plane O O s O c O O O O O O O s O O O O c O s s s s

CH3 Out-of-phase stretch CH3 In-phase stretch

O o o O O o o O B O O B O O O O O O O O O o B

CH3 Out-of-phase bend CH3 In-phase bend

o B O O O O o O O O O O O O O O O O B

CH3 Rock CH3 Torsion

FIGURE 6.4 Vibrations of the CH3 group. Nodal planes are used to differentiate between doubly degenerate vibrations. C and S stand for contract and stretch, and B and O stand for bend and open.

The conformational equilibrium of n-alkanes due to rotation about the CeCbondof the long chain aliphatic can also affect the IR and Raman spectra in the gas phase or in pressure induced transitions. Thus, for n-Pentane these conformations would include methylene in the all-trans (TT a planar zig-zag form), single gauche (TG), and double gauche (GG) conformers.8 The methylene and methyl stretching bands are sensitive markers of these different conformers. The all trans conformation is typically found in the condensed state under ambient room temperature conditions such as shown in Fig. 6.5. The relative IR intensities of the methyl and methylene bands can be used to estimate the relative concentration of the two species. In the case of the IR spectra in Fig. 6.5, the methyl 1 (CH3) out-of-phase stretch at ca. 2960 cm is doubly degenerate and is therefore twice as 1 intense at the methylene (CH2) out-of-phase stretch at 2925 cm . Using this relationship, the relative amount of methyl and methylene group can be rapidly estimated from the IR spectrum. CONJUGATED ALIPHATICS AND AROMATICS 79

TABLE 6.2 Summary of the Raman In-Phase CeC/CeX Stretching Band for Selected Compounds, where X is Carbon, Nitrogen, Oxygen or Sulfur

X-Element CeCeCeX (i.ph.str.) (C)2CeX (i.ph. str.) (C)3CeX (i. ph. str.)

Carbon (12) 827 cm 1 800 cm 1 733 cm 1

CH CH3CH2CH2CH3 CH3 3

CH H3C CH H3C 3

CH CH3 3

Nitrogen (14) 868 cm 1 802 cm 1 748 cm 1

CH3 CH3 NH2 H N CH 2 H3C NH2

CH3 CH3

Oxygen (16) 822 cm 1 819 cm 1 750 cm 1

CH3 CH3 OH HO CH H3C OH CH3 CH3

Sulfur (32) 670 cm 1 631 cm 1

CH3 SH HS CH

CH3

3. CONJUGATED ALIPHATICS AND AROMATICS

Selected IR and Raman characteristic frequencies of conjugated aliphatics and aromatics are summarized in Table 6.3.1-4 Included are triple and cumulated double bond species, oleﬁnics, and aromatics. Three sets of generalized IR and Raman spectra also illustrate some of the characteristic bands for these species. Below, we discuss oleﬁnics, triple and cumulated double bonds and aromatics in more detail. Bonds Triple spectra. n Group 6.3 TABLE 6.5 FIGURE 80 -heptane, Relative intensity %Transmittance 100 0.0 2.0 80 1.0 3.0 60 20 40 .I N AA PCR-TUTR ORLTOS HRCEITCGOPFREQUENCIES GROUP CHARACTERISTIC CORRELATIONS: SPECTRA-STRUCTURE RAMAN AND IR 6. n otn,adccoeae diinlbnsdet em eoac r lal bevdi h Raman the in observed clearly are resonance Fermi to due bands Additional cyclohexane. and -octane, n -Pentane eetdGopFeunis rpeBns uuae obeBns ojgtdAihtc and Aliphatics Conjugated Bonds, Aromatics Double Cumulated Bonds, Triple Frequencies: Group Selected CH

h nrrdadRmnsetai h Hsrthn einaeilsrtdfor illustrated are region stretching CH the in spectra Raman and infrared The 2963 2966 2935 2938 ”C C CH ” ”C conj-C C S 2914 3 e e e 2876 2879 C C C 2 CH CH e h h h CH C h NC 2 2 C C h 3 NC e e NC H CC n -Hexane

2963 2962 CH 2938 2917 2926 3 2875 2874 2863 2860 CH CH CH 2 2 3 Hstr. CH Assignment Hwag CH h h h h h H Wavenumber (cm 2 str. C t.2260 str. N str. C str. N str. N bend n -Heptane

2962 2959 CH 2937 2926

2904 2874 3 2875 2863 2858 CH CH CH 2 2 3 –1 ) n 3340 rqec (cm Frequency 2140 1440 2245 710 2235 2170 -Octane 2962 2959 CH e 2936 e e e e e e e 2925 578

2898 3 3267 2100 2240 1405 2100 2185 2135 2875 2873 2853 2856 CH CH CH 2 3 2 L 1 n ) -pentane, Cyclohexane w s RR IR vs w vs m m m e ,rw s,br a.s var. ss ms Intensities CH 2938 2930 2924 2897 2 n 2853 2852 -hexane, CH s

1 CONJUGATED ALIPHATICS AND AROMATICS 81

TABLE 6.3 Selected Group Frequencies: Triple Bonds, Cumulated Double Bonds, Conjugated Aliphatics and Aromaticsdcont’d

Intensities1 Group Assignment Frequency (cmL1) IR R

Cumulated > ¼ ¼ e C C CH2 CCC o.ph. str. 2000 1900 vs vw Double eN¼C¼O NCO o.ph. str. 2300e2250 vs vw Bonds eN¼C¼S NCS o.ph. str. 2200e2000 vs mw C¼C C¼C mono, cis, 1,1 C¼C str.2 1660e1630 m s Alkane Subst. C¼C trans, tri, tetra C¼C str.2 1680e1665 weos

C¼CHeR mono, cis, trans CH str. 3020e2995 m m ¼ e C CH2 mono, 1,1 CH2 o.ph. str. 3090 3075 m m e ”CH2 i.ph. str. 3000 2980 m s e ”CH2 bend 1420 1400 w m e ¼ e R CH CH2 trans CH i.ph. wag 995 985 s w ¼ 3 e ” CH2 wag 910 905 s w ¼ ¼ 3 e R2C CH2 CH2 wag 900 885 s w ReCH¼CHeR trans ¼CH i.ph. wag 980e965 s e ReCH¼CHeR cis ¼CH i.ph. wag 730e650 ms e e ¼ ¼ e R CH CR2 CH wag 840 790 m Aromatics aryl CH CH str. 3100e3000 mw s ring quadrant str. 1620e1585 var m

” quadrant str. 1590e1565 var m ” semicircle str. 1525e1470 var vw ” semicircle str. 1465e1400 m vw mono, meta, 1,3,5 2,4,6 radial i.ph str. 1010e990 vw vs meta, 1,2,4 & 1,3,5 lone H wag 935e810 m e para and 1,2,4 2 adj. H wag 880e795 s e

meta and 1,2,3 3 adj. H wag 825e750 s e ortho and mono 4 & 5 adj. H wag 800e725 s e mono, meta, 1,3,5 ring out-of-plane bend 710e665 s e para ring in-plane bend 650e630 e m mono ring in-plane bend 630e605 w m

1s ¼ strong, m ¼ medium, w ¼ weak, v ¼ very, br ¼ broad, var. ¼ variable, e ¼ zero 2 ¼ e 1 h e ¼ 1 Conjugation lowers C C frequencies 10 50 cm (e.g., N C CH CH2 1607 cm ) 3 ¼ e e ¼ 1 Electron donor substituents lower the CH2 wag frequencies (e.g., R O CH CH2 813 cm ) and electron withdrawers raise them (e.g., h e ¼ 1 N C CH CH2 960 cm ) 82 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES 3.1. Alkyl-Substituted Oleﬁnic Groups

The set of IR and Raman spectra in Fig. 6.6 illustrate selected group frequencies for the ethylene C¼C groups with alkane group substituents.1-4 Particularly, useful Raman bands ¼ ¼ ¼ for the olefinic group include the CH stretch, in-phase CH2 stretch, and the C C stretch. In the IR spectra, the olefinic out-of-plane CH and CH2 wag are quite important. Figure 6.7 illustrates the in-plane olefinic vibrations and Fig. 6.8 summarizes the observed and estimated C¼C stretching frequencies for fifteen different compounds containing an olefinic group. The out-of-plane CH wag vibrations are shown in Fig. 6.9. The in-plane vibrations of the olefin group are depicted in Fig. 6.7.Thevinyland ¼ ¼ 1,1-disubstituted ethylenes have a CH2 group with CH2 out-of-phase and in-phase stretching bands near 3080 and 2985 cm 1,respectively.The¼CH group in vinyls, cis, trans 1,2-disubstitituted ethylenes, and trisubstituted ethylenes all have a ¼CH stretching band at ca. 3010 cm 1. The vinyl, 1,1-disubstituted, and 1,2-cis disubstituted ethylenes all have aC¼C stretch with strong intensity in the Raman and medium intensity in the IR. In the case of 1,2 trans disubstituted, tri-substituted, and tetra-substituted ethylene groups, the C¼C stretch at ca. 1670 cm 1 is quite strong in the Raman but weak or absent in the IR. The frequency of the C¼C stretch will vary depending on the nature of the substituent. Conjugation effects tend to be particularly important, usually lowering the C¼C stretching frequency. The selected compounds in Fig. 6.8 vary in the cyclic olefinic structures and most impor- tantly the CeC¼C bond angle. Mechanical coupling of the stretching vibrations of bonds attached to olefinic groups is the critical variable in determining C¼C stretching fequencies in cyclic olefin species.1 The calculated frequencies are from an adapted form of the triatomic model discussed earlier and includes mechanical coupling of the CeCstretch

FIGURE 6.6 Generalized IR and Raman spectra of alkyl-substituted oleﬁns. CONJUGATED ALIPHATICS AND AROMATICS 83

O O R–CH=CH2 1662–1631 cm–1 R2C=CH2 R–CH=CH-R Cis OO C=C str O R–CH=CH-R Trans –1 O R2C=CH–R 1692–1665 cm R2C=CR2 O O

–1 O CH2 Out-of-phase str. 3080 cm

OO –1 CH2 In-phase str. 2990 cm O

O O –1 O CH Str. 3020 cm

OO –1 CH2 Bend 1415 cm O

O O Cis –1 O O CH rock 1415 cm O O

FIGURE 6.7 The olefin in-plane vibrations are shown above. Arrows depict the movements of atoms. with the C¼C stretch. The model uses force constants for the C¼C and attached CeCof8.9 and 4.5 mdynes/A, respectively, neglects the bending force constants, and includes the CeC¼C bond angle. The approximate form of the model describing the total forces on the olefinic group for the external and internal C¼C group are shown on the left side of Fig. 6.8. Despite their simplicity, these calculations are successful in predicting trends in the frequencies in the top two rows. This data demonstrates that little or no change in the C¼C force constant is required to explain the observed frequency shifts when one or both of the olefinic carbon atoms are part of a ring. No calculations are shown for the bottom row, but the experimental data indicates that for ring sizes between four and six, the effects of the indicated changes in both the external and internal CeC¼C bond angles approximately cancel each other, resulting in similar C¼C stretching frequencies. The critical importance that mechanical effects has in determining the C¼C stretching frequencies in cyclic olefin structures has similarly been demonstrated using vibrating ball bearing and coil spring molecular models.9 84 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

F2 HH HH HH HH F1 HH C C C C C 120 126 135 150 180 C F2 C HH Calc (cm–1) 1639 1661 1696 1756 Obs (cm–1) 1651 1657 1678 1736 1957

F1 HHHHHHHH HHCC 120 108 90 60 0 F2 F2

Calc (cm–1) 1636 1606 1587 1636 1776 Obs (cm–1 ) 1646 1611 1566 1656 1974

120 135 150 180 RRRR126 RRR R R CCR 120 108 90 60 0

Obs (cm–1) 1681 1678 1675 1883 2250

FIGURE 6.8 The cyclic C¼C stretching frequencies as a function of the CeC¼C bond angles. The calculated frequencies used force constants F1 and F2 values of 8.9 and 4.5 mdynes/A, respectively. The simple model used to calculate the frequencies is summarized on the left-hand side of the ﬁgure.

– – O O O O +O O + + + + – – + OO–– OO OO O O O – O + O + +O Vinyl Vinyl Vinyl trans cis CH wag =CH2 wag CH wag

O O O O O O + ++ + – – – – OO – + OO O O O O+ O O + ++O O 1,2-Trans-disubst 1,1-disubst 1,2-Cis-disubst Cis trans CH wag =CH2 wag CH wag

FIGURE 6.9 The out-of-plane CH wag vibrations of the oleﬁnic group are shown above. Movement of atoms are depicted by arrows or by þ and signs.

The CH wag bands (see Fig. 6.9) are strong in the IR and highly characteristic of the alkyl substitution on the ethylene C¼C group. These alkyl-substituted oleﬁnic CH wag bands are observed near 990 and 910 cm 1 for vinyl groups, near 890 cm 1 for 1,1-disubstitution, near 970 cm 1 for trans 1,2-disubstitution, and roughly at 680 cm 1 for cis 1,2-disubstitution. The nature of the substituent can result in large but predictable frequency shifts of the oleﬁnic CH ¼ and CH2 wag. The CH2 wag is sensitive to electronic changes and shows a linear frequency dependence based upon experimentally determined substituent Hammet constant as well as CONJUGATED ALIPHATICS AND AROMATICS 85

0.8 –COOH –CHO 0.6 –CN O

= s–trans –C–CH3 0.4 O s–cis

= –phenyl O –CF3

–O–C–CH3 = –C–OCH 0.2 3

Hammet constant 0.0 –F –CH3 –O–CH3 Cis Gauche – 0.2

– 0.4 800 820 840 860 880 900 920 940 960 980 Wavenumber (cm–1)

FIGURE 6.10 Correlation of the Hammet constant of substituents of mono-substituted ethylene with the CH2 wag frequency. the calculated substituent electronegativity and the electron density on the carbon atom.10,11 ¼ Figure 6.10 shows the linear dependence for the mono-substituted ethylene CH2 wag as a function of the intrinsic electronic contribution to the Hammet values.11 These well-defined trends of the frequency dependence of the CH wag vibrations on the substituent properties are also observed in more highly substituted olefinic groups.1 For example, substitution of an electron withdrawing ester group (eCOeOeR) in the XYC ¼ CH2 species will raise the frequency of the CH2 wag. Similarly, substitution of an electron donating ether group (eOR) will lower the frequency. The trans CH wag shows a predictable frequency dependence upon the substituent electronegativity. An increase in the substituent electronegativity relative to an aliphatic will lower the CH wag frequency. Fully annotated IR and Raman spectra of selected olefinic compounds are included for comparison in the last section (#4e6, and 31e32).

3.2. Triple and Cumulated Double Bonds

Figure 6.11 illustrates some of the characteristic bands for ChC, ChN, and the X¼Y¼Z groups.1-4 The CeChCeH group has a CH stretch band near 3300 cm 1 and a hCeH wag band near 630 cm 1 which are both strong in the IR and weak in the Raman. The ChC stretch band is found at ca. 2125 cm 1, which is weak in the IR but strong in the Raman. The symmetrically substituted ChC stretching vibration is IR inactive but Raman allowed. For the dialkyl acetylenes, the Raman spectra usually has two bands near 2300 and 2230 cm 1 resulting from Fermi resonance splitting of the ChC stretch. For the diaryl acetylenes, only a single ChC stretch band is observed in the Raman near 2220 cm 1. The ReChN group results in IR and Raman ChN stretch bands near 2240 cm 1 which can be lowered by roughly 20 cm 1 by conjugation with a suitable substituent. The eSeChN 86 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

FIGURE 6.11 Generalized IR and Raman spectra of selected triple and cumulated double bond compounds.

group is characterized by IR and Raman bands near 2150 cm 1 which involve the ChN stretch. The eN¼C¼O, eN¼C ¼S, and eN¼C¼N e groups all have very strong IR bands in the 2280e2050 cm 1 region resulting from an out-of-phase stretch of the X¼Y¼Z bonds. Fully annotated IR and Raman spectra of two selected nitrile containing compounds as well as an acetylene compound are included in the last section for comparison (#7e9).

3.3. Aromatic Benzene Rings

The twenty different normal modes of benzene are shown in Fig. 6.1212. A simple substitution of only one substituent results in a signiﬁcant increase in the modes of vibration to thirty. Table 6.4 provides the calculated and experimental frequencies along with the unique Wilson numbers and accompanying symmetry for the modes of vibration for benzene.13 As shown in Fig. 6.12, the benzene CeH stretching vibrations are observed in the 3100e3000 cm 1 region. In all other vibrations below 3000 cm 1 the CeH bond length remains relatively unchanged. Many of the bands observed in the 1600e1000 cm 1 region involve in-plane CeH bending vibrations that interact with various ring C¼C vibrations. Out-of-plane CeH bending (i.e., wag) vibrations give rise to bands below ca. 1000 cm 1. In general, many of the aromatic ring vibrational modes are insensitive to the substituent groups and can be regarded as good group frequencies for the benzene ring. Some of the vibrations are substituent sensitive and result in mechanical coupling with the substituent group vibrations and can provide important structural information. However, not all of these CONJUGATED ALIPHATICS AND AROMATICS 87

2 20a 20b 7a 7b

3073 cm-1 3064 cm-1 3064 cm-1 3056 cm-1 3056 cm-1

13 8a 8b 19a 19b

3057 cm-1 1599 cm-1 1599 cm-1 1482 cm-1 1482 cm-1

3 14 9a 9b 15

1350 cm-1 1309 cm-1 1178 cm-1 1178 cm-1 1146 cm-1

+ - - 18a 18b 12 1 5 + + - 1037 cm-1 1037 cm-1 1010 cm-1 993 cm-1 990 cm-1 + - - + - - - + + + - + - + - - + - - - + + 17a 17b 10a 4 + - + - 10b - - - + - - - - + + - + - + - + + + 967 cm-1 967 cm-1 846 cm-1 846 cm-1 707 cm-1 - + - - + + - - - + - 6a - - 11 6b -16a + -16b - - - - + - + - - + 673 cm-1 606 cm-1 606 cm-1 398 cm-1 398 cm-1

FIGURE 6.12 Approximate vibrational modes of benzene adapted from (M.A. Palafox, Int. J. Quant. Chem., 77, 661e684, 2000). The electronic structure was determined using density functional method with a6e31G* basis set. Out-of-plane molecular vibrations are depicted using þ and to indicate out of and into the page, respectively. 88 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

TABLE 6.4 Calculated and Experimental Frequencies for the Normal Ring Modes of Benzene

Frequency (cmL1) Wilson no. Symmetry Calc IR (Liquid) IR (Gas) Description

d 1a1g 1026 993 993.1 (CCC) n e 2a1g 3218 3073 3073.9 (C H) d e 3a2g 1375 1350 1350 (C H) g 4b2g 719 707 707 (CCC) g e 5b2g 1015 990 990 (C H) g 6e2g 618 606 608.1 (CCC) n e 7e2g 3192 3056 3056.7 (C H) n ¼ 8e2g 1664 1599 1600.9 (C C) d e 9e2g 1203 1178 1177.8 (C H) g e 10 e1g 866 846 847 (C H) g e 11 a2u 694 673 673.9 (C H) d 12 b1u 1013 1010 1010 (CCC) n e 13 b1u 3182 3057 3057 (C H) n ¼ 14 b2u 1378 1309 1309.4 (C C) d e 15 b2u 1178 1146 1149.7 (C H) g 16 e2u 412 398 398 (CCC) g e 17 e2u 978 967 967 (C H) d e 18 e1u 1071 1037 1038.3 (C H) n ¼ 19 e1u 1524 1512 1483.9 (C C) n e 20 e1u 3208 3064 3064.4 (C H)

The data is from (International J of Quantum Chemistry, 77, 661e684, 2000) and includes calculated frequencies used density functional method with a 6e31G* basis set and experimental values vibrations are of use since many are either weak or absent in either the IR and Raman spectra. The vibrational modes of the aromatic benzene ring that are sensitive to the mass and electronic properties of ring substituents include the following: 1. 1300e1050 cm 1 region, involving in-plane movement of the ring carbons and the substituents. 2. 850e620 cm 1 region, involving the CH wag vibrations (intense in IR but weak in Raman) and ring out-of-plane vibrations. Some of the characteristic group frequencies for mono- and di-substituted benzenes are illustrated in the generalized IR and Raman spectra depicted in Fig. 6.13.1-4,14 Many different types of aromatic ring vibrations are illustrated which demonstrate how IR and CONJUGATED ALIPHATICS AND AROMATICS 89

FIGURE 6.13 Generalized IR and Raman spectra of mono- and di-substituted benzenes. The complex ring vibrations can be greatly reduced using a standing wave description. This technique allows easy visualization of the form of the ring vibrations.

Raman spectra can be used to characterize aromatic substitution types. Useful group frequencies include the following: • CH stretch bands • Ring stretch bands • Ring bend bands • CH rock and CH wag bands • Aromatic summation bands Figure 6.14 shows the form of the 12 elementary vibrations for a six-membered ring with equal bond lengths, masses, and no substituents. The vibrational standing waves for these vibrations are also shown.1,4 The top row illustrates the six ring stretching vibrations and the bottom row the six bending vibrations for this simple six-membered ring. The dashed lines show the nodal lines used to deﬁne the sextant , quadrant, semicircle, or whole ring vibrations. These lines separate molecular segments which vibrate out-of-phase with each other. The doubly degenerate ring modes are labeled with subscripts “a” and “b”. Bands originating from ring vibrations in the IR and Raman spectra shown in Fig. 6.13 are annotated using the above description. The bottom row indicates the accompanying motion of the attached hydrogens in benzene which mechanically couple with the above ring modes. The aryl CH stretch bands are observed in the 3100e3000 cm 1 region. The IR spectrum usually has several bands here while the Raman usually has only one. The ring quadrant stretch vibration has two components observed in the IR and Raman spectra near 1600 90 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

C S S C S C S C CC S C S C S S S C S

4 3a 3b2a 2b1

+ + O B O O B O – –––+ – B B + + –– – + B O B O O B – +

65a 5b87a7b

Modes 1 & 6 mix in mono, meta- and 1,3,5 substituted ring

1-6 1+6 _ Attached + hydrogen H H H H H H motions in C C C C benzenes C C+ + Above ~3000 Below ~3000 Above ~1250 Below ~1250 Above ~710 Below ~710 CH stretch CH bend CH wag Carbon radial Carbon tangential Carbon out-of-plane

FIGURE 6.14 The twelve elementary ring vibrations for a six-membered ring with equal bond lengths, masses, and no substituents are illustrated with vibrational standing waves. The elementary stretching vibrations are shown in the top row and the in-plane and out-of-plane bending vibrations are shown in the second row. For rings of suitable symmetry, mixing of modes 1 and 6 results in vibrations shown in row three, which provide very strong Raman bands. The fourth row indicates the attached hydrogen motions in benzene which couple with the ring modes. Dotted lines are used to indicate nodal lines.

and 1580 cm 1. Identical para substituents provide an exception, where no quadrant stretching bands are seen in the IR spectrum since they are forbidden by symmetry. The ring semi- circle stretch has two bands in the IR near 1500 and 1450 cm 1 except in the para-substituted benzene where they are observed near 1515 and 1415 cm 1 in the IR. In mono and meta isomers, there is a very strong Raman band near 1000 cm 1. This ring vibration involves movement of the 2,4,6 carbons radially in-phase and is a result of mixing of the whole ring stretch with the sextant in-plane ring bend. In the mono- and meta- substituted benzenes, there is a strong IR band near 690 cm 1 called the sextant out-of-plane deformation or ring pucker, where the 2,4,6 and 1,3,5 sets of carbons move oppositely out-of-plane.

3.3.1. Aryl CH Wag The infrared spectrum in the region from ca. 900 to 600 cm 1 have intense bands that are highly characteristic of the number of hydrogen atoms present on the aromatic ring. The number of IR bands and their frequencies of vibrations involving the CH wag are signiﬁ- cantly determined by the number of adjacent hydrogen atoms present on the benzene ring. To a lesser extent, there is some dependence of the CH wag frequency on the electron CONJUGATED ALIPHATICS AND AROMATICS 91

TABLE 6.5 Selected IR Bands Useful for Substitution Determination of Aromatic Rings in the 950e680 cm1 Spectral Region

Substituent No. of Subst Pattern 1st CH Wag 2nd CH Wag Ring sextant out plane def

1 Mono 780e720 5 Adj CH wag NA 710e690 ring pucker

2 Ortho (1,2) 820e720 4 Adj CH wag NA inactive 2 Meta (1,3) 950e880 lone H wag 870e730 2 Adj H wag 740e690 ring pucker 2 Para (1,4) 860e790 2 Adj H wag NA inactive 3 1,2,3 805e760 3 adj H wag NA 720e680 ring pucker 3 1,2,4 900e870 lone H wag 800e760 2 Adj H wag 720e680 ring pucker 3 1,3,5 865e810 lone H wag NA 730e680 ring pucker

4 1,2,3,4 860e800 2 adj H wag NA inactive 4 1,2,3,5 850e840 lone H wag NA 720e680 ring pucker 4 1,2,4,5, 870e860 lone H wag NA inactive 6 1,2,3,4,5,6 NA NA inactive

donating or withdrawing characteristics of the substituent which effects the total electron density of the aromatic ring carbon atoms. Table 6.5 summarizes some of the more important and intense IR bands in this region. Complications in this spectral region can occur due to mechanical coupling of the CH wag with the bending vibrations of substituents such as e 1-4 NO2, carboxylic acids, and acid salts. Some of the less intense CH wag bands are not included in table 6.5 despite the fact that they are found in a relatively small frequency range. The mono-substituted vibrational mode shown in Fig. 6.15 is found at ca. 900 cm 1 and is an example of a weaker band that remains useful but is not included in Table 6.4. The range of this band is between 940 and 860 cm 1 and the frequency varies as a function of the substituent. Although this band can be used as a group frequency for structural determination, it is of greater use to demonstrate the linear frequency dependence of the band upon the calculated carbon electron density.15 The frequency of the mono-substituted benzene ring CH wag (900 cm 1) shows a well- deﬁned linear dependence on the experimentally determined Hammet values and the calculated electron density of the ring carbon atoms. The linear frequency dependence of this band upon the calculated electron density of the benzene ring para carbon atom for mono- substituted benzene ring is shown in Fig. 6.16. In many cases, the band positions for other aromatic CH wag vibrational modes listed in Table 6.5 can be estimated using an empirical expressions and a table of the mono-substituted aromatic band values (w900 cm 1 mode). Detailed examples of this type of analysis can be found in the literature (N.B. Colthup, Applied Spectrosc., 30, 589, 1976).1,4,15 Fully annotated IR and Raman spectra of selected aromatic compounds are presented in the last section for comparison and include #10e15, 27, 45, 57, 64e69, 72, and 77. 92 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

+ + - - + -

FIGURE 6.15 Approximate vibrational mode of the 900 cm 1 band CH wag for a mono-substituted benzene ring. The solid circle represents the substituent.

6.04

6.03 –OCH3

O= –NMe –OH 2 –NH–C–CH 6.02 3 –NH2 –F –C(CH3)3 6.01 –CH OH –CH3 2 6.00 + –NH3 –CCH –CN

–C=CH2

5.99 = O

O= –C–NH2 –C–OCH3

5.98 = O –C–H –NO2

O= 5.97 Mono-substituted aryl CH wag O= –C–CH3

Calculated electron density (para carbon atom) & –CF3 –C–Cl 5.96 860 870 880 890 900 910 920 930 940 Wavenumber (cm–1)

FIGURE 6.16 Correlation of the benzene ring para carbon electron density as a function of substituent with the w 1 ( 900 cm mode) CH2 wag frequency. Data adapted from N.B. Colthup, Appl. Spectrosc., 30, 589, 1976.

3.4. Fused Ring Aromatics

Polynuclear fused ring aromatics such as naphthalenes, anthracenes, and phenanthrenes have characteristic IR and Raman bands in the same general regions as benzene derivatives.1-4 The aryl-CH wag vibrations of these polynuclear aromatic compounds provide strong IR bands that provide important substitution information. Characteristic IR and Raman bands involving ring stretching vibrations are typically observed in the 1630e1500 cm 1 region. In general, alkyl-substituted naphthalenes have a doublet near 1600 cm 1, and additional bands in the 1520e1505 cm 1 and 1400e1390 cm 1. In the Raman spectra, a very strong characteristic band is observed between 1390 and 1370 cm 1 and another strong band between 1030 and 1010 cm 1. Some of the characteristic CH wag IR bands of naphthalenes are summarized in Table 6.6. CONJUGATED ALIPHATICS AND AROMATICS 93

TABLE 6.6 Selected IR bands Useful for Substitution Determination of Naphthalene Rings in the 900e700 cm1 Spectral Region

Substituent No. of Subst Pattern 1st (cmL1) CH Wag 2nd (cmL1) CH Wag 3rd (cmL1)CHWag

1 1 (mono) 810e775 3 Adj CH wag 780e760 4 adj H wag NA

1 2 (mono) 875e823 lone H wag 825e800 2 adj H wag 760e735 4 adj H wag 2 1,2 (di) 835e800 2 adj H wag 800e726 4 adj H wag NA

3.5. Heterocyclic Aromatic Six-Membered Ring Compounds

Six-membered heterocyclic aromatic compounds are benzene-like rings where one or more of the ring carbons are replaced with nitrogen atoms. Important examples of these compounds include pyridine which involves replacement with one nitrogen atom and triazine which involves substitution with three nitrogen atoms. Because, the six-membered heterocyclic rings typically have an aromatic double bonds in the ring analogous to benzenes, the resultant IR and Raman spectra have many of the same type of group frequencies. However, substitution of an OH or SH group in the ortho or para position relative to the ring nitrogen atom typically results in tautomerization and the formation of a C¼Oor C¼S bond, respectively.1,3,4 Such tautomerization also results in characteristic changes in the bands associated with the ring vibrations. Structural examples of these type of tautomerization is shown in Fig. 6.17 for 2-hydroxypyridine and cyanuric acid.

FIGURE 6.17 The resultant keto form resulting from tautomerization of 2-hydroxypyridine and Cyanuric Acid. The keto tautomer of 2-hydroxypyridine results in a carbonyl band between ca. 1650 and 1680 cm 1. The keto tautomer of cyanuric acid results in a carbonyl band cluster between 1700 and 1780 cm 1. 94 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

3.5.1. Pyridines The IR and Raman spectra of pyridine compounds have characteristic bands due to the CH stretch, ring stretching and deformation, and substituent informative CH wag vibrations. A fully annotated IR and Raman spectrum of pyridine (#15) is included in the last section for comparison. Analogous to benzene, the CH stretching bands of pyridine compounds is found in the 3100e3000 cm 1 region. The quadrant ring stretch vibrations typically give rise to moderate to strong IR and Raman bands in the 1620e1555 cm 1 region. The ring semi-circle stretch also results in characteristic IR and Raman bands in the 1500e1410 cm 1 region. The Raman spectra of pyridine compounds is typically dominated by a very strong band in the 1050e980 cm 1 region that involves the 2,4,6 carbon radial stretch. The quadrant ring in-plane bend also results in a moderate Raman band in the 850e750 cm 1 region which is correlated with the substituent position. Similarly, the strong adjacent CH wag observed in the IR in the 850e740 cm 1 region is correlated with the pyridine substitution. Some of the characteristic bands for pyridine compounds are listed in Tables 6.7 and 6.8.1-4 Protonation of the pyridine nitrogen to form the pyridinium salt results in multiple bands þ from the N eH stretch between 3300 and 1900 cm 1 that have moderate IR intensity but are weak in the Raman spectrum. The multiple band structure derives from Fermi resonance. Potentially useful Raman bands with variable intensities include the NH in-plane bend at ca. 1250e1240 cm 1 and the NH wag at 940e880 cm 1. The N-oxides of pyridines have a strong IR band in the 1300e1200 cm 1 region involving the NeOstretch.ThisbandismoderatetoweakintheRamanspectra.IR and Raman bands involving the NeO stretch and the ring in-plane bend occurs between 880 and 830 cm 1.

3.5.2. Triazines and Melamines The triazine ring in s-triazine, alkyl- and aryl-substituted triazines, and melamine compounds have characteristic IR and Raman bands due to ring stretch and deformation vibrations.1-4,16,17 The quadrant ring stretching vibrations result in strong IR and moderate Raman bands in the 1600e1500 cm 1 region. The semi-circle ring stretching vibrations result in multiple strong IR and weak Raman bands in the 1450e1350 cm 1 region. Particularly, intense Raman bands of triazine compounds include the N-Radial in-phase stretch in the 1000e980 cm 1 region and the quadrant in-plane bend in the 690e660 cm 1 region. Lastly, in the IR there is a moderately intense band in the 860e775 cm 1 region that involves the ring sextant out-of-plane deformation. Melamine consists of a triazine ring with substitution of an amino group on all three ring carbon atoms. The amino group has multiple IR and Raman bands between 3500 1 1 and 3100 cm involving the NH2 stretchandadoubletbetween1650and1620cm from the NH2 deformation. The added complexity is due to differences in hydrogen bonding in the solid crystalline state. Measurements of melamine in DMSO solution results in the expected doublet from the NH2 out-of-phase and in-phase stretch. The triazine ring itself exhibits the expected IR and Raman bands at 1550 cm 1 deriving from the quadrant ring stretch and 1470e1430 cm 1 from the semi-circle ring stretch. The unique characteristic of Raman bands include the strong band at 984 cm 1 from CONJUGATED ALIPHATICS AND AROMATICS 95

TABLE 6.7 Selected In-plane Stretching and Bending Vibrations for Pyridine and Mono-Subsituted Pyridine

Intensities1 Pyridine Assignment Region (cmL1) IR R

Pyridine Aryl CH str. 3100e3000 m m Quadrant str. 1615e1570 s m Semi-circle str 1490e1440 s mw 2,4,6 carbon radial str. 1035e1025 m vs Ring breath/str. 995e985 m s

Quadrant in-plane bend 660e600 e m 2-Mono- substituted Quadrant str. 1620e1570 s m Quadrant str. 1580e1560 s m Semi-circle str. 1480e1450 s m Semi-circle str. 1440e1415 s w CH in-plane rk 1050e1040 m s

2,4,6 carbon radial str. 1000e985 m vs Quadrant in-plane bend 850e800 w ms 3-Mono- substituted Quadrant str. 1595e1570 m ms Quadrant str. 1585e1560 s m Semi-circle str. 1480e1465 s m Semi-circle str. 1430e1410 s w

2,4,6 carbon radial str. 1030e1010 m vs Quadrant in-plane bend 805e750 w m 4-Mono- substituted Quadrant str. 1605e1565 m ms Quadrant str. 1570e1555 m m Semi-circle str. 1500e1480 m m Semi-circle str. 1420e1410 s w

2,4,6 carbon radial str. 1000e985 m vs Quadrant in-plane bend 805e785 w ms

1s ¼ strong, m ¼ medium, w ¼ weak, v ¼ very, var. ¼ variable, e ¼ zero

the N-Radial in-phase stretch and the quadrant in-plane ring bend at 675 cm 1.A sharp, moderate IR band is observed between 825 and 800 cm 1 which involves the traizine ring sextant out-of-plane deformation. This vibration involves an out-of-plane movement of all three carbon atoms and the three nitrogen atoms in opposite directions. 96 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

TABLE 6.8 Selected Out-of-plane CH wag and Out-of-plane Sextant Deformation Vibrations for Pyridine and Mono-Subsituted Pyridine

Intensities1 Pyridine Assignment Region (cmL1) IR R

Pyridine 5 adjacent H wag 760e74 s e

out-of-plane sextant def. 710e700 s e 2-Mono- substituted 4 adjacent H wag 780e740 s e 3-Mono- substituted 3 adjacent H wag 820e770 s e out-of-plane sextant def 730e690 m-s w 4-Mono- substituted 2 adjacent H wag 850e790 s e

1s ¼ strong, m ¼ medium, w ¼ weak, v ¼ very, var. ¼ variable, e ¼ zero

Tautomerizing the triazine ring by making one of the double bonds external to the ring results in the iso form in which there are fewer than three double bonds in the ring. As discussed above, substitution of the carbon atom with an OH or SH results in formation of the iso form of the triazine ring. In addition to the formation of aC¼OorC¼S bond, the IR active band that derives from the sextant out-of-plane bend will be found in the 795e750 cm 1 region. Thus, the sextant out-of-plane bend vibration found near 800 cm 1 can be used to discriminate between normal triazine rings and the iso form of the triazine ring. A fully annotated IR and Raman spectrum of ammeline (#34) and trimethyl isocyanurate (#35) are included in the last section for comparison.

3.5.3. Fiveemembered Ring Heterocyclic Compounds Pyrroles, furans, and thiophenes are five-membered ring aromatics containing two conjugated double bonds and a single nitrogen, oxygen or sulfur atom in the ring respectively. Additional compounds exist in which an additional carbon atom (position 2 or 3) are replaced with nitrogen or oxygen atoms. The double bonds are somewhat delocalized in these five-membered rings and the ring vibrations can be described using a standing wave description. Figure 6.18 depicts selected approximate ring vibrations for a five-membered ring containing one heteroatom.1 However, the ring carbon atoms are not identical and changing the substituent can significantly affect the IR and Raman spectra. Table 6.9 lists some of the characteristic ring stretching vibrations for pyrroles, furans, and thiophene compounds.1-4,18 The quadrant and semi-circle ring stretching vibrations typically mix with the CH rock vibrations. The quadrant stretching vibration consists primarily of the C¼C stretch while the first semi-circle stretch consists mainly of the CeXeC in-phase stretch with some CeC contraction. The second semi-circle stretch consists mainly of the CeXeC out-of-phase stretch. Important five-membered ring heteroaromatic vibrations not depicted in Fig. 6.18 include the ring CH stretch, the eCH¼CHe ring double bond cis CH wag and NH stretch in pyrrole type compounds. The NH stretch of pyrroles are typically observed between 3450 and CONJUGATED ALIPHATICS AND AROMATICS 97

Contr Str Str Contr Contr

Str Str Contr Str

In Out

Str

In Str Contr Out

Out Down Up Up – + + + Down In In Down + – – –

Up Down + Out Up

FIGURE 6.18 Approximate ring vibrations for a ﬁve-membered ring containing one heteroatom (solid circle) and two double bonds. The quadrant stretch predominantly involves the double bond stretching vibration.

TABLE 6.9 Selected In-plane Stretching Vibrations for Selected Pyrroles, Furans and Thiophenes

Intensities1 Pyridine Assignment Region (cmL1) IR R

Pyrrole NH str. 3500e3000 s mew ¼CH str. 3135, 3103 m s Quadrant str. þ CH rk 1530 s e Quadrant str. þ CH rk 1468 m s Semi-circle str þ CH rk 1418 m e

Semi-circle str. þ CH rk 1380 s m Ring in-phase str. 1143 m vs 1-subst pyrrole Quadrant str. 1560e1540 wemm Quadrant str. 1510e1490 m vs Semi-circle str. 1390e1380 sems

(Continued) 98 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

TABLE 6.9 Selected In-plane Stretching Vibrations for Selected Pyrroles, Furans and Thiophenesdcont’d

Intensities1 Pyridine Assignment Region (cmL1) IR R

2-subst pyrrole Quadrant str. 1570e1545 wemm Quadrant str. 1475e1460 m vs Semi-circle str. 1420e1400 sems 3-subst pyrrole Quadrant str. 1570e1560 wemm

Quadrant str. 1490e1480 m vs Semi-circle str. 1430e1420 sems Furan ¼CH str. 3156, 3121, 3092 m sem Quadrant str. þ CH rk 1590 s w Quadrant str. þ CH rk 1483 s vs Semi-circle str þ CH rk 1378 s s

Ring in-phase str. 1138 e vs 2-subst furan Quadrant str. 1560e1540 wemm Quadrant str. 1510e1490 m vs Semi-circle str. 1390e1380 sems Thiophene ¼CH str. 3110, 2998 m sem

Quadrant str. þ CH rk 1588 s e Quadrant str. þ CH rk 1408 s vs Semi-circle str þ CH rk 1357 s s Ring in-phase str. 1031 e vs Quad bend 832 s vs 2-subst thiophene Quadrant str. 1540e1514 wemm

Quadrant str. 1455e1430 m vs Semi-circle str. 1361e1345 sems

3200 cm 1. However, for ﬁve-membered rings with more than one nitrogen atom in the ring such as imidazoles, a strongly hydrogen-bonded NHeN ¼ complex occurs resulting in a broad complex set of bands in the 3000e2600 cm 1 observed in both the IR and Raman spectra. Pyrroles and furans which have nitrogen or oxygen atom in the ring, respectively, have moderate to strong IR and Raman bands involving the ¼CH stretch between 3180 and 3090 cm 1. In the case of thiophenes which has a sulfur atom in the ring, the ¼CH stretching vibration is somewhat lower in frequency at 3120e3060 cm 1. In general, the ¼CH stretching vibrations of ﬁve-membered ring heterocycles are slightly higher than CARBONYL GROUPS 99 observed for their six-membered ring analogues. Five-membered ring heterocyclic compounds with a unsubstituted eCH ¼CHe group are characterized by a strong IR band in the 800e700 cm 1 region which derives from the in-phase cis CH wag.

4. CARBONYL GROUPS

The generalized IR and Raman spectra of the carbonyl region are shown in Fig. 6.19 and the carbonyl group frequencies are summarized in Table 6.10.1-4 The C¼Ostretching vibration responsible for these bands typically give rise to strong IR bands and weak Raman bands. In addition to the carbonyl band itself, much useful information can be obtained from the bands of the attached groups. The column of spectra on the left side showsexamplesofunconjugatedcarbonyl species including ketones (near 1715 cm 1), aldehydes (near 1730 cm 1), esters (near 1740 cm 1), and acid chlorides (near 1800 cm 1). The central column of spectra shows examples of carboxylic acid, carboxylic acid salt, anhydride, and cyclic anhydride while the third column of spectra shows examples of various amides.

4.1. Review of Selected Carbonyl Species

Carboxylic acid dimers are characterized by an IR band near 1700 cm 1, and a Raman band near 1660 cm 1 which derive from the out-of-phase and the in-phase C¼Ostretchin the dimer, respectively. Weak, characteristic bands from the CeOH bend are also observed

FIGURE 6.19 The generalized IR and Raman spectra of selected carbonyl compounds between 1900 and 1400 cm 1. 100 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

TABLE 6.10 Selected Group Frequencies: Carbonyls

Intensities1 Group Assignment Frequency (cmL1) IR R

C¼O ReCOeHC¼O str. 1740e1720 s m conj-COeHC¼O str. 1710e1685 s w ReCOeRC¼O str. 1725e1705 s m conj-COeRC¼O str. 1700e1670 s m conj-CO-conj C ¼O str. 1680e1640 s m

HeCOeOeRC¼O str. 1725e1720 s m ReCOeOeRC¼O str. 1750e1735 s m Conj-COeOeRC¼O str. 1735e1715 s m g lactones C ¼O str. 1795e1760 s m ReCOeOH dimer C ¼O o.ph. str. 1720e1680 s e ”C¼O i.ph. str. 1670e1630 e m

ReCOeNC¼O str. 1695e1630 s m ReCOeCl C ¼O str. 1810e1775 s m ReCOeOeCOeRC¼O i.ph. str. 1825e1815 s m ”C¼O o.ph. str. 1755e1745 ms m Cyclic anhydride C ¼O i.ph. str. 1870e1845 m s ”” C¼O o.ph. str. 1800e1775 s mw e e R CO2 CO2 o.ph. str. 1650 1540 s w e ”CO2 i.ph. str. 1450 1360 ms s

1s ¼ strong, m ¼ medium, w ¼ weak, v ¼ very, br ¼ broad, var. ¼ variable, e ¼ zero

near 1420 cm 1. Carboxylic acid salts give rise to two bands involving the out-of-phase and in-phase CO2 stretching vibrations. The out-of-phase stretch band is observed near 1570 cm 1 and is typically quite strong in the IR but weak in Raman spectrum. The in- phase stretch band is observed near 1415 cm 1 and is typically strongest in the Raman spectrum. Anhydrides are characterized by two bands which involve the stretching of both C¼O groups in- and out-of-phase with respect to each other. Unconjugated, non-cyclic anhydrides result in bands near 1820 cm 1 and 1750 cm 1, where the higher frequency, C¼O in-phase stretch is more intense than the out-of-phase stretch for both the IR and the Raman spectra. Five-membered ring cyclic anhydrides give rise to bands near 1850 cm 1 and 1780 cm 1, where the lower frequency out-of-phase stretch band is strongest in the IR spectrum, while the higher frequency in-phase band is strongest in the Raman spectrum. CARBONYL GROUPS 101

This signiﬁcant difference between the IR intensity of the in-phase and out-of-phase C¼O stretch for the non-cyclic anhydrides and the cyclic anhydrides is directly related to the relative orientation of the two carbonyl groups. An integrated IR absorbance ratio of the two carbonyl bands can be used to predict the dihedral angle of the CeO bonds.1 Amides are characterized by strong IR bands from the C¼O stretch near 1670 cm 1. The Raman bands for the amide carbonyl stretch are typically quite weak. The primary amide ¼ e 1 group (O C NH2) also has bands near 1610 cm involving the NH2 bend as well as near 1410 cm 1 involving the CeN stretch. The non-cyclic secondary amide group (O¼CeNHeC) not only has a C¼O stretch at 1670 cm 1, but another strong band in the IR spectrum near 1550 cm 1 involving the CNH bend and the CeN stretch. In contrast, the cyclic secondary amide (O¼CeNHeC) group does not have a 1550 cm 1 band. Amides with no NH have only the C¼O stretch in this region. Fully annotated IR and Raman spectra of selected carbonyl compounds are included in Chapter 8 for comparison (see #16e29 for ketones, esters and anhydrides, 30e39 for amides, ureas, and related compounds).

4.2. Factors that Effect Carbonyl Frequencies

The carbonyl stretching frequencies are dependent upon mass, mechanical, and force constant effects. The mass effect is typically the least important factor in understanding carbonyl frequency dependence upon structure. This arises because the carbonyl stretching vibration involves mostly a change in the C¼O bond length with only a slight movement of the attached atoms (bending). This is an excellent example of a high frequency C¼O oscillator attached to a low frequency CeX oscillator (see unequal oscillators discussed earlier). The effect of changing mass on the carbonyl frequency when replacing a carbon atom with a heavier atom is quite slight due to the mass effect alone. The mass effect is more important when decreasing the substituent mass from carbon (12) to hydrogen (1) and should decrease the C¼O frequency about 17 cm 1 when comparing a ketone to an aldehyde. However, even in this simple example, the higher C¼O frequency of the aldehyde is counter to that expected by the mass effect, and demonstrates the importance of changes in the force constants.

O O C C CH2 CH2 CH2 H

The above shows the approximate carbonyl stretching vibration for a ketone and an aldehyde. The very slight movements of the carbon atoms which results in changes in the carbonyl carbon bond angle are not shown. The aldehyde CH bend and C¼O stretch are similar in energy and therefore couple more strongly than either the CeC stretch or the CeC bend. The characteristic frequencies found in strained ring carbonyls is an excellent example of the importance of mechanical effects in carbonyl compounds and is analogous to that observed in cyclic oleﬁn structures. Once again, the bond angle is the critical variable in 102 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES determining the carbonyl stretching frequency. Shown below are the structures, important bond angles, as well as the observed and calculated frequencies based upon a simple mechanical model for the carbonyl stretching frequencies of four cyclic carbonyl compounds. O O O O 120° 126° C C 135° C 150° C

Calc (cm–1) 1714 1737 1774 1836 Obs (cm–1) 1715 1740 1782 1822

The cyclic C¼O stretching frequencies as a function of the CeC¼O bond angles is shown above. The same mechanical triatomic model is used for the above calculations as was used for the cyclic oleﬁn structures earlier, where FCeC and FC¼O are 4.5 and 11.1 mdynes/A, respectively. The good agreement between the calculated and observed frequencies indicates that most of the shifts derive from mechanical effects and not from changes in force constants. Force constant effects on carbonyl stretching frequencies include mesomeric, inductive, and ﬁeld effects.1-4 Carbonyl inductive effects derive from the polar nature of the carbonyl C¼O bond. As shown below, the more the oxygen atom can attract electrons, the weaker the carbonyl C¼O force constant becomes.

O O C C

O O O RRC RClC ClC Cl 1715 cm–1 1800 cm–1 1828 cm–1

The polarity of the carbonyl bond is a consequence of the greater electronegativity of the oxygen relative to the carbon atom. Electronegative substituents on the carbon atom will compete with the oxygen for electrons and thereby raise the carbonyl frequency. Substi- tution with strongly electron-withdrawing chlorine atoms provides a classic example of this. Field effects are another example of inductive effects in the carbonyl group. In this case, the presence of an electron rich chlorine spatially near to the oxygen atom favors the non-polar C¼O group and raises the frequency. Thus, IR can discriminate between the cis and gauche rotational isomers in a-chlorocarbonyl compounds e ¼ e (CleCH2 C( O) X). Mesomeric and conjugation effects can be understood by examining resonance structures. Mesomeric effects derive from substituting the carbonyl group with lone pair electron containing heteroatoms such as chlorine, oxygen, or nitrogen. CeO AND CeN STRETCHES 103

O O –1 C Cl C Cl 1800 cm

O O –1 C OCH2 COCH2 1740 cm

O O 1660 cm–1 CNH2 CNH2

As shown above, the non-bonding electrons rearrange, resulting in donation of electrons to the oxygen atom and thereby weakening the carbonyl C¼O bond. The mesomeric effect is not important for acid chlorides since the resonance structure placing a positive charge on the chlorine atom is not favored. Conversely, the mesomeric effect is the dominant determinant of the carbonyl frequency in amides. Conjugation of a carbonyl with either a vinyl or a phenyl group typically lowers the carbonyl frequency by 20e30 cm 1. This is also a result of electron rearrangement, analogous to the mesomeric effect discussed above and can easily be understood by use of resonance structures. Shown below are the approximate frequencies for an unconjugated ketone, single, and double conjugated ketone.

O O O

CH2 C CH2 CH2 C CH CH2 CH2 CH C CH CH2

1715 cm–1 1685 cm–1 1655 cm–1

Lastly, interaction effects are key in understanding the source of two bands in anhydrides and carboxylic acid salts; these have their origin in both mechanical interactions and electron redistribution. Anhydrides have two carbonyl groups that vibrate in- and out-of-phase to each other resulting in two bands in the IR and Raman spectra. Comparison of the generalized IR spectra of cyclic and non-cyclic anhydrides shows that the relative intensity easily enables rapid identiﬁcation. Similarly, carboxylic acid salt have two bond-and-a-half CeO bonds which vibrate in- and out-of-phase to give two bands (see Fig. 6.19). The different relative intensities for these two vibrations derive from the total dipole moment change. The electron redistribution that occurs during the in- and out-of-phase vibrations for these compounds is termed as an interaction force constant and also contributes to the observed frequencies.

5. CeO AND CeN STRETCHES

The IR and Raman spectra in Fig. 6.20 illustrate some group frequencies for vibrations involving CeOorCeN stretches interacting with connected CeC vibrations.1-4 Table 6.11 104 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

FIGURE 6.20 The generalized IR and Raman spectra of selected CeO and CeN stretching bands.

TABLE 6.11 Selected Group Frequencies: Alcohols and Ethers

Intensities1 Group Assignment Frequency (cmL1) IR R

.. OH ReOH O OH str. 3400e3200 sbr vw O¼CeOH dimer OH str. 3200e2600 sbr e ” OH wag 960e875 m e .. PeOH O OH str. 2800e2100 s br vw .. SeOH O OH str. 3100e2200 sbr vw CeO e e e CH2 O CH2 COC o.ph. str 1270 1060 s w “ COC i.ph. str. 1140e800 m s ¼ e e e C C O CH2 COC o.ph. str. 1225 1200 s w e e e e Ar O CH2 Ar O str. 1310 1210 s m e e ”OCH2 str. 1050 1010 m m e e e CH2 OH C O str. 1090 1000 s mw “CeO str. 900e800 mw s N¼O AND OTHER NITROGEN CONTAINING COMPOUNDS 105

TABLE 6.11 Selected Group Frequencies: Alcohols and Ethersdcont’d

Intensities1 Group Assignment Frequency (cmL1) IR R

e e e R2CH OH C O str. 1150 1075 m mw “CeO str. 900e800 mw s e e e R3C OH C O str. 1210 1100 s mw “CeO str. 800e750 mw s

AreOH CeO str. 1260e1180 s w O¼CeOeCCeO str. 1300e1140 s w O¼CeOH CeO str. 1300e1200 s w Epoxy ring i.ph. str. 1270e1245 m s ” ring o.ph. str. 935e880 s m ” ring o.ph. str. 880e830 s m

1s ¼ strong, m¼ medium, w ¼ weak, v ¼ very, br ¼ broad, var. ¼ variable, e ¼ zero summarizes some of the important group frequencies for alcohols and ethers. Typically, vibrations involving these groups tend to give band clusters rather than single bands. The bands involving the CeO and CeN stretches of alcohols and amines show a systematic frequency dependence on their substitution (i.e., primary, secondary.). Primary alcohols and amines have bands at approximately 1050 cm 1 and near 1075 cm 1 respectively. Secondary alcohols have bands at roughly 1100 cm 1, while aliphatic secondary amines have IR bands near 1135 cm 1. Tertiary alcohols usually have IR bands near 1200 cm 1. Aliphatic ethers have characteristic IR bands near 1120 cm 1 while alkylearyl ethers have two sets of bands near 1250 cm 1 involving aryl-O stretch and 1040 cm 1 involving the e 1 O CH2 stretch. Phenols have IR bands near 1240 cm and aromatic-NH2 aniline species have IR bands roughly at 1280 cm 1 involving aryl-O and aryl-N stretches, respectively. Fully annotated IR and Raman spectra of selected alcohol and ethers are included in Chapter 8 (alcohols #40e47 and ethers 48e50) for comparison.

6. N[O AND OTHER NITROGEN CONTAINING COMPOUNDS

The generalized IR and Raman spectra illustrating group frequencies for some N¼O type compounds are shown in Fig. 6.21.1-4 Table 6.12 summarizes the selected group frequencies for selected nitrogen containing compounds. As shown in Fig. 6.21 and in Table 6.12,NOx containing compounds provide strong IR and Raman strong bands that have excellent group frequencies. e The unconjugated nitro group (C NO2) are illustrated in the top spectra in Fig. 6.21 and 1 w 1 have NO2 stretching bands near 1560 and 1375 cm . The out-of-phase stretch at 1560 cm 106 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

FIGURE 6.21 The generalized IR and Raman spectra of important bands for nitroalkanes, organic nitrates, and organic nitrites.

TABLE 6.12 Selected Group Frequencies: Nitrogen Compounds

Intensities1 Group Assignment Frequency (cmL1) IR R

e e CH2 NH2 NH2 o.ph. str. 3500 3300 m vw e “NH2 i.ph. str. 3400 3200 m m e “NH2 bend 1630 1590 m vw e “NH2 wag 900 600 sbr w e e e CH2 NH CH2 NH str. 3450 3250 vw w “CeNeC o.ph. str. 1150e1125 m mw e e e Ar NH2 C N str. 1380 1260 sbr m e þ .. e C NH3 X NH3 str. 3200 2700 s vw e ”NH3 o.ph. bend 1625 1560 mw vw e ”NH3 i.ph. bend 1550 1505 w vw N¼O AND OTHER NITROGEN CONTAINING COMPOUNDS 107

TABLE 6.12 Selected Group Frequencies: Nitrogen Compoundsdcont’d

Intensities1 Group Assignment Frequency (cmL1) IR R

þ.. e C2NH2 X NH2 str. 3000 2700 sbr w e ”NH2 bend 1620 1560 mw w þ.. e C3NH X NH str. 2700 2300 s w ¼ e e O C NH2 NH2 o.ph. str. 3475 3350 s w e ”NH2 i.ph. str. 3385 3180 s w e ”NH2 bend 1650 1620 ms w O ¼CeNHeC NH str. 3320e3270 ms w ” CNH str. bend 1570e1515 ms w O ¼CeNHeC cyclic NH str. 3300e3100 ms w >C ¼NC¼N str 1690e1630 mw ms

>C ¼NeOH OH str. 3300e3150 s w ”NeO str. 1000e900 s s e e CH2 NO2 NO2 o.ph. str. 1600 1530 s mw e ”NO2 i.ph. str. 1380 1310 s vs e e e Ar NO2 NO2 o.ph. str. 1555 1485 s e ”NO2 i.ph. str. 1357 1318 s vs e e e C O NO2 NO2 o.ph. str. 1640 1620 s mw e ”NO2 i. ph. str. 1285 1220 s s ”NeO str. 870e840 s s CeOeN ¼O s-trans N ¼O str. 1681e1640 s s ” s-cis N ¼O str. 1625e1600 s s

1s ¼ strong, m ¼ medium, w ¼ weak, v ¼ very, br ¼ broad, var. ¼ variable, e ¼ zero

is more intense in the IR spectrum while the in-phase stretch at w1375 cm 1 is more intense in the Raman spectrum. In nitroalkanes, the CeN stretch gives rise to bands in the 915e 865 cm 1 region that are intense in the Raman and mediumeweak in the IR spectra. These e e bands are sensitive to the rotational isomer present in the CH2 CH2 NO2 group. When e e w 1 the C C group is trans to the CNO2 species the C N band is at 900 cm and when the gauche orientation is present, it is at w 880 cm 1. e e The covalent nitrate group (R O NO2 ) shown in the middle spectra in Fig. 6.21 has 1 bands near 1620 and 1275 cm involving the NO2 stretch. The out-of-phase stretch at w1620 cm 1 is more intense in the IR spectrum while the in-phase stretch at w1275 cm 1 is more intense in the Raman spectrum. The NeO stretch also gives rise to a prominent band near 870 cm 1. 108 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

The covalent nitrite group (ReOeN¼O) is characterized by N¼O stretching bands between 1600 and 1640 cm 1 and a NeO stretch near 800 cm 1.TheN¼O bands are sensitive to the e e ¼ rotation isomer present in the CH2 O NO group. The N O stretch bands are typically observed near 1640 and 1600 cm 1 for the s-trans and s-cis isomers, respectively. Here s-cis indicates the single (OeC) bond is cis to the N¼Obondands-trans indicates the single (OeC) bond is trans to the N¼O bond. The fully annotated IR and Raman spectra of selected nitrogen containing compounds including amines (#51e56), C¼Ntypegroups(#57e59), N¼O type groups (60e62), and an azo group (63) are found in Chapter 8 for comparison.

7. C-HALOGEN AND CeS CONTAINING COMPOUNDS

The generalized IR and Raman spectra illustrating group frequencies for the stretching vibrations of CeCl, CeBr, CeSeC, and CeSeSeC groups is shown in Fig. 6.22.1-4 Table 6.13 shows some selected group frequencies of halogenated compounds. All of these have rotational isomers where the atom that is trans to the halogen or sulfur is either

FIGURE 6.22 The generalized IR and Raman spectra for selected vibrations involving the CeCl, CeBr, CeSeC, and CeSeSeC groups. C-HALOGEN AND CeS CONTAINING COMPOUNDS 109

TABLE 6.13 Selected Group Frequencies: Halogen Compounds

Intensities1 Group Assignment Frequency (cmL1) IR R

e CF2 and CF3 CF str. 1350 1120 vs mw AreF CF str. 1270e1100 s m CeCl CeCl str. 830e560 s s e e e e e C CH2 CH2 Cl trans C Cl str. 730 720 s s “ gauche CeCl str. 660e650 s s e e CH2 Cl CH2 wag 1300 1240 s s CeBr CeBr str. 700e515 s vs e e e e e C CH2 CH2 Br trans C Br str. 650 640 s vs “ gauche CeBr str. 565e560 s vs e e CH2 Br CH2 wag 1250 1220 s m

1s ¼ strong, m ¼ medium, w ¼ weak, v ¼ very, br ¼ broad, var. ¼ variable, e ¼ zero. a carbon or a hydrogen atom. Both the IR and Raman spectra have isolated bands CeS and C-Halogen stretching bands which are due to the rotational isomers. For chlorinated e e e e aliphatics such as C CH2 CH2 Cl, the bands involving the C Cl stretch appear near 1 e e e e e 730 and 660 cm . The aliphatic sulfide group ( CH2 CH2 S CH2 CH2) is quite similar with CeS stretching bands near 720 and 640 cm 1. For brominated aliphatics such as e e e e C CH2 CH2 Br, the bands involving the C Br stretch appear at much lower frequency near 635 and 560 cm 1. The CeF stretch of organic fluorine compounds results in strong IR bands but weak to moderately intense Raman bands. Monofluorinated compounds have a strong IR and a weak to moderate Raman band between 1100 and 1000 cm 1. Difluorinated compounds e e 1 ( CF 2) have two very strong IR bands between 1250 and 1050 cm involving the CF2 out-of-phase stretch. These bands are weak to moderate in the Raman spectrum. Trifluori- e 1 nated compounds ( CF3) have multiple strong bands between 1350 and 1050 cm involving the CF3 out-of-phase stretch. Both the IR and Raman have some characteristic bands such as the CH2 wags and the disulfide SeS stretch, which are not sensitive to rotational isomers. The disulfide group (ReSeSeR) is characterized by a very strong Raman band near 500 cm 1 that involves the e e 1 S S stretch. In addition, the CH2 Cl group has a CH2 wag band cluster near 1285 cm , e e 1 whereas the CH2 Br and CH2 S groups have these bands near 1240 cm . In aryl-halides, the CeX stretching vibration couples with the aryl ring vibrations resulting in strong IR and moderate Raman bands. Fluorine-substituted aromatics (ArdF) have a moderately strong IR band between 1270 and 1100 cm 1 involving the aryl ring CeF stretch. This same band is found between 1100 and 1030 cm 1 for the aryl-Cl species and between 1075 and 1025 cm 1 for aryl bromo species. These band regions can be further defined from high to lower frequency for para, meta, and ortho substitution of the Cl and 110 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

Br aryl halides. Iodobenzenes (para) have a characteristic aryl-I band between 1061 and 1057 cm 1. The fully annotated IR and Raman spectra of selected chlorine, bromine, and ﬂuorine containing compounds are included in Chapter 8 for comparison (#62e69, 99).

8. S[O, P[O, BeO/BeN AND SIeO COMPOUNDS

¼ The generalized IR and Raman spectra illustrating group frequencies for some S O, SO2, P¼O, and SieO type compounds are shown in Fig. 6.23. Table 6.14 summarizes the selected group frequencies for the chosen S¼O, P¼O, BeO, and SieO containing compounds.1-4 Compounds containing S¼O generally have strong characteristic IR and Raman bands. The characteristic IR and Raman bands of a sulfoxide (R2SO), sulfone (R2SO2), and a dialkyl e e sulfate (RO SO2 OR) are shown in the ﬁrst column of spectra in Fig. 6.23. The frequency of these bands can be correlated with the substituent electronegativity. In general, electronegative substituents tend to raise the S¼O frequency since they favor the S¼O resonance structure. As illustrated in the top left spectra, the intensity of the S¼O stretch near 1050 cm 1 is more intense in the IR than the Raman spectrum. For both sulfones and dialkyl sulfates, the SO2 group results in two bands due to the in- and out-of-phase stretches. The higher frequency out-of-phase SO2 stretch is stronger in the IR and the in-phase SO2 stretch is more intense in the Raman spectra. Table 6.14 also summarizes

FIGURE 6.23 The generalized IR and Raman spectra illustrating group frequencies for some S ¼O, P ¼O, and SieO type compounds. S¼O, P¼O, BeO/BeN AND SIeO COMPOUNDS 111

e e e e important bands for sulfonamides (R SO2 N), sulfonates (R SO2 OR), sulfonyl chlorides, e e e sulfonic acids (anhydrous: R SO2 OH), and sulfonic acid salts (R SO3 ). ¼ The characteristic IR and Raman bands of a phosphine oxide (R3P O) and phosphorus e ¼ ¼ ester ((R O)3P O) are shown in the second column of spectra in Fig. 6.23. The P O stretching frequency depicted have been shown to correlate with the sum of the substituent

TABLE 6.14 Selected Group Frequencies: Sulfur, Phosphorus, Silicon, and Boron Compounds

Intensities1 Group Assignment Frequency (cmL1) IR R

Sulfur Cpds SH SH str. 2590e2540 w s e e e C SO2 CSO2 o.ph. str. 1340 1290 s w e “SO2 i.ph. str. 1165 1120 s s e e e C SO2 NSO2 o.ph. str. 1380 1310 s m e “SO2 i.ph. str. 1180 1140 s s e e e e C SO2 O CSO2 o.ph. str. 1375 1335 s ms e “SO2 i.ph. str. 1195 1165 s s e e e C SO2 Cl SO2 o.ph. str. 1390 1361 s w e “SO2 i.ph. str. 1181 1168 s s e e e C SO2 OH anhydrous OH str. 3100 2200 sbr w e ““ SO2 o.ph. str. 1352 1342 s w e ““ SO2 i.ph. str. 1165 1150 s s e þ e e C SO3 H3O (hydrate) OH str. 2800 2100 sbr e e ““ SO3 o.ph. str. 1230 1120 s e e ““ SO3 i.ph. str. 1085 1025 m ¼ ¼ e C2S OSO str. 1065 1030 s w Phosphorus Cpds PH PH str. 2450e2270 ms mw

P ¼OP¼O str. 1320e11402 sm PeOH OH str. 2800e2100 sbr. vw e e e e e P O CH2 P O C str. 1050 970 s mw PeOeAr OeAr str. 1240e1160 s mw “PeO str. 995e855 s w Silicon Cpds SiH SieH str. 2250e2100 vs m

SieOSieO str. 1100e1000 vs w e e Si CH3 CH3 i.ph. bend 1270 1250 vs w (Continued) 112 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

TABLE 6.14 Selected Group Frequencies: Sulfur, Phosphorus, Silicon, and Boron Compoundsdcont’d

Intensities1 Group Assignment Frequency (cmL1) IR R

Boron Cpds BH BeH str 2640e2350 s mw BH (complete octet) BeH str 2400e2200 s mw BeHeB (Bridge) BeHeB str. 2220e1540 s mw BeOH OH str 3300e3200 s w

BeOBeO str 1380e1310 s var BeNBeN str. 1465e1330 s var B-Phenyl CeBeC/ring str. 1440e1430 s

1s ¼ strong, m ¼ medium, w ¼ weak, v ¼ very, br ¼ broad, var. ¼ variable, e ¼ zero 2 ¼ ¼ w 1 e ¼ w 1 Electronegative substituents raise the P O frequency (example: R3P O 1160 cm ,(R O)3P O 1270 cm ) electronegativities. In general, the IR spectrum provides a better selection of strong characteristic bands. Table 6.14 summarizes selected important group frequencies for phosphorus compounds including the PH stretch, the OH stretch of the PeOH group, and the PeOeC e e e stretch of the P O CH2 group. The P O-phenyl group gives rise to two bands involving the phenoxy CeO stretch and the PeO stretch. The characteristic IR and Raman bands of a siloxane polymer is shown in the bottom right hands corner in Fig. 6.21. In general, IR spectroscopy provides a much better selection of strong, characteristic group frequency bands of silicon compounds. For silicones, the Si- 1 e CH3 group has a good IR in-phase CH3 bending band near 1265 cm and the Si O stretch has a strong, broad IR band in the 1100e1000 cm 1 region. Table 6.14 also summarizes selected important group frequencies for boron containing compounds. The BeO stretch results in a strong characteristic IR band between 1380 and 1310 for both organic and inorganic compounds containing the BeO species. Compounds containing BeN species also result in strong characteristic IR bands between 1465 and 1330 cm 1. Little information on the characteristic Raman bands BeO and BeN containing species are available in the literature. The interpreted IR and Raman spectra for sulfur containing compounds (70e76, 83, 84), phosphorus containing compounds (77e80, 88, 89), silicon containing compounds (81, 93, 108), and boron containing compounds (64, 90) are included in Chapter 8 for comparison.

9. INORGANICS

Both IR and Raman spectroscopy provides important structural information on a multi- tude of ionic inorganic compounds.19 Both techniques are sensitive to the crystalline form of the inorganic species. Table 6.15 summarizes selected IR and Raman bands for a few common inorganic compounds. The interpreted IR and Raman spectra of several selected inorganic compounds (#82e94) are included in Chapter 8 for comparison. INORGANICS 113

TABLE 6.15 Selected Group Frequencies: Common Inorganic Compounds

Inorganics IR bands (cmL1) Raman bands (cmL1)

þ NH4 3100 s, 1410 s 3100 w, 1410 w NCO 2170 vs, 1300 m, 1210 m 2170 m, 1300 s, 1260 s NCS 2060 vs 2060 s CN 2100 m 2080 s CO3 1450 vs, 880 m, 710 w 1065 s HCO3 1650 m, 1320 vs 1270 m, 1030 s NO3 1390 vs, 830 m, 720 w 1040 s NO2 1270 vs, 820 w 1320 s

2 SO4 1130 vs, 620 m 980 s HSO4 1240 vs, 1040 m, 870 m 1040 s, 870 m SO3 980 vs 980 s

3 PO4 1030 vs, 570 m 940 s e e ( SiO2 )x 1100 vs, 470 m e TiO2 660 vs, 540 vs s ¼ strong, m ¼ medium, w ¼ weak, v ¼ very, e ¼ zero. 114 6. IR AND RAMAN SPECTRA-STRUCTURE CORRELATIONS: CHARACTERISTIC GROUP FREQUENCIES

Chapter 6: Problems 1. Explain the frequency dependence observed for CH3 in-phase bending band in the e ¼ 1 e ¼ 1 e ¼ 1 following series: B CH3 1310 cm ,C CH3 1380 cm ,N CH3 1410 cm , e ¼ 1 e ¼ 1 O CH3 1445 cm , and F CH3 1475 cm . 2. Explain the observed splitting in the CH3 in-phase bend IR band in isopropyl or gem-dimethyl groups and t-butyl groups. 3. ¼ Explain the observed frequency dependence of the C CH2 wag vibration: h e ¼ ¼ 1 h e ¼ ¼ 1 e ¼ ¼ (N C)2 C CH2 985 cm ,N C CH CH2 960 cm ,R C CH2 910 1 e e ¼ ¼ 1 cm ,R O C CH2 813 cm . Hint draw possible resonance structures and ¼ consider mesomeric electron donation to the CH2 carbon. How would you expect the IR intensity to vary? 4. Trans-substituted olefins (ReC¼CeR) show the following systematic increase in the observed CH wag. An isolated trans alkene (T) has a CH wag at 965 cm-1,a conjugated transetrans diene (TT) at 986 cm 1, the transetransetrans alkene (TTT) at 994 cm 1,andthetransetransetransetrans alkene (TTTT) at 997 cm 1. This is a result of vibrational interaction with conjugated diene groups. Using diagrams of the CH wag explain this progression. Hint: mechanical interaction (see N.B. Colthup, Appl Spectrosc., 25, 368, 1971). 5. ¼ ¼ The P O, S O, and SO2 stretching frequencies are relatively unaffected by conjugation or strained ring. How does the geometry relate to this? The inductive ¼ ¼ effect has a significant impact on the P O, S O, and SO2 stretching frequencies. ¼ 4 þe Where the inductive effect is: X3P O X3P O How could changing the substituents change the frequency (i.e., what simple parameter would explain the frequency shifts)? 6. Draw the five expected ring stretching modes for a five-membered ring. Use standing wave to help. Use your vibrations to assign IR bands observed for the following ring stretch vibrations:

Region 1 Region 2 Region 3 Rings (IR:var, R:var) (IR:m, R:vs) (IR:ms, R:s)

1-Substituted pyrrole 1560e1540 1510e1490 1390e1380 2-Substituted pyrrole 1570e1545 1475e1460 1420e1400 2-Substituted Furans 1605e1560 1515e1460 1400e1370 2-Substituted Thiophenes 1535e1514 1454e1430 1361e1347

7. The aromatic sextant stretch typically is IR and Raman forbidden and is therefore not observed. This band has been assigned for certain Cl-substituted aromatics to occur between 1330 and 1305 cm 1 which is below that observed for either the quadrant or semi-circle ring stretches. Draw the two different extremes of the sextant ring stretch. The lower frequency is due to an interaction force INORGANICS 115

constant. Explain this concept as it relates to the observation for the aromatic sextant stretch. 8. How does the interaction force constant explain the observed differences between e e e e 1 2,4-pentanedione (CH3 CO CH2 CO CH3 at 1725 and 1707 cm ) and an e e e e 1 anhydride (CH3 CO O CO CH3 at 1833 and 1764 cm ).

References

1. Colthup, N. B.; Daly, L. H.; Wiberley, S. E. Introduction to Infrared and Raman Spectroscopy, 3rd ed.; Academic: New York, NY, 1990. 2. Bellamy, L. J.; The Infrared Spectra of Complex Molecules, 3rd ed.; Chapman and Hall: New York, NY, 1975; vol. 1. 3. Lin-Vien, D.; Colthup, N. B.; Fateley, W. G.; Grasselli, J. G. Infrared and Raman Characteristic Frequencies of Organic Molecules; Academic: San Diego, 1991. 4. Socrates, G. Infrared Characteristic Group Frequencies, 2nd ed.; John Wiley: New York, NY, 1994. 5. Jordanov, B.; Tsankov, D.; Korte, E. H. J. Mol. Struct. 2003, 651e653, 101e107. 6. Atamas, N. A.; Yaremko, A. M.; Seeger, T.; Leipertz, A.; Bienko, A.; Latajka, Z.; Ratajczak, H.; Barnes, A. J. J. Mol. Struct. 2004, 708, 189e195. 7. Amorim da Costa, A. M.; Marques, M. P. M.; Batista de Carvalho, LA. E. Vib. Spectrsoc. 2002, 29,61e67. 8. Balabin, R. M. J. Phys. Chem. A 2009, 113, 1012e1019. 9. Colthup, N. B. J. Chem. Educ. 1961, 38 (8), 394e396. 10. Colthup, N. B.; Orloff, M. K. Spectrochim. Acta, Part A 1971, 27A, 1299. 11. Determined by the author using Hammet values from Domingo, L. R.; Perez, P.; Contreras, R. J. Org. Chem. 2003, 68, 6060e6062. 12. Tasumi, M.; Urano, T.; Nakata, M. J. Mol. Struct. 1986, 146, 383e396. 13. Palafox, M. A. Int. J. Quantum Chem. 2000, 77, 661e684. 14. Versanyi, G. Vibrational Spectra of Benzene Derivatives; Academic: NY, 1969. 15. Colthup, N. B. Appl. Spectrosc. 1976, 30, 589. 16. Larkin, P. J.; Makowski, M. P.; Colthup, N. B. Spectrochim. Acta A 1999, 55, 1011e1020. 17. Larkin, P. J.; Makowski, M. P.; Colthup, N. B.; Flood, L. Vibr. Spectrosc. 1998, 17,53e72. 18. El-Azhary, A. A.; Hilal, R. H. Spectrochim. Acta, Part A 1997, 53, 1365e1373. 19. Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part A: Theory and Applications in Inorganic Chemistry, Part B: Applications in Coordination, Organometallic, and Bioinorganic Chemistry, 5th ed.; John Wiley: New York, NY, 1997.

CHAPTER 7

General Outline and Strategies for IR and Raman Spectral Interpretation

Spectroscopists must develop an analytical toolbox suitable for their needs. This includes the ability to measure a suitable spectrum, understand the basic chemistry of the compound, and systematically interpret the spectrum. In this chapter, the IR and Raman spectrum will be discussed briefly in terms of spectral regions rather than functional groups. Both Raman and FT-IR spectroscopies provide important molecular structural information. However, the successful application of both techniques relies heavily on the skill of the spectroscopist. There are common skills used for solving structural problems using vibrational spectroscopy. In general, tools and skills that can be called upon include the following components: • Interpersonal and communication skillsdDefine the problem and get background information on the sample. • InstrumentationdSelect most appropriate technique and sample preparation. • Data analysis techniquesdExperience is important in selecting the most appropriate tool for your application. • Spectral interpretation skills. • Spectral database tools (spectral libraries, interpretation software). • Ab initio-based normal mode analysis (ultimate structural verification).

1. TOOLS OF THE TRADE

IR and Raman spectroscopies are used to study a very wide range of sample types and may be examined either in bulk or in microscopic amounts over a wide range of temperatures and physical states (e.g., gases, liquids, latexes, powders, ﬁlms, ﬁbers, or as a surface or embedded layer). Because IR and Raman spectroscopies have a very broad range of applications, it is important to be knowledgeable about the advantages and limitations of various available techniques in order to select the most appropriate technique for the problem facing the spectroscopist. Often a broad-based knowledge of spectroscopy is required including an understanding of the instrument, the data analysis as well as spectral interpretation skills.

117 118 7. GENERAL OUTLINE AND STRATEGIES FOR IR AND RAMAN SPECTRAL INTERPRETATION

Basic instrumental techniques for bulk analysis include mid-IR (most commonly FT-IR) as well as Raman spectroscopy. Raman spectroscopy has various laser excitation sources and instrument designs (such as FT-Raman or grating-based instruments). When examining smaller samples micro-analysis techniques must be employed such as microscopy (IR and Raman, imaging, and confocal), and micro-ATR for IR. Once a suitable sampling technique has been selected to provide the spectrum (or spectra) needed, a data analysis technique to provide information needed to solve the problem is required. For identiﬁcation and structural veriﬁcation purposes, this can include spectral databases and interpretation. Chemometric data analysis may be employed for developing quantitative models or analysis of large spectral data sets such as those encountered in imaging techniques.

100 IR 1

%T 60 723

1379 CH i. ph. CH i. ph. rk . 20 bend 1466 2859 2959 CH bend + CH C–C–C 2875

CH 2937 CH , CH str . CH o. ph. bend i. ph. o. ph. str Ra o.ph. twist 310

0.1 1451 2963 I str 902 1302 394 840 357 1081 1138 1046 776 2733

0.0 OH str 100 . IR 878 935 996 60 1298 CH chain %T 1408 1123 2638

2956 C–CC–O

C–O–H 720 1070 i. ph. rock 3303 bend o. ph. str . 1473

CH 2850 . crystal splitting

20 1463

o. ph. str . 2918 0.24 CH CH CH Trans chain 2846 o. ph. bend C–C–C i. ph str . CH —(CH ) —OH o. ph. str.str 2881 i. ph. str . 3 2 15 Ra 0.16 1296

1437 Trans chain

I 1063 1130

0.08 891 C–C–C o. ph str. . 2724 1459 1369 0.00 Dimer O…H…O 100 CH wag o. pl. wag OH str . 3 688

IR 548

60 891 CH 1099 1348 720 941 %T 1188 CH rk 1229 o. ph.str 2676 CH 1431 2955 Trans chain

C=O 1295 20 i. ph. str O 2849 CH o. ph. str . 1472 C–O str. C–C–C i. ph.str 1703 2918 in dimer 0.8 o. ph. str . CH CH CH3—(CH2)14—C—OH 2882 bend Trans chain 2846 twist Trans chain . C=O 1296

Ra CHo. ph. str 1438

2924 C–C–C o. ph. str 1063

0.4 1422 i. ph. str . 1129

I 1462 2959 1099 375 893 2725 671 1175 in dimer 1634 0.0 100 H O OH. str CH chain wag 4 IR 60 H O bend 1421 1302 CH chain 1113 720 2957

%T 3429 1622 CH i. ph. rk.rk. CH CO i. ph. str . ++ 20 o. ph. str [CH —(CH ) —CO —] Ca 1576 1542 i. ph. str . 1470 3 2 14 2 2 2850 2917 CO o. ph. str CH chain chain 0.40 CH CH CH bend i. ph. twist C–C–C i. ph.str CH chain 2846 Ra o. ph. str 2881 C–C–C o. ph. str . 1296 1441 1461 1063

I 1130 1103 891 2724 1370 1176 1569 2610 0.00 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber (cm )

FIGURE 7.1 The FT-IR and FT-Raman spectra of n-heptane, 1-hexadecanol, palmitic acid, and calcium palmitic acid salt. IR SAMPLE PREPARATION ISSUES 119

Success will often depend on your selection of the most suitable technique for the problem at hand. As a rule, mid-IR provides a better general workhorse technique than Raman spectroscopy because it contains a greater selection of bands characteristic of functional groups. This is illustrated in the Fig. 7.1 of the IR and Raman spectra for several organic species. The Raman spectra have characteristic bands for the aliphatic backbone, but do not have strong bands associated with important functional groups of the alcohol, carboxylic acid, and carboxylic acid salt. IR has strong characteristic bands for the aliphatic methyl and methylene groups as well as the alcohol, carboxylic acid, and carboxylic acid salt groups. The Raman spectrum of each of the four species is very similar with bands characteristic of the methyl, methylene, and skeletal carbon backbone. In the four compounds selected (n-heptane, 1-hexadecanol, palmitic acid, and calcium palmitic acid salt), the Raman spectrum does not provide strong bands for the hydroxyl, carbonyl, or carboxylic acid. Moderate-to-strong Raman bands can occur for carbonyl groups that are more polarizable (e.g., amide carbonyls or the very strong carbonyl observed in isocyanurate). There are functional groups for which Raman is the preferred method while some functional groups provide useful bands in both types of spectra. In general, IR provides a broader representation of characteristic bands for a greater variety of functional groups. The Raman spectra have characteristic bands for the aliphatic backbone, but do not have strong bands associated with important functional groups of the alcohol, carboxylic acid, and carboxylic acid salt.

2. IR SAMPLE PREPARATION ISSUES

The quality of the information that can be derived from a FT-IR spectrum is directly related to the quality of the spectrum itself. Therefore selection of the appropriate sample technique and the resultant spectrum quality is critical. Operators must develop requisite sample-preparation skills necessary to measure photometrically accurate spectra. In the case of neat liquids, the liquid film should be uniformly thick (ca. 5e8 mm) without holes or voids to insure a good, quantitative IR spectrum. Similarly, films (cast or pressed) should also be uniformly thick without holes or voids. Lastly, solid-powdered samples can be prepared as a uniform dispersion in either a Nujol or a KBr matrix. In both cases, the sample powder must be sufficiently grounded and mixed with the support matrix to insure a good, artifact-free IR spectrum. A wide variety of IR sample preparation techniques exist because there is not a universal sampling technique that will provide high-quality IR spectra for all samples. The nature of the particular sample will often dictate the selection of the technique. As an example, the IR spectra of potato starch measured using a Nujol mull, KBr disc, water cast film, and ATR sampling are shown in Fig. 7.2. Starch provides an excellent example of the importance of selecting an appropriate IR sample-preparation technique suitable for the sample of interest. Both the Nujol mull and KBr disc sample preparations are inappropriate for starch and result in poor-quality IR spectra. The Nujol mull provides an extremely false spectrum and results in very limited spectral information that could be used for identification and interpretation. The KBr disc 120 7. GENERAL OUTLINE AND STRATEGIES FOR IR AND RAMAN SPECTRAL INTERPRETATION

100 (a) (c)

80 2149 1642 2154

60 852 932 708 762 Transmittance 1364 2929 40 N

N 20 1645 1246 858 1152

Nujol mull 764 932 719 3382 573 1081 984 3066 1156 Water cast film/ZnSe 1457 1373 1025 100 (b) (d)

80 2085 1244 1636 1456 2928 1416 60 1337 3279 856 Transmittance 1150 928 761 40 853 1077 1645 928 1239 764 1416 1372 709 2926 20 525 KBrdisc 576 ATR 1159 995 1082 3433 1019

3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 Wavenumber Wavenumber

FIGURE 7.2 IR Spectra of potato starch: Comparison of (a) Nujol mull (N ¼ Nujol signal), (b) KBr disc, (c) water cast film on ZnSe sample preparation, and (d) ATR sampling. spectrum, while false, is a significant improvement over the Nujol mull preparation and could be used for identification. Dissolving the starch in water and preparing a cast film on ZnSe results in a photometrically accurate IR spectrum. The resultant IR spectrum is of an amorphous film. Lastly, using ATR, an excellent IR spectrum is obtained of the starch powder. Note that the ATR technique results in changes in peak position, shape, and also results, as is typical of ATR, in a wavelength dependence of the band intensities. Five different general criteria should be kept in mind for suitable IR sample preparation for both samples and library reference spectrum. 1. Suitable band intensities in the spectrum. The strongest band in the spectrum should have intensity in the range of 5e15% transmittance. The resulting preparation must be uniformly thick and homogenously mixed without holes or voids to insure a good quality spectrum. 2. Baseline. The baseline should relatively be flat. The highest point in the spectrum should lie between 95 and 100% transmittance. 3. Atmospheric compensation. Water vapor and carbon dioxide bands should be minimized. Since the sample scan is ratioed against a previously measured background, spectral subtraction of water vapor/carbon dioxide, reference spectrum should be used. OVERVIEW OF SPECTRAL INTERPRETATION 121

4. Spurious bands. Any band that does not belong to the sample is spurious and must be accounted for or better yet eliminated. Use of an IR window contaminated with a previous sample is a very common source of spurious bands. 5. X-axis scale. Plots should employ a 2X-axis expansion and not a simple linear X-axis. This provides an expansion of the important ﬁngerprint region. Some spectral databases such as the Aldrich collection utilize a 4X-axis expansion.

2.1. Select Suitable Sampling and Know the Limitations

The sample and problem at hand will determine if a bulk or microscopy measurement is used. The sampling by Raman spectroscopy is straightforward with fluorescence interference representing the main limitation. In the case of IR spectroscopy, sample preparation choices must be made to produce the most photometrically accurate spectrum. Sample preparation for bulk analysis includes KBr disc, Nujol mull, ATR, DRIFTS, and cast films. For a KBr disc preparation, the entire spectrum is available, but KBr is hydroscopic. Water will be introduced in the KBr disc preparation and this will affect the ability to interpret the OH/NH stretching region. For a Nujol mull sample preparation, there will be interferences from the mulling oil aliphatic groups. ATR can be considered a more universal sampling choice but the IR band intensities exhibit a wavelength dependence. Some band shape distortions will occur. Less commonly used techniques include DRIFTS where the analyst must be concerned about the photometric accuracy of the spectrum. Lastly, a solvent cast films can be used. Issues with this technique include preparing a uniform film, eliminating much or all of the solvent, and the resultant crystalline state of the material.

3. OVERVIEW OF SPECTRAL INTERPRETATION

Spectral interpretation requires a systematic, knowledge-based approach for optimal success. Both the sample IR and Raman spectrum and any reference spectrum must be of good quality. Before beginning to interpret the IR and Raman spectrum, the analyst should get a suitable amount of background information. Spectral interpretation is a critical skill that is learned with practice and experience. Resources to use include electronic and paper libraries, empirical characteristic frequencies for chemical functional groups as well as outside vendor and interior libraries. The quality of the available reference library is critical. The IR and Raman libraries ideally should capture knowledge of the spectroscopy of the band assignments of molecules included in the database in order to facilitate interpretation of other molecules.

3.1. Hierarchy of Quality for Spectral Reference Libraries

Spectral reference libraries have a hierarchy of quality. The usefulness of a spectral library is deﬁned in part by how accurate it is and how much known information is captured in it. For example, the resolution of both the sample and reference libraries should match. In the case of IR spectrum, the sample preparation should always be indicated. In the case of Raman spectral reference libraries, a non-resonant excitation frequency should be employed and the ﬁnal processed spectrum should include a background intensity correction. 122 7. GENERAL OUTLINE AND STRATEGIES FOR IR AND RAMAN SPECTRAL INTERPRETATION

The following is a general hierarchy of spectral library quality: • Spectrum incorrectly identiﬁed with wrong structure. (This is the worst case scenario.) An example of this can include an IR spectrum dominated by water vapor and carbon dioxide. • A false IR spectrum with trade name only (useless). • A photometrically accurate IR or Raman spectrum with trade name only (almost useless). • A photometrically accurate IR or Raman spectrum with structure (Best case scenario of commercial libraries). • A fully interpreted photometrically accurate IR and Raman spectrum with structure (Best case scenario of in-house libraries).

3.2. Computer-Based Libraries and Software Tools

Computer-based systems that provide guidance in spectral identification or group frequency analyses are a useful tool, but have limitations that must be understood. The usefulness of a spectral library is defined in part by how accurate it is and how much known information is captured in it. The spectral library must contain structures similar to the unknown in order to be useful. The critical decision to be made is whether the measured spectrum can be considered consistent with the reference spectrum. A common first step for structural identification is to employ a spectral library search. A fundamental limitation is that libraries contain no knowledge of the chemistry of the system and are limited by the size and scope of spectral libraries. Libraries are most useful if the compound of interest, with suitable sample preparation/presentation, exists in the database. A reference spectrum and sample of the same species, but different crystallinity, in the library will negatively affect the accuracy of the identification. In general, a number of automatic search methodologies exist that can be used to compare the spectrum of an unknown sample against many different spectra in the library. These include a simple peak matching to discrimination analysis using Euclidean distance, wavelength correlation (or other algorithms). A search simply reports the best-known match from the spectral library. The unknown may be from an entirely different class of materials. Another approach is to use an empirically based, computer-assisted structural interpretation to aid in a group frequency analysis of the IR and Raman spectrum. The analyst should also use their background knowledge of the chemistry of the sample to help screen such results. One approach involves software that incorporates numerous correlation tables organized by functional group fragments. The analysis of spectrum results in suggested fragments with highlights of important bands for that fragment. These fragments can be combined to provide a hypothetical structure for confirmation. Some software allows the addition of functional group band assignments by the analyst. This can enable the software to focus on the type of molecules commonly encountered in the particular lab. Approximate intensities are often included and include the frequency range. This is a more flexible analysis tool than the “brute force” spectral library approach. The most rigorous approach to structural verification involves using ab initio determined structure with normal mode analysis. The calculations are based on an isolated molecule and result in the theoretical IR and Raman band frequencies, relative intensities, and corresponding vibrations. Interactions encountered in the condensed phase such as hydrogen bonding OVERVIEW OF SPECTRAL INTERPRETATION 123 and various environments from different crystalline structures are not taken into account. Therefore, the computational results are most appropriate for gas-phase spectra. The size of the molecule limits this approach because of the computationally intensive analysis employed. Analysis of the Cartesian displacement vectors describing the vibrations from the normal mode analysis can provide important insight into group frequencies and mechanical interactions of the vibrations in the molecule. This approach provides the most rigorous structural verification approach.

3.3. Deﬁne the Problem that Needs to be Solved

The first step involves defining the problem. Ideally, this should be done before the spectrum of a sample is measured. A complete unknown is rare. Get all the background chemistry information available so that you have a good sample history. Obviously, the analyst should be clear if the sample is research or product related. If this is a research sample, obtain the reaction scheme. Ask the submitter what are the expected products and impurities and if this is an intermediate or final product. If the sample is product related then the analyst should determine the product area/general area of chemistry. Exam- ples can include paper industry related, polymer additives, polymers, and pharmaceutical API’s. IR and Raman spectroscopy are commonly employed for contaminant analysis. In this case, find out what the source matrix is and if this is believed to be a contaminant. In some instances, an identification of extracted materials is needed. In this case, determine the matrix from which the material was extracted. What solvent was used? What filters were used? The analyst must know what spectral signals might be expected from these possible contaminants. Questions to be asked to the submitter can include the following: Where did the sample come from exactly? Was there any sample manipulation prior to analysis? Has there been similar work done in the past? What other techniques are being used in the analysis?

3.4. Examine the IR and Raman Spectrum

The first step of interpreting the IR and Raman spectrum is to identify any common impurities that could be present. Some common impurities include silicone oil, water, plasticizers such as phthalates, flow aids such as Mg stearate and commonly encountered polymers (e.g., PE, Nylon, Teflon), and long-chain aliphatics. Look for possible solvents that may have been introduced by any extraction procedures and not fully removed from an isolated reaction product. The analyst should also look for inorganic sulfates, sulfites, or nitrates that may be present as a result of treatment of a reaction mixture with sulfuric acid or nitric acid. Next, determine if the spectrum represents single component or multiple components. Almost all organic and many inorganic species have IR and Raman bands. A complex spectrum can represent either a complex molecule with a wide range of functional groups or multiple components. Multiple component identification is challenging and is a skill that improves with practice. If you have assigned multiple species, review if that is consistent with the chemical background. If possible estimate relative amounts of components present. 124 7. GENERAL OUTLINE AND STRATEGIES FOR IR AND RAMAN SPECTRAL INTERPRETATION

Be aware of orientation/crystallinity effects since vibrational spectroscopy has excellent environmental sensitivity. This can result in very different IR and Raman spectra for amorphous versus crystalline states. Most of the observed spectral differences are a result of changes in hydrogen-bonding environments. Because of this the analyst should try to ensure that the reference spectra followed the same sample-preparation method and has the same crystalline state as the unknown. Some sample preparations (e.g., cast films) can result in a different crystalline state from the sample of interest. The last step for structural identification and verification is to assign all main peaks in the IR and Raman spectrum. A standard systematic way to begin analyzing the IR/Raman spectrum is to begin at the high wavenumber end of the spectrum (4000 cm 1) and look for the presence and absence of characteristic absorptions as you move to lower wavenumbers. The most common and distinctive bands can then be organized into several spectral regions. Whenever possible, assignments should utilize confirming bands. If possible, measuring a full spectral region (4000e400 cm 1) is important because, for example, the confirming bands for many inorganic species occurs below 650 cm 1 (vide infra). When possible use the basic knowledge about the sample and the chemistry associated with it. Check for group frequencies associated with suspected structural components. Computer-based spectral libraries and structural interpretation software may be valuable tools. Remember to keep in mind the limitations and spectral contributions from any sample-preparation techniques used. Try to assign the most intense bands first. In most cases, you will not be able to fully and accurately assign group frequencies to all of the bands in the spectrum.

4. INTERPRETATION GUIDELINES AND MAJOR SPECTRAeSTRUCTURE CORRELATIONS

This section is to be used as a general guide to interpret IR and Raman spectra systematically. As a ﬁrst check, examine the overall spectral appearance. If the spectrum is very simple with only a few vibrational bands then focus on a low molecular weight organic or inorganic species. Look at inorganic salts such as sulfate, carbonate, or nitrate or simple common organic solvents and water. For organics and hydrocarbons look for bands in the IR and Raman spectra in the region between 3200 and 2700 cm 1, because these are excellent group frequencies associated with CeH-type stretches. After a quick evaluation of the spectral appearance and determining, if hydrocarbons are present, begin to interpret the vibrational spectrum. Start from 4000 cm 1 and work systematically to lower wavenumbers. The presence and absence of functional groups needs to be noted.

4.1. Hydroxy (OH), Amino (NH), and Acetylene (hCH) Groups: 3700e3100 cmL1

Bands in this region are typically due to various OH and NH stretching vibrations. Hydrogen bonding will have a large effect on the amino and hydroxyl stretching vibrations. The OH stretch is medium to strong in intensity in the IR spectrum but is generally weak in the Raman spectrum. IR spectroscopy will be excellent for NH stretching vibrations. Raman INTERPRETATION GUIDELINES AND MAJOR SPECTRAeSTRUCTURE CORRELATIONS 125 spectroscopy will be poor for OH and acetylene CH stretching vibrations but moderate for NH stretching vibrations. In the condensed phase, the hydroxyl OH stretching band is generally intermolecularly hydrogen bonded with a broad band appearing between 3550 and 3230 cm 1. In some cases due to crystalline structure or steric hindrance, the hydroxyl group is not hydrogen bonded and resultant sharp and moderately strong free OH stretching bands are observed between 3670 and 3580 cm 1. The OH stretches for water alcohols and phenols are generally observed at 3400 cm 1 but can be found between 3700 and 3300 cm 1. The observed OH stretch depends upon the strength of the hydrogen bond. Acidic protons for the hydroxyl species of carboxylic acid dimers and phosphoric acids result in very broad bands centered at ca. 3000 cm 1. IR bands for hydrogen-bonded amino groups are generally not as broad as those observed for hydrogen-bonded hydroxyl groups. Primary amine (NH) groups result in a single weak 1 band between 3500 and 3300 cm while a secondary amine (NH2) group results in a weak doublet between 3550 and 3250 cm 1 with a spacing of about 70 cm 1. A secondary amide 1 NH results in a stronger band between 3470 and 3200 cm while a primary amide (NH2) group results in a strong doublet between 3550 and 3150 cm 1 with a spacing of about 100e200 cm 1. The acetylene hCH group has a moderate-to-strong sharp IR band between 3340 and 3280 cm 1. The band is quite weak in the Raman spectrum. e Lastly, weak overtones from carbonyl bands can occur between 3500 and 3400 cm 1 region. Typically, the overtone band frequencies will be ca. 20 cm 1 less than twice the carbonyl stretching band wavenumber and the intensity will be signiﬁcantly less intense than the carbonyl stretching band.

4.2. Unsaturated Aryl and Oleﬁnic Groups: 3200e2980 cmL1

Both IR and Raman spectroscopy provide moderately strong bands for these groups. If sharp bands are observed between 3000 and 3200 cm 1 then it is likely an unsaturated group is present. Aromatics have multiple weak bands from CH stretch vibrations between 3100 and 3000 cm 1. Most oleﬁns have characteristic CH stretching bands in the 3100e2980 cm 1 region. Observation of isolated bands at 3010 cm 1 and 3040 cm 1 most likely indicates a simple oleﬁnic group. Pyroles and furans will typically have bands in the 3180 and 3090 cm 1 region. Three-membered rings such as cyclopropyl and epoxy rings will also have bands in 3100e2990 cm 1 and 3060e2990 cm 1 regions, respectively.

4.3. Aliphatic Groups: 3000e2700 cmL1

Well-deﬁned, strong characteristic IR and Raman bands for CeH stretching vibrations characteristic of aliphatics are typically observed. Both methyl and methylene groups (CH3,CH2) result in doublets at slightly different frequencies. Methyl CH stretching bands typically have bands between 2975e 2950 cm 1 and 2885e2865 cm 1. Methylene CH stretching bands typically have bands between 2940e2915 cm 1 and 2870e2840 cm 1. The relative intensities of the bands can be used to estimate the relative amount of methyl to methylene groups. Heteroatoms adjacent to these groups result in characteristic group frequencies: 126 7. GENERAL OUTLINE AND STRATEGIES FOR IR AND RAMAN SPECTRAL INTERPRETATION

The methoxy group has one band at ca. 2835 cm 1, methyl and methylene groups next to the nitrogen atom in tertiary amines result in bands at ca. 2800 cm 1, and aldehydes result in two peaks near 2730 cm 1 (due to Fermi resonance).

4.4. Acidic Protons: 3100e2400 cmL1

Broad bands in this region are typically due to acidic and strongly hydrogen-bonded hydrogen atoms. In general, IR is a much better technique than Raman spectroscopy for these groups. Hydrogen bonding is an important determinant in the frequencies for these groups. The main OH stretching band for carboxylic acid dimers is found at ca. 3000 cm 1 with additional overtone/combination bands at ca. 2650 cm 1 and 2550 cm 1. Primary, secondary, and þ tertiary amine salts absorb in this region and have distinctive band structure. The NeH stretch for these groups are characterized by moderate-to-strong IR and Raman bands. e þ Primary amine salts for the NH3 have an absorption band(s) between 3350 and 1 > þ > þ ¼ þ 3100 cm . Amines with NH2 , NH , and C NH have bands between 2700 and 2250 cm 1. Phosphoric acids have broad absorption bands in this region.

4.5. SH, BH, PH, and SiH: 2600e2100 cmL1

Both IR and Raman can be very useful for these species. The SH stretch for mercaptans and thiophenols occurs in the region 2590e2540 cm 1 and is generally quite strong in the Raman spectrum, but weak in the IR. BH stretches occur in the region 2630e2350 cm 1 and are moderate to strong in the IR spectrum, but are generally weak in the Raman spectrum. PH stretches occur in the region 2440e2275 cm 1 and are moderately intense in the IR spectrum and moderate to weak in the Raman spectrum. SiH stretches occur in the region 2250e2100 cm 1 and are strong in both the IR and Raman spectrum.

4.6. Triple Bonds and Cumulated Double Bonds: 2300e1900 cmL1

Both IR and Raman can be very useful for these species. The IR and Raman intensities for the XhY and X¼Y¼Z stretching vibrations are variable. Refer to chapter 6 (section 3.2) to use the table and idealized spectra (Figure 6.11 and table 6.3). Contributions from atmospheric carbon dioxide generate a false signal in this region of the IR spectrum.

4.7. Carbonyl-Containing Species: 1900e1550 cmL1

IR is excellent for carbonyl species while Raman is quite variable. The carbonyl C¼O stretching vibration results in strong characteristic IR bands. Raman bands for this vibration are typically moderate to weak with some structures resulting in a strong C¼O stretch. This band is easily identiﬁed in the IR spectrum because of its intensity and its lack of interference from most other group frequencies. Carbonyl groups are present in many different compounds such as ketones, carboxylic acids, aldehydes esters, amides, acid anhydrides, acid halides, lactams, lactones, urethanes, and carbamates. Bands above 1775 cm-1 are often due to carbonyl compounds such as anhydrides (doublet), acid halide, or strained ring carbonyl (such as lactones and carbonates in ﬁve-membered rings). Bands between INTERPRETATION GUIDELINES AND MAJOR SPECTRAeSTRUCTURE CORRELATIONS 127

1750 and 1700 cm 1 fall in the middle of the carbonyl range. Carbonyl compounds in this region can include aldehydes, esters, carbamates, ketones, and carboxylic acids. Bands below 1700 cm 1 fall in the low end of the carbonyl range. Such carbonyl compounds can include amides, ureas, and carboxylic acid salts. Since conjugation can lower carbonyl frequencies, this range will also include conjugated aldehydes, ketones, esters, and carboxylic acids. In general, bands below 1600 cm 1 are due to the out-of-phase stretch of carboxylic acid salts. The remaining carbonyl signals are due to C¼O stretches and occur above 1600 cm 1. Fermi resonance sometimes gives rise to two bands in the C¼O stretching region even though only one C¼O bond is present. See Chapter 2 for an explanation of this effect.

4.8. Oleﬁnic (C[C), Imino (C[N), and Azo (N[N) Compounds: 1690e1400 cmL1

The stretching vibrations of these groups are characterized by strong Raman band which makes Raman an excellent technique for these types of compounds. The intensities of the IR absorptions are variable. The C¼C stretching vibrations result in variable IR intensities. Most oleﬁn C¼C stretching bands occur between 1680 and 1600 cm 1. In IR this results in a narrow, weak absorption band. Conjugation with another double bond lowers the frequency and often increases the IR band intensity. Imino (C¼N) stretching vibrations result in strong Raman and moderately strong IR bands. Most C¼N stretching vibrations occur between 1690 and 1630 cm 1. Azo (N¼N) stretching vibrations give rise to strong, well-deﬁned Raman bands, but a very poor quality IR bands. Most Azo N¼N stretching bands occur between 1580 and 1400 cm 1. The nature of the compound is very important in analyzing spectra of azo species. Symmetrically substituted trans azo compounds give rise to strong Raman bands. Although the signal is forbidden in the IR, non-symmetrically substituted trans azo compounds can give rise to strong IR signals.

4.9. Organic Nitrates (N[O): 1660e1450 cme1 e e These species include nitro (R NO2), organic nitrates (R NO2), organic nitrites (ReOeN¼O), and nitroso groups. The N¼O stretching vibrations result in strong IR bands and generally moderate Raman bands. Aliphatic and aromatic nitro compounds have two IR e e strong bands between 1580e1475 cm 1 and 1390e1320 cm 1. Organic nitrites have two e e strong IR bands between 1660e1615 cm 1 and 1300e1270 cm 1. Only the lower band is observed by Raman spectroscopy. Inorganic nitrate salts (NO3 ) provide a broad band asso- e1 ciated with the out-of-phase NO3 between 1410 and 1350 cm (IR strong, Raman moderate). Organic nitrites provide strong IR and Raman bands with generally two bands resulting e because of rotational isomers. The cis form exhibits a band in the region 1625e1610 cm 1 e while the trans form exhibits a band in the region 1680e1650 cm 1. Nitroso groups are characterized by strong IR and Raman bands. In the solid and liquid state, nitroso groups exist as dimers in either the cis or trans state. The aliphatic cis form results in two bands: e e 1425e1330 cm 1 and 1345e1320 cm 1. The trans form results in a single band in the region e e 1290e1175 cm 1. The aromatic cis form results in two bands: 1400e1390 cm 1 and e e 1410 cm 1. The trans form results in a single band in the region 1300e1250 cm 1. 128 7. GENERAL OUTLINE AND STRATEGIES FOR IR AND RAMAN SPECTRAL INTERPRETATION 4.10. Amine NH Deformation Vibrations for Amines, Amine Salts, and Amide Compounds: 1660e1500 cme1

NH deformation bands result in moderate IR bands and weak Raman bands. Primary e e1 amine NH2 in-phase deformation occurs in the region 1660 1590 cm . Amine salts result þ e1 þ in a NH2 in-phase deformation band found between 1620 and 1560 cm while a NH3 e out-of-phase deformation results in two sets of bands between 1635e1585 cm 1 and e 1585e1560 cm 1. In secondary carbamates and mono-substituted amides, the CNH group e results in a strong IR band between 1570 and 1510 cm 1. Note that water also has a band e near 1640 cm 1 from the OH deformation.

4.11. Aromatic and Hetero-aromatic Rings: 1620e1420 cme1

Sharp bands in this region involve the aromatic ring quadrant and semi-circle stretching vibrations. The IR intensities for these bands are variable in intensity. The Raman intensities are moderate for the quadrant stretch and quite weak for the semi-circle stretching bands. Typically two sets of bands are observed in this region due to the quadrant and semi-circle ring stretch vibrations. These may occur as single bands or as a multiple component envelop of bands. e In general, the quadrant stretch will result in bands near 1600 and 1580 cm 1 while the e semi-circle stretch will result in bands near 1500 and 1460 cm 1 The relative intensity of the IR bands will vary with the aromatic substituent pattern and type of substituent. Six- membered ring heteroaromatics resulting from substituting an aromatic carbon atom with a nitrogen atom result in similar characteristic ring-stretching bands between 1600 and e 1500 cm 1. These include single nitrogen-substituted aromatic molecules such as pyridines, quinolines, and isoquinolines, two nitrogen-substituted aromatic molecules such as pyrimidines and quinazolines, and three nitrogen-substituted molecules such as triazine species. Simple aromatic compounds will also generate a series of weak IR absorption bands between e 2000 and 1700 cm 1 which derive from multiple combination bands.

4.12. Methyl and Methylene Deformation Vibrations: 1500e1250 cme1

These alkane deformation vibrations results in moderate IR bands and weak to moderate Raman bands. When these groups have identical substituents then the CH2 “scissors” deformation and CH3 out-of-phase deformation are found in the same frequency region, ca. e e1 1480 1430 cm . When the CH2 and CH3 are on hydrocarbons, this band is near e1 1460 cm . When the CH2 (methylene) is near an unsaturated group, the deformation e band is found near 1440 cm 1. If the methylene is adjacent to chlorine, bromine, iodine, sulfur, phosphorus, nitrile, nitro, or carbonyl, this band occurs between 1450 and e1 1405 cm . The CH3 in-phase deformation is a useful moderately intense IR band, but provides only a weak Raman band. The CH3 in-phase (“umbrella”) deformation is strongly dependent upon the electronegativity of the adjacent atom. The more electronegative the e atom, the higher the frequency with a range of 1470e1250 cm 1. Examples include e e1 e e1 e e1 O CH3 at ca. 1450 cm ,C CH3 at ca. 1450 cm , and Si CH3 at ca. 1265 cm . In aliphatic groups, steric hindrance to the vibrations due to the presence of two or three adjacent methyl INTERPRETATION GUIDELINES AND MAJOR SPECTRAeSTRUCTURE CORRELATIONS 129

e groups can result in highly characteristic bands. Here C CH3 results in a single band at e1 1378 cm , while the isopropyl C(CH3)2 has an equal intensity doublet at 1385 and e1 e1 1368 cm , and the t-butyl C(CH3)3 has a non-equally intense doublet at 1395 and 1368 cm .

4.13. Carbonate, Nitrate, Ammonium, and BeO Type Compounds: 1480e1310 cme1

Inorganic carbonate, nitrate, and ammonium ions provide a broad, intense IR band near e1 1400 cm but only a weak Raman band. IR bands result from the out-of-phase XY3 stretch for carbonate- and nitrate-containing compounds. Strong sharp Raman bands in the e e1 1040 1100 cm region result from the in-phase XY3 stretch. The ammonium ion deforma- þ e e1 tion band is due to a NH4 bend and is found in the 1480 1390 cm region. The BeO stretch provides a strong characteristic IR band. Inorganic boric acid has a strong e1 broad band near 1410 cm due to the BO3 out-of-phase stretch. Organic borates [B(RO)3], e boronates [PhB(RO)2], metaborates (cyclic six-membered B O ring), boronic acid esters, e and anhydrides are all characterized by strong IR bands in the region 1390e1310 cm 1 involving the BeO stretch.

4.14. Organic and Inorganic SOx Type and Thiocarbonyl (C[S) Compounds: 1400e900 cme1

In general, both IR and Raman provide strong characteristic bands associated with SOx ¼ 2e and C S stretching vibrations. Inorganic SOx type compounds include sulfites (SO3 ), 2e sulfates (SO4 ) as well as more complex SXOY type compounds (thiosulfate, pyrosulfite, dithionate). Sulfites have a strong broad IR band and a strong doublet Raman band between e1 1010 and 900 cm involving the SO3 out-of-phase and in-phase stretching vibrations. e Sulfates are characterized by a very strong IR band between 1130 and1080 cm 1 involving e2 e1 the SO4 out-of-phase stretch and a strong Raman band between 1065 and 955 cm e2 involving the SO4 in-phase stretch. SXOY type compounds are characterized by strong IR e and Raman bands between 1250 and 1000 cm 1 involving complex S¼O stretching vibrations. > ¼ > e Organic SOX type compounds include S O, SO2 as well as sulfonic acids ( SO3H), and e e þ sulfonic acid salts ( SO3 M ) (See chapter 6, section 8). In general, the stretching frequencies involving the S¼O group of these types of compound show a dependence on the electroneg- > ¼ ativity of the substituents. Sulfoxides (R2 S O) are characterized by a strong IR band and e a moderate-to-weak Raman band between 1070 and 1030 cm 1 from the S¼O stretch. Simi- larly, sulfinic acids (eS(¼O)eOH) are characterized by a very strong IR and moderate-to- e strong Raman band in the region 1090e990 cm 1 due to the S¼O stretch. The S¼O stretch is shifted to higher frequencies for sulfinic acid esters (RdS(¼O) dOeR) at e e1 ¼ 1140 1125 cm (strong IR; moderate intensity Raman) and dialkyl sulfites ((RO)2S O) in e e1 d d the region 1220 1170 cm (strong IR; strong, polarized Raman). Sulfones (R SO2 R) are characterized by two vibrations, an out-of-phase and in-phase stretch of the SO2 group. In most cases, strong IR bands result for both in-phase and out-of-phase vibrations while > a strong Raman band only occurs for the in-phase SO2 stretch. Sulfones ( SO2) have strong e e1 e e1 d d h characteristic bands at 1360 1290 cm and 1200 1120 cm . Sulfanamides (R SO2 N ) 130 7. GENERAL OUTLINE AND STRATEGIES FOR IR AND RAMAN SPECTRAL INTERPRETATION

e e have strong bands at 1360e1315 cm 1 and 1180e1140 cm 1. The higher frequencies are due to the inﬂuence of the more electronegative nitrogen atom. d d e e1 e e1 Sulfonyl halides ( SO2 X) have strong bands at 1385 1360 cm and 1190 1160 cm . The out-of-phase SO2 stretch results in a moderate-to-strong Raman band. Covalent sulfonates d d e d d e e e1 (R SO2 OR) and organic sulfates ( O SO2 O ) have bands at 1420 1330 cm and e e1 d d e þ 1200 1145 cm . Organic sulfate salts (RO SO2 O M ) are characterized by a strong IR e e band in the region 1315e1210 cm 1 and a strong Raman band in the region 1140e1050 cm 1. d d e þ Organic sulfonic acids ( SO3H) and salts ( SO3 M ) are characterized by strong IR and d Raman bands involving the SO2 and SO3 stretching vibrations. Sulfonic acids ( SO3H), if not d e dried, are easily ionizable with small amounts of water resulting in a hydrated form ( SO3 þ e d H3O ). Anhydrous sulfonic acids (R SO2 OH) have strong IR and Raman bands at e e1 e e1 1355 1340 cm and 1200 1100 cm from the SO2 out-of-phase and in-phase stretches, e þ e e1 respectively. Hydrated sulfonic acids (RSO3 H3O ) have bands at 1230 1120 cm and e e1 1120 1025 cm from the SO3 out-of-phase and in-phase stretches, respectively. Both SO3 vibrations result in strong IR bands. However, a moderate-to-strong Raman band is observed d e þ only for the SO3 in-phase stretch. Sulfonic acid salts ( SO3 M ) have bands at e e1 e e1 1250 1140 cm and 1070 1030 cm . The out-of-phase SO3 stretch results in very strong IR bands but weak Raman bands. However, the in-phase SO3 stretch results in strong IR and Raman bands. Thiocarbonyl compounds (>C¼S) are generally characterized by a strong IR and Raman e band between 1250 and 1200 cm 1 that involve the C¼S stretch.

4.15. P[O-Containing Compounds: 1350e1080 cme1

The P¼O stretching vibration for organic phosphorus compounds results in a strong IR e band between 1350 and 1140 cm 1 while the Raman band intensity is moderate to weak. The frequency of the P¼O stretch shows a strong dependence on the substituent electronegativity and hydrogen bonding effects. Inorganic POx type compounds include dibasic 2e e 3e phosphate (HPO4 ), monobasic phosphate (H2PO4 ), phosphate (PO4 ). The phosphate out- e of-phase stretch has strong IR and Raman bands between 1180 and 1000 cm 1. The dibasic d 2e e1 phosphate (HO PO3 ) has strong IR and Raman bands between 1150 and 1000 cm from e the PO3 out-of-phase stretch. The monobasic phosphate ((HO)2 PO2 ) has strong IR and Raman e1 ¼ bands between 1200 and 950 cm from the PO2 out-of-phase stretch. The P Obandcan appear as a doublet, possibly due to Fermi resonance or, in some cases, rotational isomerism.

4.16. Fluorinated Alkane Groups: 1350e1000 cme1

The CeF stretch of organic fluorine compounds results in strong IR bands but weak to moderately intense Raman bands. Monofluorinated compounds have a strong IR and e a weak to moderate Raman band between 1100 and 1000 cm 1. Difluorinated compounds d d e1 ( CF2 ) have two very strong IR bands between 1250 and 1050 cm involving the CF2 out-of-phase stretch. These bands are weak to moderate in the Raman spectrum. Trifluori- d e1 nated compounds ( CF3) have multiple strong bands between 1350 and 1050 cm d involving the CF3 out-of-phase stretch. Fluorine substituted aromatics (Ar F) have a moder- e ately strong IR band between 1270 and 1100 cm 1 involving the aryl ring CeF stretch. INTERPRETATION GUIDELINES AND MAJOR SPECTRAeSTRUCTURE CORRELATIONS 131 4.17. CeO Stretching Vibrations: 1300e750 cme1

e Bands in the region 1300e750 cm 1 are associated with the CeO stretch of species such as alcohols, ethers, esters, carboxylic acids, and anhydrides. Ethers are characterized by CdOdC out-of-phase and in-phase stretches. In general, the out-of-phase CeOeC stretch e results in strong IR bands in the range 1270e1060 cm 1 but weak Raman bands. The in-phase e CeOeC stretch results in strong Raman bands and moderate IR bands at 1140e800 cm 1. e Alcohols are characterized by CeO type stretch vibrations in the region 1200e750 cm 1. e Primary alcohols are characterized by a strong IR band between 1090 and 1000 cm 1 and e a strong Raman band between 900 and 800 cm 1. Secondary alcohols are characterized by e multiple strong IR bands between 1150 and 1075 cm 1 and a strong Raman band between e 900 and 800 cm 1. Tertiary alcohols are characterized by multiple strong IR bands between e e 1210 and 1100 cm 1 and a strong Raman band between 800 and 750 cm 1. Carbonyl compounds such as esters, carboxylic acids, and anhydrides include a CeO group that is often used to conﬁrm the functional group. The CeO stretch of carboxylic acids e is characterized by moderately intense IR bands in the range 1380e1210 cm 1 with the corresponding Raman bands having highly variable intensity. Similarly, esters result in strong IR e bands between 1300 and 1100 cm 1 and corresponding Raman bands of variable intensity. e Anhydrides are characterized by strong IR and Raman bands between 1310 and 980 cm 1 involving the CeOeC stretching vibrations.

4.18. SieO and PeO Containing Compounds: 1280e830 cme1

The SieO group is characterized by strong IR bands and variable Raman bands. Compounds containing PeOeC group are characterized by bands in the range e 1090e920 cm 1 which involve the out-of-phase stretching vibration. These characteristic bands are typically strong in the IR and moderate to weak in the Raman spectrum. The PeOeP and PeOH groups are characterized by strong IR bands but only moderate-to- weak Raman bands. e The PeOeP group is characterized by a strong IR band between 1025 and 870 cm 1 involving the PeOeP out-of-phase stretch. The PeOH group is characterized by bands e involving the PeO stretch between 1000 and 900 cm 1 with strong IR intensity, but moderate-to-weak Raman intensity. The siloxane SieOeSi and SieOH groups are characterized by strong IR bands at e e 1090e1010 cm 1 and 955e830 cm 1, respectively, involving the SieO stretch. Raman spectra of siloxanes do not provide useful bands in this region. Alkoxysilanes, SieOeR, are charac- e terized by an out-of-phase stretch (1110e1000 cm 1) which results in a strong IR band and an e in-phase stretch (1070e990 cm 1) which results in moderate-to-strong intensity IR and Raman bands.

4.19. CH Wag of Oleﬁnic and Acetylenic Compounds: 1000e600 cme1

The CH wag vibration provides important medium-to-strong IR bands for characterizing alkenes and acetylenes. These bands are typically weak in the Raman spectrum. The position of these bands is dependent on the properties (electron withdrawing) of the substituents. 132 7. GENERAL OUTLINE AND STRATEGIES FOR IR AND RAMAN SPECTRAL INTERPRETATION

e ¼ e e1 Vinyl groups, CH CH2, have strong IR bands between 1000 940 cm and e e e 960e810 cm 1 (995e980 cm 1 and 915e905 cm 1, respectively, for hydrocarbons). Vinylidene > ¼ e1 e e1 groups, C CH2, exhibit strong IR bands between 985 and 700 cm (895 885 cm for hydrocarbons). Trans-di-substituted ethylenes, eCH¼CHe, have strong IR bands between 980 and e e 890 cm 1 (1000e955 cm 1 for hydrocarbons). Vibrational interaction with conjugated diene groups results in a systematic increase in the observed CH wag. An isolated trans alkene (T) e e has a CH wag at 965 cm 1, a conjugated transetrans diene (TT) at 986 cm 1, the transetranse e e trans alkene (TTT) at 994 cm 1, and the transetransetransetrans alkene (TTTT) at 997 cm 1. e Cis-di-substituted ethylenes have strong IR bands between 800 and 600 cm 1 e (730e650 cm 1 for hydrocarbons). Tri-substituted alkenes, >CH¼CHe, absorb between e 850 and 790 cm 1. The CH wag of acetylenic, ChCH, have moderate-to-strong IR bands e between 700 and 578 cm 1.

4.20. Aromatic In-plane 2,4,6 Radial Carbon In-phase Stretch: 1290e990 cme1

Very strong Raman bands are observed from aromatic ring vibrations involving the 2,4,6 e radial carbon in-phase stretch. A very strong Raman band between 1010 and 990 cm 1 is observed for mono-, 1,3 di-, and 1,3,5 tri-substituted benzenes. Only a weak to moderately intense sharp IR band is observed.

4.21. Aromatic CH Wag: 900e700 cme1

The aromatic ring CH wag vibrations results in strong IR absorption bands but only weak Raman bands. The frequencies of the aromatic CH wag are largely dependent upon the number of adjacent hydrogen atoms since the adjacent CH wag vibrations are mechanically coupled to one another. For this reason, the IR bands from the in-phase CH wag vibrations are quite useful in distinguishing aromatic ring substitutions. e Mono-substituted benzenes have a band at ca. 750 cm 1 involving the ﬁve adjacent CH e wag (overall region between 820 and 728 cm 1). Ortho di-substituted benzenes also have e a band at ca. 750 cm 1 involving the four adjacent CH wag (overall region between 790 e and 728 cm 1). The three adjacent CH wag vibrations of meta- or 1,2,3 tri-substituted e e benzenes have a band at ca. 782 cm 1 (overall region between 825 and 750 cm 1). The two adjacent CH wag vibrations of para, 1,2,4 tri-substituted, or 1,2,3,4 substituted benzenes e e have a band at ca. 817 cm 1 (overall region between 880 and 795 cm 1). The lone CH wag vibration (meta, or 1,2,4,. or 1,3,5,. or 1,2,3,5,. or 1,2,4,5,. or penta) substituted benzenes e e have a band at ca. 860 cm 1 (overall region between 935 and 810 cm 1). The aryl CH adjacent classiﬁcation can also be extended to pyridines and napthalenes.

4.22. Halogen-Carbon Stretch: 850e480 cme1

Strong IR and Raman bands result for the halo-alkanes involving the CeX stretching vibrations (X¼F, Cl, Br, I). Fluoroalkanes are summarized above. The CeCl stretching INTERPRETATION GUIDELINES AND MAJOR SPECTRAeSTRUCTURE CORRELATIONS 133

e vibrations occur between 860 and 505 cm 1. Compounds with more than one chlorine atom e ¼ will have multiple bands deriving from the in-phase and out-of-phase C Clx (X 2,3,4) which may also couple with other groups. The CeBr stretching vibrations occur between e 680 and 485 cm 1. Compounds with more than one bromine atom will have multiple bands e deriving from the in-phase and out-of-phase C Br2 which may also couple with other e groups. The CeI stretching vibrations occur between 610 and 485 cm 1.

e1 4.23. OH, NH, NH2 Wag: 900e500 cm In the condensed state, moderately intense (but broad) IR bands are found between 900 e and 500 cm 1 due to the XeH wag of hydrogen-bonded water, amines, amides, and alcohols. Hydrogen bonding significantly influences the frequency for these characteristic IR bands. No significant Raman bands from these vibrations are observed. Alcohols exhibit bands e e that are generally centered around 650 cm 1. Water absorbs below 800 cm 1. e Primary amines have bands between 900 and 770 cm 1 and secondary amines between 750 e e and 680 cm 1. Amides have bands between 750 and 550 cm 1.

4.24. Metal Oxides: 800e200 cme1

Metal oxides of various types have strong IR and Raman bands from the metal-O-metal group.

CHAPTER 8

Illustrated IR and Raman Spectra Demonstrating Important Functional Groups

The IR and Raman spectra of each compound are presented in a stacked format with the spectrum number given in the upper right-hand corner of each IR spectrum. The sample preparation and type of crystal used for the IR measurement is listed in parenthesis after the compound name in the spectral index below. The IR measurements were made using a Bio- Rad FTS-575C spectrometer. All Raman measurements were made using 180o backscattering on a BioRad FT-Raman spectrometer (575C with Raman III accessory) and background corrected using a KBr white light reﬂectance measurement. A melting point or NMR tube was used for the Raman measurements. A single bounce diamond ATR accessory was used for the IR measurements of the polymers. The assignment shown on all of the spectra are consistent with that discussed in the text. Page numbers of spectra are shown on the right hand side. 1. ALIPHATIC

1. Heptane, [IR: capillary film/ZnSe], 140 2. Cyclohexane, [IR: capillary film/ZnSe], 140 3. Isooctane (2,2,4-Trimentyl pentane), [IR: capillary film/KBr], 140 2. C[C DOUBLE BONDS

4. 1-Hexene, [IR: capillary film/KBr], 141 5. cis-3-Heptene, [IR: capillary film/KBr], 141 6. trans-3-Heptene, [IR: capillary film/KBr], 141 3. TRIPLE BONDS

7. Acetonitrile, [IR: capillary film/KBr], 142 8. Acrylonitrile, [IR: capillary film/KBr], 142 9. 1-Octyne, [IR: capillary film/KBr], 142

135 136 8. ILLUSTRATED IR AND RAMAN SPECTRA DEMONSTRATING IMPORTANT FUNCTIONAL GROUPS 4. AROMATIC RINGS

10. Toluene, [IR: capillary film/ZnSe], 143 11. o-Xylene, [IR: capillary film/KRS5], 143 12. m-Xylene, [IR: capillary film/KRS5], 143 13. p-Xylene, [IR: capillary film/KBr], 144 14. m-Tetramethyl xylene diisocyanate, [IR: smear/KBr], 144 15. Pyridine, [IR: capillary film/KRS5], 144

5. KETONES, ESTERS, AND ANHYDRIDES

16. Acetone, [IR: capillary film/KBr], 145 17. n-Butyl acetate, [IR: capillary film/KBr], 145 18. Dimethyl carbonate, [IR: capillary film/KBr], 145 19. Dimethyl malonate, [IR: capillary film/KBr], 146 20. Dimethyl terephthalate, [IR: KBr disc], 146 21. Butyric anhydride, [IR: capillary film/KBr], 146 22. Maleic anhydride, (Furan-2,5-dione) [IR: KBr disc], 147 23. 4-Hydroxy benzaldehyde, [IR: KBr disc], 147 24. Glycolic acid, (2-Hydroxyacetic acid) [IR: KBr disc], 147 25. Palmitic acid, [IR: KBr disc], 148 26. Oleic acid, (Z-Heptadec-9-enoic acid): [IR: capillary film/KBr], 148 27. Benzoic acid, [IR: KBr disc], 148 28. Stearic acid, calcium salt, [IR: KBr disc], 149 29. Glycine (Zwitterion), (2-Aminoacetic acid) [IR: KBr disc], 149

6. AMIDES, UREAS, AND RELATED COMPOUNDS

30. Acetamide, [IR: methanol cast film/KRS5], 149 31. Acrylamide, [IR: KBr disc], 150 32. N-butyl methyl acrylamide, [IR: smear/KRS5], 150 33. 1,3-Dimethyl urea, [IR: KBr disc], 150 34. Ammeline, (4,6-Diamino-1,3,5-triazin-2(1H)-one) [IR: KBr disc], 151 35. Trimethyl isocyanurate, (1,3,5-Trimethyl-1,3,5-triazinane-2,4,6-trione) [IR: KBr disc], 151 36. 2-Imidazolidone, (Imidazolidin-2-one) [IR: methylene chloride cast film/KRS5], 151 37. Dimethyl formamide, [IR: capillary film/ZnSe], 152 38. Ethyl carbamate, [IR: methanol cast film/KRS5], 152 39. Acetohydroxamic acid, (N-Hydroxyacetamide) [IR: KBr disc], 152 COMPOUND INDEX 137 7. ALCOHOLS

40. Methanol, [IR: capillary film/KBr], 153 41. Isopropyl alcohol, (Propan-2-ol) [IR: capillary film/KBr], 153 42. t-Butyl alcohol, (2-Methylpropan-2-ol) [IR: capillary film/KBr], 153 43. 1-Butanol, [IR: smear/KRS5], 154 44. 1-Hexadecanol, [IR: methylene chloride cast film/ZnSe], 154 45. Phenol, [IR: melt/KRS5], 154 46. 2,6-Di-t-butyl phenol, [IR: methylene chloride cast film/ZnSe], 155 47. Diethylene glycol, (2,2’-oxydiethanol) [IR: smear/ZnSe], 155

8. ETHERS

48. n-Dibutyl ether, (1-Butoxypentane) [IR: capillary film/ZnSe], 155 49. Tetrahydrofuran, [IR: capillary film/ZnSe], 156 50. Epichlorohydrin, (2-(chloromethyl)oxirane) [IR: capillary film/ZnSe], 156

9. AMINES AND AMINE SALTS

51. Isobutyl amine, (2-Methylpropan-1-amine) [IR: capillary film/ZnSe], 156 52. Aniline, [IR: capillary film/KRS5], 157 53. n-Dibutyl amine, (n-Butylpentan-1-amine) [IR: capillary film/ZnSe], 157 54. n-Tributyl amine, (N,N-Dibutylpentan-1-amine) [IR: capillary film/ZnSe], 157 55. Trimethyl amine HCl, [IR: KBr disc], 158 56. Tetramethyl ammonium chloride, [IR: KBr disc], 158

10. C[N COMPOUNDS

57. Benzamidine HCl, [IR: KBr disc], 158 58. Acetamide oxime, (Z)-N’-Hydroxyacetimidamide [IR: KBr disc], 159 59. Pipenidindione dioxime, (2E,6E)-Piperidine-2,6-dione dioxime [IR: KBr disc], 159

11. N[O COMPOUNDS

60. Isoamyl nitrate, [IR: capillary film/KBr], 159 61. 2-nitropropane, [IR: capillary film/KBr], 160 62. Isopropyl nitrate, [IR: capillary film/KBr], 160 138 8. ILLUSTRATED IR AND RAMAN SPECTRA DEMONSTRATING IMPORTANT FUNCTIONAL GROUPS 12. AZO COMPOUND

63. Azo-tert-butane, (E)-1,2-di-tert-butyldiazene [IR: capillary ﬁlm/KBr], 160

13. BORONIC ACID COMPOUND

64. meta-tolyl boronic acid, [IR: Nujol mull/KBr], 161

14. CHLORINE, BROMINE, AND FLUORINE COMPOUNDS

65. 1-Chlorooctane, [IR: capillary film/KBr], 161 66. 1-Bromohexane, [IR: capillary film/KBr], 161 67. 3-Fluorotoluene, (1-Fluoro-3-methylbenzene) [IR: capillary film/KBr], 162 68. 3-Chlorotoluene, (1-Chloro-3-methylbenzene) [IR: capillary film/KBr], 162 69. 3-Bromotoluene, (1-Bromo-3-methylbenzene) [IR: capillary film/KBr], 162

15. SULFUR COMPOUNDS

70. Dimethyl sulfoxide, (Methylsulﬁnylmethane) [IR: capillary ﬁlm/KBr], 163 71. Methane sulfonic acid, sodium salt, [IR: Nujol/Fluorolube mixed mull on KBr], 163 72. para-Toluene sulfonic acid hydrate, [IR: KBr disc], 163 73. Dodecyl sulfate, sodium salt, [IR: Nujol/Fluorolube mixed mull on KBr], 164 74. Sodium isopropyl xanthate, [IR: KBr disc], 164 75. Zinc dimethyl dithiocarbamate, [IR: KBr disc], 164 76. 2-Imidazolidinethione, (Imidazolidine-2-thione) [IR: KBr disc], 165

16. PHOSPHORUS COMPOUNDS

77. Triphenyl phosphine, [IR: KBr disc], 165 78. Tributyl phosphite, [IR: capillary film/KBr], 165 79. n-Dibutyl phosphite, [IR: capillary film/KBr], 166 80. Sodium di-isobutyl dithiophosphate, [IR: water cast film/KRS5], 166

17. SILOXANE COMPOUNDS

81. Siloxane polymer (silicone grease), [IR: smear/KBr], 166 COMPOUND INDEX 139 18. INORGANIC COMPOUNDS

82. Ammonium chloride, [IR: KBr disc], 167 83. Sodium sulfate, [IR: KBr disc], 167 84. Sodium sulﬁte, [IR: KBr disc], 167 85. Sodium carbonate, [IR: KBr disc], 168 86. Sodium bicarbonate, [IR: KBr disc], 168 87. Potassium nitrate, [IR: KBr disc], 168 88. Tribasic sodium phosphate, [IR: KBr disc], 169 89. Dibasic sodium phosphate, [IR: KBr disc], 169 90. Boric acid, [IR: KBr disc], 169 91. Sodium perchlorate, [IR: KBr disc], 170 92. Sodium molybdate, [IR: KBr disc], 170 93. Silica gel, [IR: KBr disc], 170 94. Talc, [IR: ATR], 171

19. POLYMERS AND BIOPOLYMERS

95. Isotactic polyethylene, [IR: ATR], 171 96. Polybutadiene, [IR: ATR], 171 97. Polyvinyl alcohol (PVA), [IR: ATR], 172 98. Polyethylene oxide, [IR: ATR], 172 99. Polytetrafluoroethylene (Teflon), [IR: ATR], 172 100. Poly acrylic acid, [IR: ATR], 173 101. Polyvinyl pyrrolidone, [IR: ATR], 173 102. Nylon 6,6, [IR: ATR], 173 103. Cellulose, [IR: ATR], 174 104. Starch, [IR: ATR], 174 105. Sodium carboxymethyl cellulose, [IR: ATR], 174 106. Hydroxypropylmethyl cellulose, [IR: ATR], 175 107. Ethyl cellulose, [IR: ATR], 175 108. Siloxane polymer, [IR: cap film/KBr], 175 109. Poly acrylamide (PAM), [IR: water cast film/ZnSe], 176 110. Poly-2-(acryloyloxy)-Ethyltrimethyl Ammonium Chloride (AETAC), [IR: water cast film/ZnSe], 176 140 8. ILLUSTRATED IR AND RAMAN SPECTRA DEMONSTRATING IMPORTANT FUNCTIONAL GROUPS

100 1 80

IR 60 723

%T 1379 40 CH2 i. ph. rk. CH3 i. ph. 20 1466 bend CH 3 (CH2)5 CH 3 2859 2959

CH , CH str. CH bend + BBB CH 2 3 2 CH B B 3 2875 2 C-C-C

2937 CH o. ph. bend o.ph. 3 i. ph. Heptane o. ph. str

0.1 str twist 310 1451 902 2963 394 1302 840 357 Ra 1138 1081 1046 2733 776 I 0.0 100

80 2 IR 60 1039 1257 862 904

%T 2793 2660 40 S 20 1450 2853 2925

0.8 CH i.ph. str. 2 802 CH2 o.ph. str. CH2 bend 2853 Cyclohexane

Ra 2938 0.4 I Ring i. ph. str. 1029 1267 1445 427 1157 1348 2665

0.0

100 isopropyl 3 80

IR 980 60 %T 1248 1169 1393 CH3 40 CH3 CH3 2871 1469 1366 CH CH CCH 20 i. ph. bend. 2 3 CH

2956 3 t-butyl CH3 2902

CH3 CH3 i. ph. str. CH3 C C o. ph. str. o. ph. bend. CC 746 Isooctane C CC C 0.3 C i. ph. str.

2908 i. ph. str. 2957

Ra 0.2 2873 I 1452 513 303 0.1 929 827 1248 2715 1098 1353 1169 0.0 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumbers(cm–1) %T %T %T IR IR IR Ra Ra Ra I I I 100 100 100 0.0 0.1 0.2 0.0 0.1 0.0 0.1 0.2 20 40 60 80 20 40 60 80 20 40 60 80 o. ph. str. o. ph. str. HC=CH =CH str. =CH str. o. ph. str. o. ph. str. 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 i. ph.str. HC=CH =CH str. CH o. ph. str. o. ph. str. CH =CH o. ph. str. =CH CH 3 3 CH 2 3 2 3

2997 2963 3081 2965 2936 3027 3009 2963 3007 2961 3078 2936 3000 2876 2931 2932 2870 2875 2876 CH 2874 2730 2731 2735 2877 2 o. ph. str. CH CH 3 i. ph.str. 3 i. ph.str. C=C str. 2 x 910 2 x C ¼

1822 BONDS DOUBLE C Wavenumbers(cm C=C str. C=C str. 1642 1670 1655 1655 1642 CH CH CH CH bend CH 3 2 o. ph.bend bend + 3 2 1460 1460 1443 2 1459 1441 1450 o. ph.bend bend + 1441 =CH rk bend 1417 =CH –1 1379 1378 1380 ) CH CH 2

CH 1297

bend 1304 1297 1291 bend

3 1269 3

1248 bend i. ph. i. ph. 3 CH 1219 H i. ph. CC 2 1105 twist chain 1103 1067 1069 1069 1050 1058 1030 1020 H 993 966 970 968 915

908 trans o.pl. wag 897 910 866 870 875 H 852 820 808 CC 772 C C C H H 739 CH 3 3 709 711 H H H H i o. pl.wag cis H 7 7

629 2 632 CC CC CC

CH(CH 553 486 HH 467 CC H C H C 2 389 2 H ) 2 360 3 H H HH CH 4 5 6 326 312 5 311 5 141 3 trans-3-Heptene cis-3-Heptene 1-Hexene 142 8. ILLUSTRATED IR AND RAMAN SPECTRA DEMONSTRATING IMPORTANT FUNCTIONAL GROUPS

100 7 80 918 918 + 2254 + 1376 IR 750

60 3165 2945 3003 %T 918 2 X 380 bend 2293

40 1039 CH3 1444

o. ph. str. 1376 20 CH3 rk CH3 CH o. ph. N C CH 2254 3 3 i. ph. str. bend.

0.3 C≡N str. C-C str,

2943 CH3 i. ph. C-C-N Acetonitrile 2253 bend. bend 0.2 920

CH 380 Ra 3 o. ph. str. I 0.1 3715 3003 2293 1443 2884 2733 0.0

100 8

80 H H 1287 870 805 2280 IR 1655 CC 1609 1939 2990 3119 1094 %T 60 3071 H

2 x 969 H 687 40 =CH2 wag C cis CH wag C=C 1413 H

2229 + trans CH wag =CH2 str. str. H 20 =CH str. CC C≡N str. =CH H 2 969 bend H 0.3 H2CCC N

1610 H 2230 CC

i. pl. bend 241 Acrylonitrile 0.2 C-C str.

Ra 3035

I 1414 0.1 1287 872 568 689 3120 2991 1094 0.0 CH i. ph. bend 100 3 885 527 80 1687 1113 725 1327 1242

2120 9 1433 IR 1380 60 CH rk %T ≡ 3 1467

1460 2x C-H wag C≡C str. 40 ≡ C-CH2 bend 3314

20 629 2861 2958 2119 2934

CH2

1-Octyne 8 ≡C-H str. CH2 bend + ≡ CH2 i. ph. str. C-H wag o. ph. str. CH3 o. ph. bend

6 339

Ra 4 2930

I 1439 292 2851 1304 843 885 632 1114

2 810 1327 1077 1014 2731 3314 0 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber(cm–1) AROMATIC RINGS 143

100 10 2 x 1379 80 CH3 1735 896 1803 1858 IR 2735 1943 i. ph. 3086 1379 60 2872 %T bend 1080 CH3 Ring CH wag 1030 464 1461 40 1605 2921 summation bands Aryl CH3 o. ph. 20 CH str. bend 5 adj Aryl 3028 1496 CH i. ph. wag 729

Ring Semi. Str. 695 Toluene

O O O 0.8 Ring

Aryl CH i. ph. str. 1005 3 Quad. Str. + 2x 1461 cm-1 0.6 Aryl CH3 i. ph. bend 787 Ra 0.4 Aryl CH str. 1032 3056 I 219 523

2 x 1381 1211 0.2 2921 1606 623 1381 1158 2983 1438 2737 0.0 100 11 80

2 x 1383 582 1291 1942 505

IR 932 1223 1788 3105 2731 60 1900 %T CH3 i. ph. str. 40 + overtone 985 4 adj

1606 aromatic 1120 3063 2878 1383 CH wag 1020 20 435 1053 2940 CH3 o. ph. str. CH3 o. ph. bend 743 1496 1467 3017 o -Xylene

0.8 Ring Aryl CH3 CH3 Aryl Ring 735 CH i. ph. str. semi-circle i. ph. bend CH str. 3 Quad. str. CH3 0.6 + overtone Aryl CH CH o. 3 i. pl. bend 583

Ra ph. bend 1053 0.4 I 1223 257 2920 3045 506

2 x 1385 1385

0.2 1608 986 1158 1450 1291 1583 2733 0.0

100 12 80 515

IR 1250 1932 1854 1772 1653 905

60 2732 %T 2x 1377 1170 1095 876 40 lene 1377 1040 y Lone aryl 1460 20 2864 691 CH wag m -X 432 1612 3017 769

1492 3 adj CH wag 2921 O 0.5 Aryl Aryl CH i. ph. str. Ring Ring 3 726 1001 CH str. + 2x 1460 cm-1 Quad. str. semi-circle Aryl CH 538 3 O CH3 i. ph. bend

Ra 0.3 227

I 2919 516 1251 3051 278 1379

2865 CH

3 1612 1035 1171 1593 1095 1451 2733 0.0 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 400 600 Wavenumbers(cm–1) 144 8. ILLUSTRATED IR AND RAMAN SPECTRA DEMONSTRATING IMPORTANT FUNCTIONAL GROUPS

100 13 80 2x 1379 1793 2733 1630

IR 1891 60 1220 %T 3095 CH3 1379 1043 1119

40 1455 2869 CH o. ph. bend 2 adj.

3020 3 20 H wag

2923 Ring semi-circle str. CH3

Aryl CH str. 483 1517 795 0.6 O Aryl CH3 i. ph. str. Ring p -Xylene 830

+ 2x 1455 Quad. str 460 Aryl CH3 i. ph bend 1206 0.4 O 2922 Ra 812 I 313 3055 646 1380 0.2 1619 3014 2866 388 1184 1448 1314 2735 1580

0.0 100 14 80 2879 500 863 IR 929 3655 60 3058 633 %T 1606 580 1273 2936 1489

1423 Aryl lone 40 797 NCO Comb. 1086 CH wag 1368 706

20 2259 + 1157 2983 1416 CH3 Ring 3 adj. 1232

o. ph. str. 2259 semi-circle str. H wag CH3 i. ph bend

O NCO Aryl Ring NCO Quad. str NCO CH str. CH str. 1003 0.3 3 o. ph. str. i. ph. str O

Ra 0.2 NCO

I 685 2941 1416 565 262 2987 343 1443 1173 931 1088 1608 1276 m -Tetramethyl xylene diisocyanate 0.1 3071 795 2868 1463 1117 2724 2769 2256 0.0 100 H2O 15 80 H2O 885 3660 1988 1923 1873 IR 60 3002 %T 1634 1217 406 1148 1068

40 604 3079 3027 1483 3410 3054 992

20 1031 5 adj.

1439 H wag 749

Aryl CH str. 1582 705 1.0 N 993 N

Pyridine Ring Ring 0.8 Quad. str semi-circle str. N 1032 0.6 Ra Ring Quad. I 0.4 3059 i. pl. bend 654 1219 1575 606

0.2 1149 2957 3147 1486 0.0 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber(cm–1) KETONES, ESTERS AND ANHYDRIDES 145

100 16

80 530 + 1222 903 1283 3414 2925

IR 1093

60 3005 %T 530 1422 2 x 1716 1748 40 CH (C=O) 3 C-C-C O i. ph. str. o. ph. str. 20 CH3 CCH3 1222 1363 1716

CH3 i. ph. bend C=O 0.6 CH3 i. pl. rk. Acetone 2924 C=O str. CH o. ph. str. 3 788 o. ph. bend C-C-C i. ph. str. 0.4 Ra I 0.2 531 1710 3005 1429 390 1067 2848 1222 1358 899 2698 0.0

100 17

80 634 O 739 3463

607 C IR 951 O 60 O %T 1464 2 x 1743 C C=O 1387 1066 2876 CH (CH ) 40 (C=O) 3 2 O o. pl. wag i. ph. 1032 1367 C=O 20 bend O CH3 (CH2) CH (C=O) i. pl. rk.

2962 3 o. ph. str. CH C H 1244 O-CH str. OnC 1743 i. ph. bend 2 3 4 9

C-C-O o. ph. str. 0.12 2940 C=O str. Chain i. ph. 2877 n -Butyl acetate CH2 twist 0.08 635 308

Ra 839 1452

I 920 430 1303 1033 480 1739 1065 808 881 0.04 1124 2739 0.00

100 18 80 2857 1095 1605 3009 IR 60 1214 915 795 2963 CH 1435 %T 3 i. ph. 40 bend 970 O (O) CH str. O-C-O 20 3 CH3 O COCH3 1455 o. ph. str. 1277 1757 l carbonate y (O) CH 3 517 o. ph. bend C-O-C-O-C C=O str. 916 0.4 2964 i. ph. str. Dimeth

Ra 0.2 256

I 1458 367 3035 2888 2848 1212 1119 860 692 1754 970 1163

0.0 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber(cm–1) Butyric anhydride Dimethyl terephthalate Dimethyl malonate 146 %T %T %T Ra Ra Ra IR IR IR I I I 0.00 0.02 0.04 0.06 0.08 0.00 0.04 0.08 0.12 0.16 100 100 100 0.0 0.4 0.8 1.2 20 40 60 80 20 40 60 80 20 40 60 80 .ILSRTDI N AA PCR EOSRTN MOTN UCINLGROUPS FUNCTIONAL IMPORTANT DEMONSTRATING SPECTRA RAMAN AND IR ILLUSTRATED 8. 2 x 1720 2 x 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 o. ph. str. o. ph. str. (O) CH CH str. Aryl CH 3422 3473 3 3

3086 (O) CH + 2xbend 2941 CH 3006 2970 3042 3017 3000 2958 2961 2960 3 2959 i. ph.str. 2918 2940 3 2880 2845 str. 2844 2851 2850 2746 2880 C=O str. 2102 i. ph.str. i. phstr. C=O 1961 C=O

1819 impurity COOH 1905

1812 o. ph. str. 1757 Wavenumber(cm 1726 1720 1750 C=O 1751

1750 o. ph str. (O)CH bend +CH i.bend ph. (O) CH (O)CH o. ph. bend o. ph. 1740 1712 C=O i. ph. bend bend

CH 1610 3 3 Quad str. 2 3 1535 1462 Ring 1504 3

CH 1460 1453 1450 1435 1439 CH 1415 Semicircle str.

1413 o, ph. str.

bend 1415 1414 –1 i.bend ph. 2 1408 1387 C-C-O str. (C=O) C-C-O involves

bend )

2 1343 CH = 1301 1296 1280 (C=O) 1282 1278 3 1240 1190 1206 1140 1192 1157 1154

1117 1108 C-O-C 1099 C-O str. 1051 1108

1043 str. 1022 1016 1026 1030 961 994 involves 955 951 O-C str. 954

901 CH 930 916

843 2 adj. Aromatic 869 873 876 CH + C=O wag + C=O 3 847 851 CH (C 829 CH wag 792 798 814 3 787 OCCH 785 749 2

) 750

3 708 688 O 687 C O 635 730

570 O 563 574 580 2 C O

o o 498 460 C O (CH CH OO OCH 19 20 21 382 C C 3 353 2 354 272 ) 3

OO CH 308 293 CH 3 3 3 %T %T %T Ra Ra Ra IR IR IR I I I 100 100 100 0.0 0.1 0.2 0.0 1.0 2.0 3.0 0.0 1.0 2.0 20 40 60 80 20 40 60 80 20 40 60 80 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500

OH str. 3593 (CH H 2 O str. 3435 2 3294 )OH 3281 =CH str. CH str. Ar

CH 3169 3171 3122 3188 3123 AldehydeCH str. 2975 2 3066 3060 str.

(O=C)OH 2969 2947 2938 + 2xbend 2881 2880 str. 2831 2764 2791 2789 2647 (acid OHbondedtoalcO) 2565 i. ph.str EOE,ETR N ANHYDRIDES AND ESTERS KETONES,

2238 C=O C=O str. C=O str.

1933 Ar. Quadstr. 1906 1857 1842 1856 o. ph.str

1730 C=O Wavenumber(cm 1726 1787 1783 1713 1665 1666 C=C str. 1633 1634 1598 1594 1591 CH 1560 1586 1516 AldCH bend str. circle Semi Ar. 2 1460 bend 1453 1429 1432 1452 1434

–1 1388

1389 o. ph.str. C-C-O 1399 Ar-O str.

1360 o. ph.str. 1362 ) 1314 = 1290

C-C-O 1315

1286 = 1286 1268 1231 1250 1240 1219 1218 1242 1160 1108 1086 1164 1113 1088 1061 1060 i. ph.str. 999 1015 C-O-C o. ph.str. O-C-C-O 935 896 885 859 872

862 o o 889 837 835 839 Ar. 2adj. i. ph.str. O-C-C-O OH wag 793 H wag 789 768 OH wag

Para Quad. 708 677 679 i. pl.bend 697 646 640 643 638 617 604 604 CC wag 559 530 533 549 OH 507

493 HH CH

453 O

2 416 410 OH C H O O 22 23 24 O C 338 H O O

266 271 147 224 Glycolic acid 4-Hydroxy benzaldehyde Maleic anhydride 148 8. ILLUSTRATED IR AND RAMAN SPECTRA DEMONSTRATING IMPORTANT FUNCTIONAL GROUPS

CH wag 100 2 25 OH str. 80 548 688 1099

IR 891

60 1348 %T 1188 941 720 CH rk 1229 2 2676 40 1431 … … CH3 C=O 1295 Dimer O H O O 2955 o. ph. str. 1472 o. pl. wag 20 CH2 o. ph. str. CH3 (CH2)14 C OH CH2 i. ph. str. in dimer C-O str. 2849 1703

o. ph. str. 2918

CH2 CH2

0.8 2882 Trans chain bend twist Trans chain C-C-C i. ph. str. Palmitic acid

0.6 CH2 o. ph. str. 2846 Trans chain Ra C=O 1296 C-C-C o. ph. str. 1438 0.4 1063

i. ph. str. 1129 I 2924 in dimer 1422 1462 893 375 1099 0.2 2959 2725 671 1175 1634 0.0 100 OH str. 26 80 H H 723 IR 938 CC 60 2674 1247 1413 %T 1285 1462

=CH str. 3005 Dimer CH rk Cis CH wag 40 … … 2 C-O str. O H O o. pl. wag

20 CH 2855 CH 2 CH2 chain 2 o. ph. str. bend 2926 i. ph. str. 0.5 1711 O 2854

2898 C=O 0.4 CH2 twist Oleic acid o. ph. str. C=C str. CH 3(CH2)7 (CH2)7 C OH in dimer CC

0.3 1441 Ra HH I 0.2 1656 1303 226 3007 1083 857 1267 972 0.1 1022 1119 724 2726 0.0

100 Ring semi. str. 5 adj Ar-H wag OH str. + + C=O wag 27 80 combination bands

IR 60

%T 1496 1027

40 805 550 1126 3071 1180 O Dimer 20 1582 3007 2834 2674 1454 2559

… … 665 O H O C 934 1292 1424 o. pl. wag OH 1687 1326 707 C=O o 5.0 OH C-O str. o. ph. str. Ring i. pl. o 1002 Benzoic acid Aryl CH str. in dimer 4.0 quad. str. bend o

Ra 3.0 796 C=O I 2.0

i. ph. str. 1603 3073 618 1028 421 in dimer 1290 1635 1180 1.0 1132 1443 0.0 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber(cm–1) AMIDES, UREAS AND RELATED COMPOUNDS 149

CH2 chain wag 100 28 H2O str. 80 H2O bend 1302

IR 1113 60 720 3429 %T 1622 1421 CH2 chain

CH 2957 3 i. ph. rk. 40 o. ph. str.

1470 CO i. ph. str. CH2 2 20 CH3(CH2)16CO2 Ca 1576 o. ph. str. 1542 2850

2917 CO2 o. ph. str. 2

0.40 CH2 CH2 chain

2881 i. ph. str. i. ph. twist CH chain CH bend 2

2 Stearic acid CH2 chain C-C-C i. ph. str. 0.30 2846 o. ph. str. CH2 chain Ra

1296 C-C-C o. ph. str.

0.20 1441 I 1063 1130 1461 0.10 1103 891 2724 937 1370 1569 1176 2610 959 0.00

100 + NH3 str. 29

80 + CH2 bend IR summation 60 %T bands 608

3383 ) 2122 CO2 1032 1112 40 698 o.ph. str. 911 503 + 893 1444 3008 2614

20 3169 2970 2895 NH3 o. ph. bend NH CH CO 1333

1412 3 2 2 Zwitterion 1611 1522 ( CH2 str. CO2 893 0.6 NH3 i.ph. N-C-C i. ph. str. cine 1325

i.ph. str. y

bend Gl

0.4 2972 + Ra NH3 str. 495 1410 1035 3007

I 1440 359 602 696 1139

0.2 1568 1109 1668 2904 1515 1631 2615 3143 0.0 100

CH3 30 80 o. ph. bend

IR 876 1048 60 826 %T 1007 1744

2820 NH2

40 1154

wag 467 587 O 1354 20 1466 C-C=O CH3 CNH2 bend 1647 1396 3355 3167 0.40 NH2 C=O CH3 NH2 O=C-N

C-N Acetamide = o. ph. str. str. i. ph. rock 878 bend NH2 str. 0.30 CH3 str. bend C-C-N NH2 bend i. ph. str. i. ph. str. Ra 583

0.20 1151 458

I 2934 1356 1405

0.10 1591 3159 1639 1006 1679 3353

0.00 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber(cm–1) 150

1,3-Dimethyl urea N-butyl methyl acrylamide Acrylamide %T %T %T Ra Ra Ra IR IR IR I I I .ILSRTDI N AA PCR EOSRTN MOTN UCINLGROUPS FUNCTIONAL IMPORTANT DEMONSTRATING SPECTRA RAMAN AND IR ILLUSTRATED 8. 0.00 0.04 0.08 0.12 100 100 100 0.0 0.4 0.8 1.2 0.0 0.2 0.4 0.6 20 40 60 80 20 40 60 80 20 40 60 80 NH str. 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 1591 o. ph. str. NH str. o. ph. i. ph. 2 x o. ph. NH =CH =CH

str. 3354 =CH str. 2 3346 3343 2X 1542 3334 str. 3310 2 2 2 x 1543 2 x 3297 3176 3162 3186 o. ph. str. 3104 3104 3066 3101 2945 CH 3050 3030 3033

2960 =CH str. 3039 2947 2938 2 x 1429 2 x 2904 3 3011 2876 2935 2813 2902 i. ph.str. 2811 2812 =CH i. ph. str. 2872 2737 CH 2 3 C=O str. C=O str. 2 x 961 2 x C=C str. 1922 C=O str. C=C str. Wavenumber(cm

1668 NH 1673 1681 1636 1670 2 bend str-bend + C-Nstr. NCN HH 1624 NH bend 1627 1628 1633 C-N-H 1589 1552 1591 1613 o. ph. str. C-C-N 1543 CH 1541 1473 bend =CH 1429 1453 2 1459 1423 1420 1411 bend

1404 1433 2 –1 1352 i.bend ph. ) (N) CH 1311 H 1301 =CH 1281 1269 rk CC 1284 NH 1237 1233 o. ph. str.

1178 1175 2 C-O-C 3 rk 1136

1119 H 1145

1064 1053 1049 wag wag =CH NH wag 1043 1087 988 986 H CH 960 949 961 932 2 932 CC 959 2 873 =CH 871 833 845 841 o. ph. str. i. ph.str. CH 775 H 808

wag 810 N-C-N NH wag 2 C-C-N NH wag C

H 702 C=O 2

675 705 wag C O C wag H 3 665 620 616 H H N N HH 2 CC CH O C 505 511 509 H O(C H N O C CH 31 32 33 4 306 NH H 3 9 2 240 ) AMIDES, UREAS AND RELATED COMPOUNDS 151

…. 100 N-H O NH2 34 str. 80

IR 685 869 582 60 1283 994 1169 417 %T 635 2865 Ring N 793 H2N N O

40 2661 i. ph. radial NN 1447 1412 H 3464 1684 N O 20 3089 3185 NH NN 2 1719 1514 1615

0.6 698

Ring quad str. 389

“free” 580 C=O str. NON N-H str. H-bonded + NH2 bend Ammeline 235 NN 0.4 NH2 str. Ra

994 N 428 555 I 1617

0.2 653 1445 1548 1707 864 3459 1668 3186 1175 3059 1278 2878 0.0 100 35 80 2543 1136 3429 940

IR 2967 1277 60 1056 %T O 483 40 CH H3C 3 1391 N N 750 424 anurate 20 y OON C=O o. ph. str. 1477 CH3 1678 l isoc 0.8 CH y CH 3 579 3 1751 Ring C-N str. i. ph. bend 484 i. ph. str. C=O 700 0.6 + CH3 o. ph. i. ph. str. bend Ra Trimeth 0.4 I 2965 1387

0.2 1460 940 752 3007 1279 1136 1685 0.0

100 CH2 bend 36 80 NH wag

IR 991 60

%T 1038 3005 1105 1576

40 511 O H H 2957 2902 N C N 770 H C H CH 20 2 1451 N-C-N N N 698 1510 i. ph. str. 1675 o. ph. str. 1275 3308 1.6 CH2 C=O str. H H 934 N-H str. o. ph. str. N C N 5 membered ring 2-Imidazolidone 1.2 NH bend i. ph. str. + C-N str. Ra 0.8 I 999 1043 710 1518 2905 1659

0.4 1204 2964 498 1379 1109 1488 3304 0.0

3500 3000 2500 2000 1800 1600 1400 1200 1000 800 400 600 Wavenumber(cm–1) 152

Acetohydroxamic acid Ethyl carbamate Dimethyl formamide %T %T %T Ra Ra Ra IR IR IR I I I .ILSRTDI N AA PCR EOSRTN MOTN UCINLGROUPS FUNCTIONAL IMPORTANT DEMONSTRATING SPECTRA RAMAN AND IR ILLUSTRATED 8. 0.00 0.10 0.20 0.30 0.00 0.10 0.20 0.30 0.00 0.04 0.08 0.12 0.16 100 100 100 20 40 60 80 20 40 60 80 20 40 60 80 o. ph. NH str. 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 NH str. 2 2 X 1676 2 X

i. ph. 3422 NH 3407 str. o. ph. str. 3337 3336 2 3202 CH 3207 3206 o. ph. str. 3214 o. ph. str. OH str. OH 3 3040 CH 2996 2983 CH 2986

2944 2937 3 2931 3 2930 2916 2861 2870 2902 2936 2860 i. ph.str. CH (=O)str. i. ph.str. CH CH 3 3 C=O str. 1926 C=O str. Wavenumber(cm C=O str. str/bend bend

NH 1701 CNH 1690 1662 1676

1620 1623 1625 2 1616 CH

1566 (N)CH

1522 C-N str. o. ph. 2 bend CH 1484 1487 1500 1503 1460 CH 1438 3 1450 1427 1441 1439 3 1443 3 1408 bend 1390 bend –1 i.bend ph. 1378 1382 1388 1346 NH ) 1321 () CH O CO 2 1275 CH plbend i.

rk 1342 1257 3 1192 str 1131 i. ph.str. 1090 1093 NC 1086 1080 1128 1077 1093

1040 3 993 993 998 996 C-N-O str. 964 964 O-CH

OH wag OH 857 865 NH 858 2 867 752 str 792 2

679 NH C C 647 641 674 COCH O

C 658 H H 626 2 659 wag H 588 590 3 3 3 513 522 NC bend O C

449 444 O 2 405 CO N 355 CH N 37 38 39

349 H OH H 397 319 309

273 3 225 226 %T %T %T Ra Ra Ra IR IR IR I I I 0.00 0.10 0.20 0.30 0.40 0.50 0.00 0.04 0.08 0.12 100 100 100 0.0 0.2 0.4 20 40 60 80 20 40 60 80 20 40 60 80 OH str. OH 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 OH str. OH OH str. OH 3368 3376 3347 3366 3350 o. ph. str. o. ph. str. CH o. ph. str. CH 3 CH 2976

2972 2972 3 2977 3 2945 2945 2920 2924 2933 2882 2833 2883 2885 2714 2722 i. ph.str. 2837 CH

2567 i. ph.str. i. ph.str. 3 CH CH 3 3 o. ph. bend ALCOHOLS Wavenumber(cm o. ph. bend CH CH i.bend ph. 3 3

CH 1659 3 CH o. ph. bend 3 CH

1472 1466 bend OH-CH 1458

bend 1450 1455 1454 i. ph. CH bend CO bend 3 1383 1409

–1 1421 1365 3 1380 ) 1343

1310 H o. ph. str. + CH 1237 CH 1209 1200 C-C-O 1159 3 C

1152 rk 1132 3 1128 3

rk 1115 - 1103 C -

O str. 1023 953 953 1036 916 914 1030

818 C-O str. 749 820 C C 752 i. ph. str. CH C CH 655 664

642 C C C C CH CH O 3 3 O O O CH O H i. ph.str. 3 3 H 491 H wag 474 wag

wag 438 CH C CH

430 OH 40 OH 41 42 3 3

348 OH

t-Butyl alcohol Isopropyl alcohol Methanol 153 154 Phenol 1-Hexadecanol 1-Butanol %T %T %T Ra Ra Ra IR IR IR I I I 0.00 0.08 0.16 0.24 0.00 0.04 0.08 0.12 100 100 100 .ILSRTDI N AA PCR EOSRTN MOTN UCINLGROUPS FUNCTIONAL IMPORTANT DEMONSTRATING SPECTRA RAMAN AND IR ILLUSTRATED 8. 12 20 40 60 80 20 40 60 80 20 40 60 80 0 4 8 o. ph. str. CH OH str. OH 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 o. ph. str. 3 o. ph. str. CH CH OH str. OH str. OH 3331 2 2 Aryl CHstr. 3258 3303 3231 2956 3060 2918 2938 2959 3048 2881 2934 2846 2850 2724 2737 2877 2872 2638 i. ph.str. CH CH 2 2 i. ph. str.

2051 1934

Wavenumber(cm 1846 Quad str. Ar. Ring

1773 CH CH

1709 3 o. ph. bend

1597 2 o. ph. bend 1598 bend, circle str CH Semi- 1499 1501 Ar. 1473 1459 2 C-O-H –1 1462 1474 bend 1451 1437 1463 i. ph.str. ) i. ph. twisti. ph. C-O-H C-O str. 1408 CH 1369 bend 1379 Aryl 1370 (CH

3 1340

1296 str. C-C-C i.ph 1298 1300 2 Trans chain Trans 1254 1238 )

1254 n 1215 1169 1169 O 1130 1123 1114 1113 C-C-C-O i. ph.str. CH wag 1070 1063 1070 1070 1070 5 adj 1026 o. ph. str. C-CC-O Ar. 1024 996 1030 1043 o. ph. str.

980 str. ph C-C-C o. 964 C-C-O 953

1001 chain Trans 935 891 901 885 878 880 828 847 814 O O 811 811

754 H 720 O 738 CH wag crystal splitting 691 H CH 656 CH i. ph.rock 620 618 3 3 wag 2 O (CH 536 534 chain (CH 515 487

503 2 ) 15 2 )

398 3 43 44 45 OH OH 355 OH

245 ALCOHOLS AND ETHERS 155

100 46

80 1854 1798 1645 1912 1695 1584 588 880 449 843 3083 60 1094 3 adj IR 795 H wag 1391 1481 1362 40 2874 %T 1315 OH 1143 1171 (CH3)3C C(CH 3)3 20 2914 Ring 747

Quad. str. 1231 3644 Aryl-O str. 1426 2959

CH Ring 3 623 Free T-Butyl CH3 12 o. ph. str. semi- i. ph. bend OH str. circle. str. Aryl

CH str. CH3 o. ph. bend 8 2,6-Di- t -butyl phenol 291 Ra 845 2959 1198 326

I 2914 932 1471

4 528 3081 808 1096 1586 1272 1116 1231 447 747 1020 3639 0 100 H 47 CO 80 OH str bend H2O 1657 IR 60 (impurity)

%T 812

40 649 922 1236 1423 1354 1456 20 CH 896 2875 2 CH C-O-C C-C-O(H) i. ph. str. 2 2930 o. ph. str. o. ph. str. 1062

bend 1131 3370 0.6 CH2 354 2875 2936 896 o. ph. str. 1463 824 1081 0.4 1279 392 HO (CH ) O(CH) OH Diethylene glycol 1059 Ra 2 2 2 2 529 1119

I 1241 0.2 3349 2704

0.0

100 48

80 2734 839 739 1302 962 1234 60 1041 2796 1375

IR 1464 nC H O nC H %T 40 4 9 4 9

CH3 20 CH3 2960 2864 CH2 bend + C-O-C CH2 i. ph. o. ph. str. CH3 o. ph. bend o. ph. str. i. ph. str. l ether bend 1124 2935 y

CH2 1.2 2913 2872 o. ph. str. CH2 i. ph. twist 2938 n -Dibut 0.8 839 1449 Ra 291 1300 2797 960 879 0.4 1117 1484 I 1058 2735 0.0

3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber (cm–1) 156 8. ILLUSTRATED IR AND RAMAN SPECTRA DEMONSTRATING IMPORTANT FUNCTIONAL GROUPS

100 49

80 787 1971 577 656 2682 1290 1365

60 1461 IR 1183 %T 40 O C-O-C

o. ph. str. 912 20 5 membered ring i. ph. str. 2861 2975 1071

CH2 CH 0.3 2 CH o. ph. str. i. ph. str. 2 914 bend. Tetrahydrofuran 0.2 2962 2875 Ra I 0.1 1029 1486 1450 1232 1070 2719 2657 0.0

100 50 80 IR

1518 O 1193 %T 60 1092 2926 Cl CH2 CH CH2 1481 1137 3063

40 2964 Ring 1398 CH2

20 3003

Ring 1433 o. ph. str. 962 C-Cl str. CH2 bend 1267 927 724 855 Ring 761 CH2-(Cl) CH2 CH2-Cl

wag 374 Ring i. ph. str. CH -Cl bend 723 0.2 2 CH wag Ring o. ph. str. 2 1255 Ring o. ph. str. Ra i. ph. str. Epichlorohydrin

I 2965 1398 0.1 3007 443 223 1092 844 962 1137 2927 1479 1433 516 1206 3066 0.0

2 x 1618 100 51 80 2737

IR 1279 3377 3300 1616 %T 60 940 1065 1388 NH2 778 840

o. ph. str. NH2 1469 CH3 40 bend i. ph. bend CH3 NH 2872 NH 2 CH 2 20 i. ph. str. 3 C-N str. wag CH CH2 NH2 CH2 bend + i. ph. str. CH3

2956 CH3 o. ph. bend C 483 798 2931 C C 2870 2957 C 0.12 i. ph. 1458

Isobutyl amine str. Ra 362 I 0.08 280 1063 953 3329 1132 1173 1338 0.04 2719 3382

0.00

3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber (cm–1) AMINES AND AMINE SALTS 157

100 2 x 1621 52 80 NH2 wag NH 2 1840 IR 60 1929

%T 3071 993 1027 3214 40 881 3034 1467

20 3433 5 adj. 1175 H wag 691 501 3356 1602 1499 1622 1277 753

O 0.8 NH Aryl O 2 Ring 998 NH2 bend O o. ph. CH str. Semi- Aniline NH2 Ring 0.6 str. i. ph. Quad. str. circle str. Ar-N

str. 1029 Ra str. 816 I 0.4 3053 1604 533 622 0.2 235 390 1280 1156 1174 757 3356 3209 0.0 100 53 80 3287 961 1234 IR 60 1302 %T

1378 CH3 2810

40 735 CH3 i. ph.

o. ph. bend 1132 CH2 (N)

20 2870 str. i. ph. str. CH2 bend + 1462 NH CH o. ph. bend C-N-C wag 2958 3 o. ph. str. 2929 CH 1.6 CH 2 2 i. ph. Chain NH o. ph. C4H9 NH C4H9 str. CH twist str. 2934 2 1.2 str. 2875 1445 278 n -Dibutyl amine 2964 Ra 0.8 1298 834 2810

I 878 447 1058 896 0.4 1132 2735 1027 3327

0.0

100 54 80 732 IR 1690 2680 901 1251 940

%T 1304 60 1180 1377 2798 40 1086 C4H9 C4H9

1464 N CH CH2 (N) 3 CH3 20 o. ph. 2863 i. ph. str. i. ph. C-N str. C H 4 9 l amine str. CH2 bend + bend y 2957 2933 CH o. ph. bend CH2 3 CH2 i. ph. 0.20 o. ph. str. Chain str.

2874 CH twist

2934 2 Ra 0.15 n -Tribut

I 1445 2960 0.10 267 881 828 1301 903 1109 2799 1050 2734

0.05 947 1380 1179 1645 0.00

3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber (cm–1) 158 8. ILLUSTRATED IR AND RAMAN SPECTRA DEMONSTRATING IMPORTANT FUNCTIONAL GROUPS

100 55 80 2054 1732 818 2139 3419 1167 1371 466 IR 60 1067 %T

NC3 40 1414 CH3 1260 2960 i. ph. 3012 str. CH NHCl

2480 3 1485 20 2701 (N) CH NC (N) CH 2629 3 3 3 989 o. ph. o. ph. CH3 i. ph. str. bend str.

(N) CH3 NH str. (N) CH3 CH3 rk o. ph. (+ summation bands) i. ph. 819 3012 0.2 str. bend 990

Ra 468 2947 410 I Trimethyl amine HCl 0.1 1464 2875 1435 2471 2599 1071 2817 1404 1243

0.0 100 56 80 1753 1832 1071 1298 2347 457 3478 3094 2573 2469 IR 60 3397

2919 CH

%T 2952 3 40 1406 CH3 NCH3 Cl

3018 (N) CH 20 3 CH3 (N) CH3 (N) CH3 i. ph. o. ph. str. i. ph. str. 1492 CH rk bend 3 951

(N) CH3 758 1.2 o. ph. 948 NC4 3018 bend i. ph. 1481 457

2950 str. Ra 0. 8 I 2 x 1401 387 1454 1287 1401

0. 4 2878 1181 2787 Tetramethyl ammonium chloride 1529

0.0 100 2 x 700 wag NH o. pl. wag 2 57 80

NH2 str. 1807

IR 927 839 60 1028 1175 %T 2361 522

1110 5 adj. Ring o. pl. 1296 785

40 610 1368 2758 3420 H wag sextant bend 1446 1605

NCN 1526 20 o. ph. str. Ring 1482

Semicircle str. 691 3236 3063 O 1676 Ring O Quad str.

1.6 NCN 1003 i. ph. str. Benzamidine HCl Ra 1.2 Aryl CH str. NH2 765 I 1607 C Cl 0.8 394 1168 617 1531 1483 NH2 1032 3065

0.4 1097 692 3178 0.0 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber(cm–1) %T IR Ra Ra %T %T I IR IR Ra I I 100 100 100 1.2 1.6 0.0 0.4 0.8 0.2 0.4 0.6 0.0 0.0 0.1 0.2 0.3 20 40 60 80 20 40 60 80 20 40 60 80 o. ph. 2 x 1644 2 x NH str. o. ph. str 5030 5020 8010 4010 0080600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 NH str. CH 2 3492 2 x 1604 2 x

3490 i. ph. NH 3 3396 3397 3367 str. 3372 O-H 2 str. 3266 o. ph. str. o. ph. str 3181 CH 3163 2960 …. O-H

2963 CH 3088 3076 N 3 2965 str. 2983 2 2934 …. 2941 2926 2886 N 2943 2886

2875 i. ph.str.

i. ph.str 2766 2726 2874 2726 2793 2770 CH CH C CH H 3 2 i. ph.str 3 3 2449 CH CH

3 2294 (C C 2 H ¼ C=N str. C=N str. 4 N N AND N )O N N=O 1821 str. s O Wavenumber (cm -trans 1644 1670 1665 1676 1657 ¼ 1646 COMPOUNDS O s 1647 bend NH 1605 -cis 1650 1604 1593 1587 2 bend CH

CH 1465 CH 1483 bend o. ph.

1468 2 1452 CH 3 1430 1432 1427 1421 3 o. ph. bend 2 1386 1387 1399 –1

bend + 1371 1362 1365 C-N str. = o. ph. str. ) 1337 1331 C-N-C bend i. ph. 1308 CH 1289 1237 1255 1252 3 bend i. ph. 1171 1169 1184 1184 CH 1136 1139 1117 3 1102 1063 N-O str C 1053 N-O str. 1045 1048 1016 C C 1021 974 983 982 957 C 942 902 921

i. ph.str. 917 911 N-O str. wag NH/OH 874 894 833 i. ph.str. 821 C-C-N 800 782 809 wag NH/OH 763 H 777 O 692 700 708 645 N 651 654 620 620 600 603 592 589 603 C H NNOH H 513 513 511 511 3 475

461 C 400

423 411 416 NOH

409 NH 413 358 58 59 60 352

337 2 297 303 265 250 Isoamyl nitrate Pipenidindione dioxime Acetamide oxime 159 160

Azo-tert-butane Isopropyl nitrate 2-nitropropane %T %T IR IR %T Ra Ra IR Ra .ILSRTDI N AA PCR EOSRTN MOTN UCINLGROUPS FUNCTIONAL IMPORTANT DEMONSTRATING SPECTRA RAMAN AND IR ILLUSTRATED 8. I I I 100 100 1.2 1.6 2.0 0.0 0.1 0.2 0.3 0.0 0.4 0.8 100 20 40 60 80 20 40 60 80 10 20 40 60 80 0 5 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 + NO + NO CH Isopropyl CH str

3229 Isopropyl CH str 3 2 2 str. str. combination 2974 str. combination 2976 2996 2994 2997 2996 2948 2944 2950 2923 2931 2874 2945 2874 2867 2877 2929 2887 2900 2735 2707 2742 (H 2551 3 C) 3 C N N o. ph. str. Wavenumber(cm C(CH NO N=N str. 2

1626 o. ph. str. o. ph. bend 3 ) NO 3 1624 o. ph. bend CH 1572 1551 2 1552 CH bend i. ph. 3

CH 1470 1477 NO 3 1450 1453 1450 1448 + CH 1468 3

t-Butyl CH t-Butyl 1390 i.bend ph. –1 NO 1385 1400 2 1400 i. ph. str. ) 1366 1362 1351 1378 3 2 1360 bend i. ph. str. 1305 1359 1277 1279 1306 1240 1241

1207 3 1211 1183 1183 o. ph. str. (C) Involves 1179 1179

1146 N-O str. 1144

3 1101 1102 1102 1102 C-N 1027 1026 1037 C 941 953 C i. ph.str.

928 Involves N-C(C) 908

i. p.str. 908 868 880 902 C 842 851 N C

C 853 796 i. ph.str. 852 851 3 C 760 715 715 706 721 C O

CH 706 H N 3 C 3 594 620 C 621 H H C-N=N bend + C-N=N bend 561

553 CH 562 3 544 3 525

Involves 524

503 C-C str.

459 NO CH 409 ONO 364

333 62 63 318 61 2 263 257 2 BORONIC ACID, CHLORINE AND BROMINE COMPOUNDS 161

100 B-OH wag 64 80 841 492 917 765 652 592 IR 788 60 1121 1582 Nujol 1224 1604 %T 3032 ) 1181 1199 1042

3 adj 708 1311

40 1456 3266 H wag

Involves 727

20 Aryl Ring 1419 B-OH bend

2854 Quad Str. OH str. 1001 2924 1348 226 lboronic acid H3C

Aryl y CH str. O Ra OH Involves I 10 O-B-O str. Aryl B O lphen 702 y

CH str. 1605 3 OH 528 meta -tolyl boronic acid 1583 381 801 335 3060 1379 827 665 3-Meth 584 1346 505 ( 2918 1202 1414 1168 1089 3036 1045 1310 2865 3206 0

100 65

80 915 1377 IR Cl(CH2)7 CH3 1306 60 (Cl) CH wag 654 %T 2 725

40 1462 CH CH 3 H 3 i. ph. C-Cl str. C-Cl str. o. ph. Cl 20 bend C

2958 2857 C trans H trans to Cl str. CH2 bend + CH2 to Cl CH3 o. ph. bend

2928 i. ph. str. CH2 o. ph. C 656 0. 8 2936 str. 2874 CH2

2857 Cl i. ph. twist H 0. 6 2958 246 1-Chlorooctane Ra 1445 I CH2 (Cl) 0. 4 730 o. ph. 1304 457 1080 846 893

str. 1119 1039 2996 1170 0. 2 2731

0. 0

100 66

80 953 852 Br (CH2)5 CH3 1047 726 646 564 1379

IR 3003 60 1279 %T 1204

1241 CH2

40 1465 i. ph. rk

CH (Br) 2859 H 2 (Br) CH wag o. ph. CH 2 Br 20 3 C C-Br str str. i. ph. 2959 H trans CH2 C-Br str i. ph. str. bend C trans to Br to Br 2930 0.16 C CH3 CH bend + CH 2 Br o. ph. 2 CH o. ph. bend H 565 o. ph. str. 3 CH 0.12 str. 2 1-Bromohexane 2936 i. ph. twist 646

Ra 2963 2875

I 0.08 249 1440 380 485 1306 1067 754 0.04 801 3011 1111 962 2732

0.00 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber (cm–1) 162 8. ILLUSTRATED IR AND RAMAN SPECTRA DEMONSTRATING IMPORTANT FUNCTIONAL GROUPS

100 67 80 2867 1004 1382 3040 1079 887 1518 2924 IR 60 528 728

%T 857 444 40 1460 Aryl CH3 925 1251 1590 20 i. ph. bd. 682 H3C F Lone Aryl 1620 1004 729 H wag 777 1265 1142 CH str. 1489

Involves 3 adj Aryl Ring Aryl CH str. Ar-F str. H wag 20 3 Quad Str. 245 Ring O 528 3-Fluorotoluene Ra semi-circle I 10 O 514 3061 1265 2924 1251 3080 1620 1079 1381 557 1142 1160 2870 1596 1446 1490 0 100 68 80 1936 IR 1862 2861 1384 %T 1042 998 1164 60 3063 2924 1100

Lone 434

40 1217 H wag 1577

20 1603 Aryl CH3 1078 H3C Cl i. ph. bend 999 856 1477 682 773 Aryl Ring Involves 3 adj CH str. semi-circle Ar-Cl str. H wag Aryl CH str. Ra 20 3 Aryl Ring I Quad Str. O 684 416 3-Chlorotoluene 236 521

O 10 3064 1079 2924 1217 388 856 1602 1577 1165 1383 1099 2862 1452 0 100 69 80 1936 2859 1040 1381

IR 3061 1165 60 869 2922 %T 995 1452 1212 40 429 Lone 667 H wag 1601 20 1569 308

Aryl CH 1071 H3C Br 3 681 1473 i. ph. bend 834 770

30 Ring 996 Aryl 3 adj semi-circle Involves H wag CH str. Aryl Ring Ar-Br str. O

3-Bromotoluene Quad Str. Ra 20 Aryl CH str. 3 667 I O 522 10 1071 3061 2922 834 1212 1601 1570 1380 1165 1028 1093 2861 1450 0 3500 0300 2500 2000 1800 1600 1400 1200 1000 800 600 400

Wavenumber (cm–1) SULFUR COMPOUNDS 163

100 70 80 2094 1996 2336 900 2822 1659 669 60 2911 IR 1311 3442 700 2995 %T H2O 1408 955 40 bend 1437 C-S-C H O (S) CH3 2 (S) CH i. ph. str. 20 OH str. 3 i. ph. i. ph. str. (S) CH3 bend rock 1053

(S) CH 670 3 (S) CH C-S-C 0.6 o. ph. str. 3 S=O str. O o. ph. o. ph. str.

2914 bend 0.4 CH S CH Ra 3 3 Dimethyl sulfoxide I 335 0.2 699 307 2998 384 1045 1421

0.0 954 2819

100 71 80 908 2258 1435 60 984 1415 IR 2940 3018 %T CH3 SO3 Na 1337 40 (S) CH 3 790 20 (S) CH i. ph. SO 564 3 3 C-S 1249 i. ph. str. bend i. ph. 535 str. 1062 str. 1220 1184 SO3 (S) CH bend. 0.6 3 799 o. ph. str. (S) CH3 1078 SO3 o. ph. 577 o. ph. str. bend 353 0.4 2940 Ra 544

I 1052 3021

0.2 1453 1412 1204 1170 968 Methane sulfonic acid, sodium salt

0.0 100 H O+ str. CH o. ph. bend 3 3 - SO3 72 80 o. ph. str.

IR 60 drate 846 y 1401 493 706 %T 1495 1455 1597

40 1659 2930 677 1850 816

2670 2243 Ring SO - 20 semi-circle 566 3 Aryl 2 adj. bend 1007 str. 1037 1181

1124 - H wag SO3 Aryl CH str. Ring Aryl-S i. ph. str. + O 0.4 (aryl) CH 801 3 Quad. str. p-aryl ring 1126 i. ph. str. mode

0.3 818 O 234 Ra 3066 270 1599 I 0.2 635

CH SO H O 1045

3 3 3 316 396 1188 2932 1379 1215 680 1014 0.1 1454 553 703 para -Toluene sulfonic acid h 2986 (Sulfonic acid Hydrate) 1308 0.0

3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber (cm–1) 164

Zinc dimethyl dithiocarbamate Sodium isopropyl xanthate Dodecyl sulfate, sodium salt %T %T IR IR Ra Ra %T .ILSRTDI N AA PCR EOSRTN MOTN UCINLGROUPS FUNCTIONAL IMPORTANT DEMONSTRATING SPECTRA RAMAN AND IR ILLUSTRATED 8. I I IR Ra I 100 100 0.0 0.2 0.4 0.6 0.8 100 0.0 0.0 0.1 0.2 0.3 0.4 0.1 0.2 0.3 20 40 60 80 20 40 60 80 20 40 60 80 o. ph. str. CH 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 H str. H str.

3503 2 H 2 O 3 str. H O str. 3435 2 3458 O 2

3381 o. ph. 3349 O CH str. o. ph. str.

3203 2 o. ph. str. CH

CH 2978 3013 2954 2881 2955 2936 3 2976 2929 3 2928 2873 2929 2918 2859 2857 2872 2850 CH 2800 2731 CH 2729 2848 3 3 CH i. ph. CH CH str. 3

2358 (CH CH 2 CH OC 3 2 3 ) NC 2091 2107 11 S S H OSO - 2 S S

1935 O Na xH bend H 2 bend H 2 O CH C-N str.+ Zn 2 3 O bend H Wavenumber (cm Na 3 2 CH CH O bend 2 2 bend 3

O 1658

1630 bend + 1625 1627 o. ph. 1609 o. ph. bend

1522 CH o. ph. str. 1512 1459 3

1463 SO

1454 i. ph. twist 1445 1448 CH 1468 o. ph. str. bend bend i. ph. 1439 i. ph. 1442 1437 CH CH 3 C-O-C –1 1391 2 1392 1371 1379 ) 1373 3 1345 3 1320 1297 C-C-C CH bend

1327 ph. i. chain o. ph. str. 1245 1244 str. 1250 C-C-C

1189 1189 CH 1221 1168 i. ph. ph. i. 3 1146 SO 1150 1149 1140 1140 1130 str. rk 1104 o. ph. str. 1086 o. ph. str. 1089 3 1085 1049 1052 CS

CS 1064 o. ph. S-O-C 979 o. ph. str. 2 1037 993 992 str. C-C-C chain 965 2 974 943

885 907 i. ph.str. 905 891 920 O-CC 838 836 815 812 i. ph. rk. ph. i.

i. ph.str. 763 2 i. ph.str. S-O-C CH CS 722 i. ph.str.

664 2 hindered rotation 669 2 637 CS 635 608 599 H 2

bend 592 567 SO

2 575 571 507 O wag 3 438 422 445 393 465 449 371 CCC i.pl. 407 73 364 C-O-C, bend 74 299 75 292 223 %T %T %T IR IR IR Ra Ra Ra I I I 100 100 100 0.0 0.4 0.8 1.2 1.6 0.0 0.4 0.8 1.2 1.6 2.0 1.0 2.0 3.0 4.0 80 40 80 20 60 0.0 20 60 20 40 60 40 80 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 o. ph. NH str. CH str.

o. ph. 3461 3443 3 CH str.

Aryl CHstr. 3285 2

o. ph. 3249

3245 CH str. 2960

3063 2 2936 3049 2910 2966 ph. i.

3001 CH

str. 2961 2936 2894 2885 2874 2 2737 2875 2735 2574 i. ph.str. H

2426 COMPOUNDS PHOSPHORUS AND SULFUR CH 3 (CH 2 2 ) 3 O(CH summation bands 3 P Phenyl CHwag 1958 O P

O 1888 (CH

1815 NCN HH Wavenumber (cm + CNstr. NH bend 2 )

3 1768 CH Quad. Str. 2

) 1714 3 CH 3 Ring 1667 3 CH CH 1584 1582 2 bend 1521

3 1571

1520 CH bend + o. ph. Semi- circle Ring 1476 1483 1464 str. 1450 1467 1500 1465 2 1435 bend -1 ) N

bend 1378 1381 i. ph. 1381

CH 1372 2 P-phenyl str. 1308 1310 C=S str 1310

1300 3 1284 1262 1264 1281 1277 CH O P-O-C o. ph. str. 1212 + C 1178 1232 1178 1207 2 1148 1158 twist 4 1120 str. O chain 1062 1095 1090 1109 1064 1023 1028 1050 1047 1036 1024 1001 1002 996 979

967 H wag 964 1000 5 adj. 906 914 923 878 920

884 str. ph. ring i. membered 5 833 ph. str. i. + P-O-C 853

PO 743 817 O i. ph.str. 774 3

772 PO 721 718 o. ph. str. 683 665 681 3 697 619 592 545 552 H

500 O 509 492 N 510 C 409 S N

330 76 77 78

272 H 252 213 Tributyl phosphite Triphenyl phosphine 2-Imidazolidinethione 165 166 8. ILLUSTRATED IR AND RAMAN SPECTRA DEMONSTRATING IMPORTANT FUNCTIONAL GROUPS

100 79 80 1640 3478

H O 732

2 832 901 795 2425 1383 bend 1150 IR 60 554

1464 O %T H2O str. 40 CH CH3(CH2)3 O(CHP O 2)3CH3

2876 3 i. ph. H CH3 1069

20 i. ph. bend 1033 CH3 P-O-C o. ph. str. 1261 2962 o. ph. str. str. + PH wag 976 2.0 2913 . P-H str. CH2 bend + P=O str. PO2 P

2875 CH o. ph. 1.6 3 i. ph. str. O O 2937 bend CH2 twist 1.2 832 Ra 2963 n -Dibutyl phosphite 775 I 1453

0.8 294 1302 1259 886 395 907 1121 720 1063 475 2430 958 2734 1150 0.4 1391

0.0

100 80

IR 80 2087 2725 1263 1161 %T H O 1130

2 468 1621

bend 1368 60 1392 910 570 3409 40 2875

1468 CH 841 812 3 950 i. ph. PS2 CH3 CH2 bend + 20 H O str. 686 i. ph. str. 2 i. ph. CH o. ph. bend P-O-C

2960 3 CH3 o. ph. str.

str. bend 994 o. ph. 2.4 PS2 417 str. 282 o. ph. 564 2875 P-O-C 2.0 (CH ) CH CH O

str. 455 3 2 2 S i. ph. str. Ra 830 2963 2901 P Na - 1464 I 1.6 (CH ) CH CH O S 319

3 2 2 523 1.2 367 965 797 1343 0.8 1130 1301 1260 1179 H O 995

2 1372 926 2723 3374 0.4 bend 1632 Sodium di-isobutyl dithiophosphate 0.0 100 81 1721 2851 662

80 1945 1604 1445 1385 2906 1412 702

IR 687 %T 60 864

40 Si CH3 Si CH3 2963 o. ph def. 20 o. ph str. Si CH3 i. ph str. 1261 800

0 1092 1020 491 2907 Si CH rk 1.6 CH3 CH3 Si-O-Si 3 o. ph. str. 1.2 O Si O Si Si CH3 i. ph def. 710 2966 Ra 0.8 CH CH I 3 3 688 790

0.4 1413 867 1265 2809 3114 0.0 Siloxane polymer (silicone grease) 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 INORGANIC COMPOUNDS 167

100 H O bend 2 82 H2O str.

80 671 2004 IR 60 1647

%T 1755 40 H H N H Cl 20 2806 2 x 1402 H 1402 3042 3136 NH4 1.2 i. ph. NH NH bend 4 str. 4 o. ph. str. 3047

0.8 Ammonium chloride Ra 2 x 1405 I 3140 474 1405

0.4 2822 1759 2006

0.0

100 83 80 2096 1622 IR 3434 60 %T H2O H O str. 40 2 bend 639 SO4 617 20 i. ph. str. 1130 SO 4 SO 3.0 994 4 SO o. ph. 4 bend i. ph. o. ph. bend Sodium sulfate str. Ra 2.0 SO4 2 Na I 1.0 633 466 621 1132 451 648 1101 1153 0.0

100 496 + 970 632 84 80 + 496 1622 1931 IR 3435 %T 60 2 x 970 1435 1214

H2O H O str. 2 x 632 1137 40 2 bend 632 496 20 SO3 SO3 i. ph. + o. ph str. 970 o. ph. SO 2.0 3 bend 988 i. ph. SO3

SO Sodium sulfite 1.6 3 o. ph. bend i. ph. str. str. . 1.2 . Ra SO 2 Na 950 I 3 0.8 498

0.4 639 0.0 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber(cm–1) 168

Potassium nitrate Sodium bicarbonate Sodium carbonate %T %T IR IR %T Ra Ra Ra Ra IR .ILSRTDI N AA PCR EOSRTN MOTN UCINLGROUPS FUNCTIONAL IMPORTANT DEMONSTRATING SPECTRA RAMAN AND IR ILLUSTRATED 8. Ra Ra I I I 100 100 100 100 0.0 1.0 0.5 0.0 20 40 60 0.1 0.4 0.3 3.0 80 0.2 80 2.0 60 80 20 40 40 20 60 60 80 0 20 40 H 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 O H H str. str. 2 2 O 3435 O 3436 C CO

O 3431 O NO 3 2 Na 3 Na 2955 2 K 3070 2855

2741 2906 2919 + 1081 1442 + 1051 Hstr. OH

1385 2495 2398 2535 2545 + 702 2045 1081 + 716 1051 1913 1922 Wavenumber (cm 1845 1769 1778

1764 o. ph. str. CO 1684 1696 1621 2 1661 1615 H 1623 1618 o. ph. str. H 2 2 O bend O bend CO o. ph. str. 1457 1429 3 NO + OHdef. 1360 1437 o. ph. str. 1452 1442 O-CO

–1 1400 1345 3 1385 ) 1309 1268 2 i. ph.str. i. ph.str. i. ph.str. CO NO CO

1046 3 3 2 1046 1033 1081 1051 992 1000

o. pl. o. 880 bend o. pl. o. bend CO bend CO NO

bend 834 i. pl. 826 837 NO 3 2 3 bend i. pl. CO

716 3 698 686 702 695 696 3 660 657 647 567 86 85 87 226 205 %T %T %T IR IR IR Ra Ra Ra I I I 100 100 100 0.0 2.4 3.2 0.8 1.6 40 60 20 40 60 80 10 20 80 20 40 60 80 10 12 2 4 6 6 8 0 0 2 4 8 HO 5030 501800 2500 3000 3500 O H 3545 2 H OH str. H O P 3430 2 2 O 3311 3345 O O 3254 3217 O 3178 2 Na

2852 2853 2 -Hsr+ P-OHbend P-OH str 2631 H

O 2516 2454 2402

2362 O O OH B 2262 2279 NRAI COMPOUNDS INORGANIC 2000 2095 P

O 2031 O O H 3 Na

Wavenumber (cm 1790 1796 3 H 12 H 2 1600 1664 O P-OH bend 2 o. ph.str. 0 1566 BO

1400 1449 3 1392 1423 –1 1378 1384

) 1358 1359 o. ph.str. 1200 o. ph.str. PO

1194 PO 1165 1181

1156 4 i. ph.str. 1131 1072 3 BO 1000 1066 1073 1031 P-O(H) str. 1004 1013 3 999 936 993 Involves OH wag + BO 948 i. ph.str. 882 884 o. pl.bend

PO 938 800 861 860 811 816 i. ph.str. 3 PO 692 PO 4 600

BO 647 OH wag + 3 588 600 577 3 590 o. pl.bend 3 546 560 549

def. 547 551 500 505 524 400 462 462 399 416 88 90 89

209 234 Boric acid Dibasic sodium phosphate Tribasic sodium phosphate 169 170

Silica gel Sodium molybdate Sodium perchlorate %T IR %T %T Ra IR IR Ra Ra .ILSRTDI N AA PCR EOSRTN MOTN UCINLGROUPS FUNCTIONAL IMPORTANT DEMONSTRATING SPECTRA RAMAN AND IR ILLUSTRATED 8. I I I 100 100 100 120 100 0.0 0.4 0.8 1.2 1.6 20 40 60 80 20 40 60 80 20 40 60 80 20 40 60 80 20 40 60 80 0 0 3500 H H 2 NaClO

2 3536 O O

3453 H Si 3443 3438 2 3296 3305 O O O 3000 4 Na • H 2 x MoO 2 O • 2500 xH 4 2 O • H

2 2223 O 0010 6010 1200 1400 1600 1800 2000 2060

Wavenumber (cm 1970

1872 1801 H 2

O 1698 H H 2 2 O 1677 1636 O 1632

–1 1560 )

1402 o. ph. str. Si-O-Si o. ph. str. i. ph. str.

1183 ClO 1135 MoO 1149 1108 1092 4

1000 1098 1078 4 1089 1085 ClO 977 969 904 i. ph.str. o. ph. str. 953 941

899 4 896 858 MoO 891 800 843 o. ph. str. MoO 834 800 793 808834 822 4 o. pl. bend. 4

674 657 ClO 659 600 639 629 600 621 4 626 547 ClO 479 i. pl.bend. 400 468 483 445

399 4 91 93 92 324 285 %T %T %T IR IR IR Ra Ra Ra Ra Ra Ra I I I 100 100 100 0.0 0.0 0.0 1.0 2.0 3.0 4.0 1.0 2.0 1.0 2.0 3.0 4.0 5.0 80 90 20 40 60 80 50 60 70 80 90 H 3MgO 2 O (hydrate)

OH str OH 3675 5030 2500 3000 3500 3661 • o. ph str. 4SiO =CH str. CH 3 22 •

3073 H 3078 2953 2950 3006 3006 O (Talc) CH 2924 2904 2908 2915 2884 2 2917 2844 2844 2867 str 2840 o. ph str.

2723 i. phstr. 2838 CH CH 2 3 NRAISADPOLYMERS AND INORGANICS 2000 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 C=C str Wavenumber (cm 1668 1653

1655 1640 CH CH 3 o. ph. def CH 2

1447 def. 1438 2 1460 1455 def 1436 1436 CH def.

Trans CH wag CH Trans 1404

1360 i.def. ph. 1376 1312 1330 1359 1304 CH

–1 1304 3 ) 1277 1239 1219 1209 1152 1167

1077 1065 str. involves MgO/SiO 1079 1037 1051 1011 993 999 998 1015 964 973 973 944 911 899 899 842 *CH 841 i CH Cis 809 809 792 * wag 726 676 H

2 665 2 CCH CH Cis, Trans

529

CHCH 468

466 456 CH 432

399 3 96 95 94 2 362 321 171 N * N 291 * 251 Polybutadiene Isotactic polyethylene Talc 172

Polytetrafluoroethylene (Teflon) Polyethylene oxide Polyvinyl alcohol (PVA) %T %T %T IR Ra Ra Ra Ra IR IR Ra Ra .ILSRTDI N AA PCR EOSRTN MOTN UCINLGROUPS FUNCTIONAL IMPORTANT DEMONSTRATING SPECTRA RAMAN AND IR ILLUSTRATED 8. I I I 100 100 0.0 1.0 0.0 1.0 2.0 1.8 20 40 60 80 20 40 60 80 80 90 98 10 0 0 2 4 6 8 *CF 5030 502000 2500 3000 3500 OH str. OH

3386 2 o.ph.str. 3280 CF CH 2 2 CH 2937 2940 2946 CH str. 2

2885 str. 2880 2909 N 2906

* 2807 2695 2720 *CH *OCH 0010 6010 2010 0 0 400 600 800 1000 1200 1400 1600 1800 2000 2 2 OH CH CH 2 aeubr(cm Wavenumber N * N * 1710

1607 1568 Def. CH Def. CH OH def. 2 2 –1 1479 1467 ) 1447 1444 1419 1417 CH def. 1381 1396 1360 1370 CF 1341 1367 1295 1322 1299 2

1281 C-O-C Involves 1279 o. ph.str. Involves C-O str. 1202 1237 1241 1240 1238 1218 o. ph. str. 1147 1141 1145 1148 1142 1094 1087 1062 1093 1059 1028 1023 961 929 C-O-C Involves 947 915 916 858 844 i. ph.str. 841 856 841 CF

734 2 def. 637 620 599 626 582 575 536 483 421 99 97 387 363 98 290 279 231 POLYMERS AND BIOPOLYMERS 173

100 OH str. Involves 100 90 IR C-O str.

%T 2650

80 3032 2936 1377 1412 1452 904 607 70 CH2 o. ph. str. 1105 795

CH2 def. 1231 60 1167

5.0 2938 1697

4.0 1456 C=O str. *CH2 CH * Poly acrylic acid 819 Ra 3.0 316 607

I C 1102 506 1318 912 1339 2.0 O 1004 HO 1673 N 1182

1.0 1609 3069

0.0 100 90 101

80 933 895 3450

IR 2882 2949 1073 1017 844 733 %T 1492 1372 1315 70 1167 1460 1228 60 646

50 1421

1284 N-C=O bend 1270 40 1655 2925 CH2 def. 3.0 CH def

2977 C=O str. 1426 CH2 CH 934 756 Ra 2.0 1347 N 1456 1231 I Polyvinyl pyrrolidone O 852 554 364 1494 1671 1370 898 1023 606 1311 648 1076 1.0 1107 N

0.0

100 CNH str/bend NH wag

3429 102 3077

90 1043 936 1141 2859

IR 1180 2932 1371 %T 80 728 CH 1473 1200 2 1416 1464 3296 CH i. ph. str. 1274 2 687 o. ph. str. CH2 70 Involves NH str. def.

1535 CNH str/open 1631 2919

H H lon 6,6

*C(CH ) C N (CH ) N * y 3.0 C=O str. 2 4 2 6 1441 N

2867 O O N

2.0 1298 Ra I 1637 1063 1128 952 1235

1.0 1475 1382 3304 601 2732 1550 0.0 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber (cm–1) 174 8. ILLUSTRATED IR AND RAMAN SPECTRA DEMONSTRATING IMPORTANT FUNCTIONAL GROUPS

Involves C-O str. of COH/C-O-C 90 103 1642 IR 80 2939 1202 2894 1281 1427

%T 1369 898 70 1315 3274 3334 H2O 60 1160 663 50 CH2 def 1105

40 OH str. OH def 1054 1095 5.0 CH def 1030 379 OH Ring semi-circle str. Cellulose 4.0 1120 OH 437 Ra O HO * 457 3.0 O O 2895 HO O I 1379 OH 491 519 1149

2.0 1339 OH N 1294 897 1474 568 996 1.0 Cellulose 970 3381 252 2730 0.0 Involves C-O str. of 100 COH/C-O-C 104 IR 90

%T 1639 2927 1241

80 1410 1337 3309 856 761 70 H O 1148

2 706 OH def 927 60 1077 CH def OH str. 50 479 992 OH 5.0 Involves Ring in-phase and CH2 def C-O str of Semi-circle str. Starch 4.0 O OH COH/C-O-C Ra O HO I 3.0 O 441 OH 361

O 308 1123 1339 1085

HO 939 1380

2.0 864 578 1054 2908 OH * 1459

O 1262 717 Starch N 765 1.0 1211 3395 0.0

98 Involves C-O str. 105 of COH/C-O-C IR 2878 %T 3223 90 1266 904 1322 1413 699 1590 1100 OH str. CO2 CO 80 2 o.ph.str. i.ph.str. Ring semi-circle str. 1021 2.0 OR 1048 1115 RO * 2900 O 430 356 1374 O 477 1418

* 302 Ra 916 1328

I 1451 1.0 OR N 1263 579

R = H or CH2CO2

Sodium Carboxyl 700 1611 3392 Sodium carboxymethyl cellulose Methyl Cellulose Involves C-O str. 0.0 3500 3000 25002000 1800 1600 1400 1200 1000 800 600 400 Wavenumber (cm–1) %T %T %T IR IR IR Ra Ra Ra Ra I I I 100 0.0 1.0 2.0 100 0.0 0.0 20 40 60 80 1.0 2.0 3.0 4.0 5.0 1.0 2.0 100 80 90 60 70 80 90 OH str. OH 3500 of OCH o. ph. str. OH str. OH

o.ph. str. 3471 3438 3451 2 CH CH 3000 3 3

3113 CH 2965 2962 2975 2974 2967 2906 3 2932 2935 CH i.ph. str. str. 2904 2928 2899 2876 2871 2893 2815 2 2837 2836 (O) o. ph. str.

2500 2716 R = H or * * * R = H or O RO O RO OYESADBIOPOLYMERS AND POLYMERS O 2000 CH OR OR 3 CH CH Si or

1942 CH 3 3 O OR O OR 2 1800 CH O 3 CH Wavenumber (cm 2 N * N CH * Si CH CH O 3 3 H H H CH 1600 2 2 O O * 3

N 1636 1636

1593 CH CH o. ph. def. 2 Si CH def 2

1400 1486 1484 1458 def 1444 1455 1453 1411 1413 1403 CH def 3 –1 1371 1375 i. ph. def. 1369 1373 ) Si CH 1354 Involves C-O str.

1310 COH/C-O-C of 1313 1200 1263 1261 1270 Involves C-O str. 1280 1267 of COH/C-O-C 3 o. ph. str. 1203 1201 1191 Si-O-Si 1159 1152 1115 1101 1122 1100

00800 1000 1089 1029 1054 1030 1051 Ring in-phaseand

946 Ring in-phaseand 915 Semi-circle str. 917 944 Semi-circle str. 867 Si CH 882 882 891 842 854 rk 823 790 800 817 3 754 709 687 699 701 600 643

492 400 438 458 107 106

108 388 290 251 Siloxane polymer Ethyl cellulose Hydroxypropylmethyl cellulose 175 176 Poly-2-(acryloyloxy)-Ethyltrimethyl Ammonium Chloride (AETAC) Poly acrylamide (PAM) %T %T Ra Ra IR IR I I 0.00 0.10 0.20 0.30 0.00 0.10 0.15 0.20 100 0.05 20 40 60 80 100 .ILSRTDI N AA PCR EOSRTN MOTN UCINLGROUPS FUNCTIONAL IMPORTANT DEMONSTRATING SPECTRA RAMAN AND IR ILLUSTRATED 8. 20 40 60 80 4000 o. ph. str. ph. o. H NH 2 O OHstr. NH 2 3400 NH str. + 2 2 str.

3379 i. ph. str. 3359 3344 NH CH o.ph. str. o.ph. 3000 3208 3199 3022 2 3

3013 str. ph. o.

2970 (N 2932 CH + 2931 2960 2925 CH (C=O) )

2830 H H 3 3

C C 2858 o. ph. str. ph. o. 2 str. 5020 8010 4010 00806040200 400 600 800 1000 1200 1400 1600 1800 2000 2500 Cl CH N CH 3 C 2 2 H CH 4 O 2

C CH 2858 9 O C=O str. H CH 2 N 2 C CH C=O str. Ester O 1 Wavenumber(cm

1730 bend C=O str. NH

1733 Amide 1673 1663

1671 2 bend

1658 NH o. ph. bend ph. o.

CH 1610

2 1621 3 (N

1485 bend CH

1452 C-N str.

+ 1453 1456 1451 ) 1390 1424 2 1419 Involves Ester -1 1341 ) 1341 1325 CH rk 1349 1270 C-O str. 1256 1323

1210 NH 1144 1166 1177 2 NC 1084 1108 rock 1124 + CH

1039 4 1057 i. ph. str. ph. i. o.ph. str. o.ph.

953 999 C-C-N

3 955

874 rk 849 877 843 774 783

720 str. i.ph. H CH NC 2 NH N 2

4 639 2 wag 109 110 C CH 454 483

379 O CHAPTER 9

Unknown IR and Raman Spectra

On the following pages, 44 unknown spectra are presented without labels or interpretation to help test and develop the readers knowledge and understanding of functional group analysis and spectral band assignment. The spectra are found on pages 178 to 199. The sample preparation used to acquire the spectra is provided and where appropriate hints are included to help guide the interpretation. For interpretation and an explanation of the key features useful to help identify each compound an answer key is included at the end of the unknown spectra starting on page 200.

177 178 9. UNKNOWN IR AND RAMAN SPECTRA

100 3154 80 2612

1257 Neat/cap film 2793 903 862 2660

IR %T 40 1450 20 1 2852 2917 801 5.0

4.0 Ra I 3.0 2852 2938 2.0 1028 1266 1.0 1444 426 1157 384 1347 2665 0.0

100 811 984 919

80 3182 2720 1168 60 Neat/cap film 2840 1367 IR 40 1386 %T 1468 20

2871 2

0 2903 2957 809 8.0 2873

6.0 2959 Ra I 4.0 469 306 1464 1452 2.0 956 921 1346 1158 1320 2719 420 249 1252 870 1036 0.0

3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber(cm–1) %T IR %T Ra IR Ra I I 100 100 0.0 2.0 4.0 6.0 10 15 20 40 60 80 20 40 60 80 5 0 5030 502000 2500 3000 3500

3065 3094 3057 3077 3075 3016 2963 3024 2970 2923 2963 2985 2913 2938 2876 2907 2905 2779 2869 2853 2713 2728 2728 NNW RADRMNSPECTRA RAMAN AND IR UNKNOWN

1897 1800

Wavenumber (cm 1788 1782

601400 1600 1646 1651 1618 1649 1575 1516 1463 1476 1449 1461 1429 1446 1393 1413 –1 1378 1363 1374 ) 1293 1299 201000 1200 1269 1268 1218 1220 1194 1202 1211 1160 1111 1111 1059 1057 1020 1019 971 925 938 887 886

0 0 400 600 800 847 855 796 816 768 722 655 693 644 Neat/cap film Neat/cap film 565 545 531 3 522 503 495 433 413 418 4 376 302 259 220 179 180 %T %T IR IR Ra Ra Ra Ra I I 100 100 5.0 0.0 1.0 2.0 3.0 4.0 20 40 60 80 20 40 60 80 10 15 0 0 5

5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 3635 3544

3068 3098 3059 3048 2973 3012 2968 2931 2909 2944 2880 2941 2841 2881 2860 2861 2751 2750 .UKONI N AA SPECTRA RAMAN AND IR UNKNOWN 9.

2294 2250 2250

1924

1800

Wavenumber (cm 1745 1690 1627 1623 1581 1597 1509 1453 1464 1464 1463 1431 1427 1428 1439 1386 1376 1398

–1 1329 1343 ) 1262 1261 1268 1232 1232 1214 1163 1165 1097 1096 1076 1076 1049 1049 1021 1020 978 977 916 912 870 872 860 841 840 790 855 766 767 741 771 732 701 700 Neat/cap film Neat/cap film 559 567 5 566 558 533

529 6 511 478 437 408 379 409

252 Ra %T Ra %T IR IR I I 0.0 100 100 1.0 2.0 2.8 0.0 0.5 1.0 1.5 1.8 20 40 60 80 20 40 60 80 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500

3456 3330 3332 3177 2937 2960 2962 2908 2964 2876 2920 2874 2935 2873 29342874 2736 2738 2738 2669 NNW RADRMNSPECTRA RAMAN AND IR UNKNOWN 2472 2301 2235 2053 Wavenumber (cm

1464 1450 1466 1449 1456 1433 1436 1436 1379 1381 1380 –1 1339 1332 1339 ) 1298 1295 1253 1252 1260 1279 1222 1216 1181 1143 1150 1114 1114 1072 1073 1094 1072 1030 1046 1033 1032 1030 1011 966 992 902 952 901 888 880 887 828 847 854 810 806 804 749 738 755 739 660 686 Neat/cap film Neat/cap film Neat/cap

515 513 488 480 454 398 374 355 7 8 276 289 181 182 %T %T IR IR Ra Ra I I 100 100 0.0 1.0 2.0 3.0 10 20 28 20 40 60 80 20 40 60 80 0 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 3548

3326 3327 3169 3059 3088 3064 3004 2959 3003 3006 3030 2937 2938 2931 2930 2873 2913 2875 2873 2733 2736 SPECTRA RAMAN AND IR UNKNOWN 9. 2635

2415 2427

1952 1876 1810 Wavenumber (cm 1751 1672 1671 1607 1602 1586 1496 1461 1454 1457 1458 1440 1438 1379 1369 1347

–1 1303 1301 1300 ) 1289 1232 1209 1209 1233 1177 1131 1157 1094 1080 1091 1030 1038 1043 1043 1003 1021 1011 1003 969 916 912 892 815 859 890 816 799 780 752 735 738 698 648

621 Neat/cap film 641 595 595 Neat/cap film 508 533 485 461 468 409 420 375 9

10 337 %T %T Ra Ra IR IR I I 100 100 0.0 20 40 60 80 0.5 1.0 1.5 1.8 0.0 20 40 60 80 0 1.0 2.0 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 H 2 3433 O

3114 2966 2963 2907 2906 2809 NNW RADRMNSPECTRA RAMAN AND IR UNKNOWN Wavenumber (cm H 2

O 1630

1445 1467 1413 1412 1385 –1

) 1265 1261

1092 1111 1020

867 864 790 800 809 710 702 688 687 662 Smear B disc KBr 491 474 12 11 183 184 %T %T IR IR Ra Ra Ra Ra I I 100 100 0.0 20 40 60 80 1.0 2.0 3.0 20 40 60 80 0 2 4 6 8 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500

2962 2967 2975 2889 2916 2963 2855 2855 2876 2860 2754 2719 2719 SPECTRA RAMAN AND IR UNKNOWN 9. 2694 2682

1977 1967 Wavenumber (cm

1488 1444 1455 1451 1460 1399 1367 1366 1365 1332 –1 1305 1290

) 1255 1217 1227 1241 1181 1128 1121 1083 1071 1070 1048 1015 1029

889 914 911 853 874 835

658 614 Neat/cap film Neat/cap Neat/cap film Neat/cap 488 435 14 13 288 %T %T IR IR Ra Ra I I 100 70 90 60 80 0.0 100 10 20 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 20 40 60 80 Neat/cap film Neat/cap 3500

3416 3331

3296 3172 3092 3000 3072 3063 2914 3007 3003 2895 2899 2944 2956 2857 2837 2836 2500

2548 SPECTRA RAMAN AND IR UNKNOWN 2489 2000 2030 1800 1840 1794 Wavenumber (cm 1733

1600 1701 1642 1601 1604 1601 1588 1588

1400 1498 1470 1456 1468 1422 1379 1442

–1 1339 1337 1336 1303

) 1303

1200 1316 1260 1250 1248 1248 1205 1174 1173 1118 1160 1105 1154 00800 1000 1087 1050 1038 1077 1026 1022 1041 1003 996 987 898 897 871 883 785 784 758 755 712 711

ID Components 692 0 400 600 656 ofpaper:ATR 614 553 553 508 511 436 443

378 15 16

279 261 185 212 186 %T %T IR IR Ra Ra I I 100 100 0.0 20 40 60 80 1.0 2.0 3.0 20 40 60 80 0.0 0 1.0 2.0 uo mull Nujol Neat/Cap film Neat/Cap 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500

3277 3187 3024 3049 2963 Nujol 2998 3046 2997 3000 2925 2916 2876 2934 2875 2867 2739 2736

2720 SPECTRA RAMAN AND IR UNKNOWN 9. 2607 2636

2256 Hint: Ether Hint:

1838 Wavenumber (cm

1716 1664 1662 1626 1483

1484 Nujol 1451 1465 1432 1451 1456 1412 1410 1378

–1 1380 1380 1362 ) 1303 1296 1306 1258 1258 1245 1167 1202 1209 1132 1131 1159 1156 1111 1113 1097 1043 1044 1071 1010 1007 1004 988 942 942 921 883 883 851 831 831 846 795 794 765 772 765 734 733 722

538 478 477 517 431 431 411 18

386 17 340 %T %T IR IR Ra Ra I I 100 100 0.0 2.0 4.0 0.0 20 40 60 80 20 40 60 80 2.0 4.0 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500

3421 3423 3339 3262 3078 3063 3064 2910 2930 2794 2674 NNW RADRMNSPECTRA RAMAN AND IR UNKNOWN

2081

1924 Wavenumber (cm

1703 1641 1607 1604 1587 1591 1489 1538 1460 1461 1474 –1 1441

) 1420 1381 1367 1338 1320 1297 1264 1243 1261 1243 1203 1155 1156 1153 1126 1080 1089 1049 1071 1065 1017 1000 997 940 930 896 865 880 861 838 766 766 764 709 709 689 672 ATR B disc KBr 577 575 528 538 478 440 438 415 20 357 19

309 187 253 188 %T %T IR IR Ra Ra I I 100 100 20 40 60 80 0.0 2.0 4.0 20 40 60 80 10 0 5 Neat/Cap film

3500 3628 H 2 3433 O 3417 0020 001800 2000 2500 3000 3011 3003 2929 2934 29212960 2876 2935 2854 2875 2736 .UKONI N AA SPECTRA RAMAN AND IR UNKNOWN 9. Wavenumber (cm

1714 1716 1600 1580

1400 1466 1452 1444 1453 –1 1415 1415 1412 ) 1343 1358 1302

1200 1259 1231 1169 1168 1113 1111 1000 1046 1057 1011 1012 994 960 926 923 873 896 800 818 772 724 723

0 400 600 655 650 626 622 590 589 540 462 disc KBr 474 475 21 22 323 %T %T IR IR Ra Ra I I 0.0 100 100 2.0 4.0 6.0 0.0 2.0 4.0 6.0 8.0 20 40 60 80 20 40 60 80 Neat, cap film Neat, cap Neat, cap film Neat, cap 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500

3204 2969 2968 2927 2963 2928 2969 2925 2915 2916 2866 2912 2875 2872 2866 2809 2835 2721 2722 2835 2730 2573 2556 NNW RADRMNSPECTRA RAMAN AND IR UNKNOWN Note: compound contains S compoundcontains Note: Note: compound contains S compoundcontains Note: Wavenumber (cm

1462 1451 1449 1451 1445 1384 1437 –1 1385 1428 1375 ) 1316 1368 1321 1320 1247 1247 1265 1265 1161 1159 1126 1066 1084 1061 1061 1060 1045 981 970 953 929 955 892 893 857 861 784 726 758 678 655 631 630 654

415 24

339 353 23

273 189 211 190 %T %T IR IR Ra Ra I I 100 100 20 60 80 10 20 40 60 80 40 0 10 2 4 6 8 0 Neat/Cap film Neat/Cap film 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 Note: compound contains F compoundcontains Note: 3079 3090 3086 3061 F contains compound Note: 3040 3047 2967 2956 2923 2923 2869 2866 .UKONI N AA SPECTRA RAMAN AND IR UNKNOWN 9.

1930 Wavenumber (cm

1743 1628 1627 1619 1619 1607 1595 1590 1490 1489 1456 1445 1459 –1

) 1353 1354 1381 1309 1280 1265 1265 1180 1251 1251 1182 1137 1134 1160 1142 1101 1079 1079 1071 1071 1041 1004 1004 1004 977 925 911 887 831 857 810 777 751 700 728 728 682 649 679 557 528 528 514 444 391 25

349 26 282 297 245 %T %T IR IR Ra Ra I I 100 10 100 20 40 60 80 0 20 40 60 80 10 5 0 Neat/Cap film Neat/Cap film 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500

3550 H 2

3470 O Note: compound contains Cl compoundcontains Note:

3146 3184 3071 3083 3082 3071 3044 2939 2939

2530 SPECTRA RAMAN AND IR UNKNOWN Wavenumber (cm 1797 1796 1765 1767 1764 1765 1743

1575 1575 1595 1594 1548 1547 1493 1434 1433 –1 1431

) 1369 1372 1371

1264 1217 1204 1204 1195 1194 1149 1147 1163 1163 1076 1072 1070 1075 1025 1026 1007 1013 926 885 885 892 859 815 800 800 815 751 750 720 692 665 664 597 596 617 594 545 544 530 530 499 458 457 431 430 381 28 338 27 191 280 271 192 %T %T IR IR Ra Ra I I 100 0.0 1.0 2.0 3.0 100 0.0 20 40 60 80 1.0 2.0 3.0 4.0 5.0 20 40 60 80 Neat/Cap film 3500 3544 3475 3484 3439 3000

2974 Nujol 3073 2898 2960 3071 2929 2937 2931 2889 2875 2873 2855 2731 2734 2861 5020 8010 1400 1600 1800 2000 2500 .UKONI N AA SPECTRA RAMAN AND IR UNKNOWN 9. Note: Compound containsS Note:

and is a monohydrate and is 2233 2096 Wavenumber (cm

1727 1729

1625 1601 1600 1580 1580

Nujol 1488 1459 1461 1463 1441 1450

–1 1420 1377 1384 1381 ) 1287 1304 1309 1200 1272 1272 1274 1290 1201 1213 1246 1195 1178 1187 1164 1116 1124 1123 1000 1058 1056 1040 1073 1040 1022 960 959 893 894

800 859 798 795 834 771 743 725 705

600 662 652 652 612 607

534 535 mull Nujol 477 400 446 400 29 351 30

243 237 %T IR %T Ra IR Ra I I 100 0.0 100 20 40 60 80 0.4 0.8 1.2 20 40 60 80 4 6 8 0 2 Neat cap film Neat cap 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500

3398 3410 3378 3367 3285 3315 3314 3291 3193 2960 2963 2946 disc KBr 2945 2936 2962 2892 2914 2877 2922 2892 2797 2876 2695 2735

2542 SPECTRA RAMAN AND IR UNKNOWN aeubr(cm Wavenumber

1630 1611

1460 1457 1460 1445 1461 –1 1403 1445 ) 1371 1382 1380 1377 1345 1341 1358 1356 1272 1296 1280 1225 1181 1148 1150 1153 1150 1119 1112 1074 1055 1051 1045 1021 1025 1040 996 983 975 914 916 905 921 842 839 845 861 776 773 809 772 753 769 727 649 622 580 542 558 440 463 405 397 31

362 32

288 193 232 194 %T IR %T Ra IR Ra I I 100 100 0.0 1.0 2.0 3.0 40 60 80 20 40 60 80 0 2 4 6 8 ATR

3500 3626 3626

3000 3060 3070 3054 3067 3026 3001 2968 2907 2923 2915 2854 2851

2500 2715 .UKONI N AA SPECTRA RAMAN AND IR UNKNOWN 9. uo mull Nujol 2000 1800 Impurity Wavenumber (cm 1759 1727 1600

1603 1601 1604 1603 1584 1590 1482

1400 1493 1472 1452 1450 1452 1451 1432 –1 1396

) 1372 1379 1363 1331 1307

1200 1296 1231 1246 1183 1181 1198 1214 1156 1154 1152 1152 1120

1000 1070 1032 1027 1002 1028 1033 949 935 906 934 888

800 866 794 813 811 761 754 775 770 695 600 622 631 619 566 580

400 470 410 389 34

322 33 285 224 UNKNOWN IR AND RAMAN SPECTRA 195

100 898 961 3287 80 1206 1302 1337 1096 735 60 1378

IR 1131 40 %T 1464 2809

Neat cap film 2873 35 2958 1444 2928

3.0 280 2874 2963 2937 1299 834 2.0 879 2811 Ra 896 1059 I 2734 1135 403 1.0 3326

0.0

100 621 1709

80 1084 3378 1008 932 781 1419 883 1218 3062 1378

60 H2O 1488 705 3002 IR 40 728 1466 %T 1457

20 Smear 2955 36 1004 2854 2924 2.0 Note: Quaternary amine salt 2852 Ra 2891 2925 I 1.0 281 621 1442 1032 1218 731 837 3061 1605 1302 1082 881 1159 1586 2732

0.0

3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber (cm–1) 196 %T %T IR IR Ra Ra Ra Ra I I 100 100 0.0 2.0 4.0 20 40 60 80 20 40 60 80 0 2 4 6 Neat cap film Neat cap B disc KBr 5030 5020 8010 4010 008060400 600 800 1000 1200 1400 1600 1800 2000 2500 3000 3500 H 2

O 3435 3289 3290 3145 3060 3056 3086 2976 2976 2963 2991 2935 2936 2879

Note: Contains P Contains Note: 2877 2741 .UKONI N AA SPECTRA RAMAN AND IR UNKNOWN 9. Wavenumber (cm H 2 O

1624 1651 1654 1593 1591 1575 1556 1485 1439 1452 1440 –1

) 1373 1373 1312 1298 1296

1191 1180 1152 1152 1121 1096 1076 1030 1041 1003 996 1003 1003 936 936 891 862 755 777 722 721 685 697 620 618 602 538 458 466 465 392 384 37 38 292 297 250 %T %T IR IR Ra Ra I I 100 0.0 100 2.0 4.0 6.0 0.0 20 40 60 80 0.4 0.8 1.2 1.6 20 40 60 80 Neat cap film Neat cap B disc KBr 5030 502000 2500 3000 3500

3416 3279 3076 3081 3048 2963 2937 2959 2963 3042 2909 2926 2926 2875 2935 2910 2874

2736 Boron Contains Note: NNW RADRMNSPECTRA RAMAN AND IR UNKNOWN Note: Contains Boron Contains Note:

2145

1926 1800 Wavenumber (cm 6010 1200 1400 1600 1616 1615 1589 1591 1555 1485 1557 1483 1483 1450 1431 1466 1444 1417 1425 1378 1359 1337 –1 1299 1297 1284 1310

) 1262 1260 1283 1231 1222 1223 1149 1167 1171 1150 1129 1120 1118 1091 1000 1070 1073 1071 1031 1029 1003 962 968 959 904 877 0 600 800 825 832 805 835 815 772 768 741 752 750 715 692 695 666 670 626 532 511

400 439 39

40 336

237 197 198 9. UNKNOWN IR AND RAMAN SPECTRA

100

80 760 3025 1494 3078 1180 1026 1088 60 1456 IR %T 580

40 689 2854 1603

20 1309 996 2925 703 1381 Nujol Mull 1442 41 1368 1350

Note: Purchased as Phenyl Boronic Acid with an HPLC assay of 97% Ra I 10 1603 223 3057 1341 619 1160 800 661 1181 1574 420 1314 1367 3144 2994 0 100

80 2752 2852 2920 1408 1477 1330

60 856 1118 1635 636 559 IR 750

%T 1367 40 3175

20 3331 1337 KBr disc 1738 42 1726

8 346 Ra I 1573 1119

4 707 429 961 656 1710 1801 1660 3317 3162

0 3500 3000 2500 2000 1800 1600 1400 1200 1000 800 600 400 Wavenumber (cm–1) %T %T IR IR Ra Ra Ra Ra I I 100 100 20 40 60 80 20 40 60 80 0 12 16 0 2 4 6 8 4 8 B disc KBr uo mull Nujol Note: Nitrogen 6 member ring aromatic heterocycle aromatic ring member Nitrogen 6 Note: Note: Nitrogen 5 member ring aromatic heterocycle aromatic ring member Nitrogen 5 Note: 5030 5020 1800 2000 2500 3000 3500 3469 3470 3419 3419 3330 3334 3123 3130 3120 3091 2981 3029 2925 2921 2853 2865 2745 2684 2747 2646

2486 SPECTRA RAMAN AND IR UNKNOWN

2199 Wavenumber (cm 1824

1600 1659 1650 1632 1569 1579 1556 1550 1535 1509 1473

4010 1000 1200 1400 1467

–1 1443 1437 1447 1444 ) 1384 1383 1304 1302 1265 1265 1236 1232 1195 1193

1089 1087 1027 998 995 984 978 927 926 800 814 827 780 767 758 762 732

600 676 661 669 617 626 583 584

400 463 388 348

378 44 43 199 284 200 9. UNKNOWN IR AND RAMAN SPECTRA

1. Cyclohexane: 2930, 2855 CH2 (note no 2960 CH3), 1452 CH2 (note no 1378 CH3), (note no 723 CH2 chain).

2. e 2,4-dimethyl pentane: 2965 CH3 o.ph. str., 2940 2850 CH3 and CH2 str., 1387, 1369 C(CH3)2 i.ph def, (note no 723 CH2 chain).

CH3 CH3

CH3CHCH2CHCH3

3. ¼ 2,5-dimethyl-1,5-hexadiene: 3080, 2980 CH2 str., 2950-2860 CH3 and CH2 str., 1780 2x890, ¼ ¼ 1650 C C str., 1450 CH2 and CH3 def, 890 R2C CH2 CH wag.

CH3

H3C H2C C

C CH2 CH2

H2C

4. 1 e 1 4-tert-butyltoluene: Aliphatic group: 2965, 2876 cm CH3 str. 1470 1460 cm CH3, 1392, 1 1 e 1 1363 cm C(CH3)3, 1375 cm CH3. Aromatic group: 3100 3000 cm aromatic CH str., 1517, 1407 cm 1 para aromatic ring, 817 cm 1 2 adj aryl H.

H3C C(CH3)3

5. e e 1-methyl naphthalene: 3100 3000 arom CH, 2975 2860 CH3, 1597, 1510, 1398 aromatic ring, 1462, 1378 CH3, 790 3 adj aryl H, 772 4 adj aryl H.

CH3 UNKNOWN IR AND RAMAN SPECTRA 201

6. h e h n-Butyronitrile: 2970 CH3, 2250 C N str., 1460 CH3,CH2 def, 1425 CH2( C N) def 1375 CH3 i.ph. def.

H2C CN

H3C CH2

7. 1 1 e 2-Hexyne: Aliphatic group 2964/2873 cm CH3 str., 2935, 2920 cm CH2 str., 1464 1 h 1450 cm CH3/CH2 def, 1380 CH3 i. ph. def., 1339 CH2 wag. Acetylene group, C C str in Raman at 2301 and 2235 cm 1 (Fermi resonance), 375 cm 1 CeChC bend (Raman).

H2C CH3

H3C CC CH2

8. 1 e n-Butanol: Aliphatic group: 2960, 2874 cm CH3 str., 2935 CH2 str., 1470 1450 CH3,CH2 1 def, 1378 CH3 i.ph def. Hydroxy group (primary alcohol): 3300 cm OH str., 1420 broad e e e w 1 OH bend, 1070 1025 involves C O str of CH2 OH, 660 cm (broad) OH wag.

HO H2C CH3

H2C CH2

9. 1 Trans-2-Hexen-1-ol: Aliphatic group: 2959, 2873 cm CH3 str., 1458 CH3,CH2 def, 1379 1 1 ¼ CH3 i.ph def. Oleﬁnic group: 3004 cm CH str., 1672 cm C C str., 1300 trans CH rk, 969 cm 1 (IR) trans CH wag. Hydroxy group (primary alcohol): 3327 cm 1 OH str., 1091, 1043, 1091 cm 1 involves CeO str., w650 cm 1 (broad) OH wag.

H C H2 CH OH C 2 C H3C H C H2

10. e Benzyl alcohol: 3330 OH, 3100 3000 arom CH, 2925, 2870 CH2, 1600, 1493 arom ring, e 1452 CH2/arom ring, 1420 broad OH, 1015 CH2 OH, 735 5 adj H, 696 arom ring.

CH2 202 9. UNKNOWN IR AND RAMAN SPECTRA

11. e e e Silicon dioxide: SiO2 1130 1000 IR strong (involves O Si O o. ph. str.). Note:featureless Raman spectrum.

12. e Dow Corning vacuum grease, dimethyl siloxane polymer: 2966 2963 CH3 o. ph. str., e w e 2907 2906 CH3 i. ph. str., 1412 CH3 o. ph. def, 1261 CH3 i. ph. def, 1090 1020 IR involves SieOeSi str.

CH3 CH3

* O Si O Si *

CH CH 3 3 N

13. Tetrahydrofuran: Aliphatic 2975e2860 suggests only methylene. Two bands at 1070 and 911 cm 1 suggest ether (CeOeC out-of-ph. and in-ph. str., respectively).

O 14. e e 1 1,4-Dioxane: Aliphatic 2955 2850 CH2, 1450 1442 CH2, 1362 O CH2 wag, 1120 cm involves CeOeC o. ph. str. 900e830 cm 1 involves CeOeC in-phs. str.

O 15. e e 1 Anisole: 3100 3000 aromatic CH, 3000 2838 CH3(O), 1602, 1588, 1498 cm aromatic 1 þ 1 ring, 1468, 1452, 1440 cm CH3(O) aromatic ring, 996 cm (Raman) 2,4,6 C Radial e 1 1 i.ph.str., 1247, 1040 arom-O CH3, 752 cm 5 adjacent aryl H, 690 cm aromatic ring.

CH3

16. Paper: Mostly cellulose and carbonate, some water, with a trace of organic sizing: carbonyl and oleﬁnic.

17. Trans, trans-2,4-Hexadien-1-ol: Oleﬁnic group, 3024, 3003 cm 1 CH str., 1672 cm 1 C ¼C str., 1300 cm 1 trans CH rk, 988 cm 1 (IR) trans CH wag (note higher frequency due to adjacent trans, trans oleﬁn). Hydroxy (primary alcohol) group. 3277, 3187 cm 1 OH str., 1097, 1071, w1000 (shoulder) cm 1 involves CeO str. UNKNOWN IR AND RAMAN SPECTRA 203

18. 1 1,2-Epoxypentane: Aliphatic CH str with epoxy CH2 o. ph. str at ca. 3050 cm and CH2 def. at 1483 cm 1. Epoxy CeOeC in-ph str. At 1258 cm 1 (both IR and Raman) and CeOeC out-of-ph str at 831 cm 1. Aliphatic peak intensity of methylene (2935 cm 1) to methyl (2875 cm 1) consistent with ca. 2 methylene to 1 methyl group.

CH2CH2CH3

19. Meta (3) chlorophenol:3360cm 1 OH str., 3100e3000 aryl CH str (note no aliphatic e 1 1 1 (CH2,CH3)3000 2800 cm , 1605, 1592, 1478, 1448 cm aryl ring, 1000 cm (Raman) 2,4,6 C Radial i.ph.str., 1245e1190 cm 1 involves aryl-OH str, 852 lone H, 772 3 adj H, 680 aryl ring.

HO Cl

20. Dextrin: Polysaccaride/carbohydrate: 3421 cm 1 OH str., 1338 cm 1 OH def., 1155, 1080, 1017 cm 1 involves CeOstr.ofCeOH/CeOeC polysaccharide ring system. Axial connection similar to starch result in characteristic IR bands 930, 861, 766, and 709 involving the ring in-phase and semi-circle str. The cluster of Raman bands centered around the intense 478 cm 1 band also is diagnostic of the axial type connection. Presence of water is evident from bands at 2081 (combination) and 1641 cm 1 (def.). 1 Biopolymeric aliphatic: CH2 and CH str bands between 2930 and 2820 cm and CH2 def at 1460 cm 1.

O O *

OH OH n 204 9. UNKNOWN IR AND RAMAN SPECTRA

21. 2-Hexanone: Ketone C ¼O str 1716 cm 1and C ¼O overtone at 3417 cm 1. 1412 cm 1 from e ¼ e 1 CH2 (C O) and 1358 1380 cm from CH3 i.ph def. Aliphatic group: CH2 and CH3 stretches at 2935, 2875 , and 2960 cm 1, respectively. Peak intensity of methylene (2935 cm 1) to methyl (2875 cm 1) consistent with ca. 3 methylene to 2 methyl. No evidence of branching in Raman spectra.

22. Sodium acetate: Simple IR and Raman spectra. Dominant IR bands at 1580 and 1444 cm 1 indicate a carboxylate salt (CO2 out-of-phase and in-phase stretch, respectively).

O Na

23. e 1 Ethyl methyl sulﬁde: Aliphatic group. The CH2 S has bands at 2928 cm from the CH2 e 1 1 o.ph.str., 2872 875 cm from the CH2 i.ph.str., 1265 cm (IR) from the CH2 wag and e 1 e 1 1437 1428 cm from the CH2 def. The CH3 S has bands at 2969 cm from the CH3 1 1 o.ph.str., 2915 cm from the CH3 i.ph.str., the 1375 cm is from the CH3 i.ph.def. and 1 þ e bands between 1070 and 950 cm involve the CH3 rock C C str. Bands involving the CeSeC str are observed between 780 and 650 cm 1.

H3C CH2CH3 S

24. 2-Propanethiol: SH group: SH str results in characteristic band at 2550e2580 cm 1. 1 Aliphatic group: The isopropyl group has characteristic bands at 2963 cm (CH3 1 e 1 o.ph.str), 2866 cm (CH3 i.ph.str), 1462 1451 cm (CH3 o. ph. def.), and in the IR 1 e e spectrum at 1384, 1368 cm (CH3 i.ph. def). The CH S group has bands at 2912 2930 cm 1 (CH str.) and 1247 cm 1 (CH wag). The isopropyl CeC/CeS str results in 1 e a strong Raman band at 631 cm involving the in-phase (C)2C S str.

H3C

CH SH

H3C UNKNOWN IR AND RAMAN SPECTRA 205

25. e 1 3-Fluorotoluene (1-ﬂuoro-3-methylbenzene): Aliphatic (CH3) 2967 2866 cm methyl CH3 1 1 e 1 str., 1459 cm CH3 o. ph. def, 1381 cm CH3 i. ph. def. Aromatic group: 3100 3000 cm aryl CH str., 1619e1590 cm 1 aryl ring quadrant str. (IR/Raman), 1489 cm 1 (IR) aryl ring semi-circle str., 1004 cm 1 (Raman) 2,4,6 C Radial i.ph.str., 857 cm 1 lone H wag, 777 cm 1 (IR) 3 adj H wag, 682 cm 1 (IR) ring pucker. Aryl-F results in IR/Raman bands at 1265, 1251 cm 1 involving the Aryl-F str.

F CH3

26. 1,3-Bis(triﬂuoromethyl)benzene: Note no aliphatic observed. Aromatic group: 3100e3000 cm 1 aryl CH str., 1628e1607 cm 1 aryl ring quadrant str. (IR/Raman), 1004 cm 1 (Raman) 2,4,6 C Radial i.ph.str., 911 cm 1 lone H wag, 810 cm 1 (IR) 3 adj H wag, 1 700 cm (IR) ring pucker. CF3 group: 1354, 1309, 1280 involves CF3 o. ph. str., 1181, 1 1134 cm involves CF3 i. ph. str.

F3C CF3

27. Phenyl acetate: Aromatic group: 3100e3000 cm 1 aryl CH str., 1594 cm 1 aryl ring quadrant str. (IR/Raman), 1493 cm 1 (IR) aryl ring semi-circle str 1007 cm 1 (Raman) 2,4,6 C Radial i.ph.str., 750 cm 1 (IR/Raman) 5 adjacent H wag, 692 cm 1 aryl ring e 1 ¼ 1 pucker. Acetate group: 1765 1740 cm C O str., 1431 cm (O)CH3 o. ph. def., 1371 1 e 1 fe e e 1 cm (O)CH3 i. ph. def., 1217 1163 cm involves O C C o. ph. str., 815 cm fe e e 1 involves O C C i. ph. str.. 2939 cm CH3 o. ph. st.

C O

H3C 206 9. UNKNOWN IR AND RAMAN SPECTRA

28. 2,4,6-Trichlorobenzoyl chloride: Aromatic group: 3146e3082 cm 1 aryl CH str., 1575e1547 cm 1 aryl ring quadrant str. (IR/Raman), 1434 cm 1 (IR) aryl ring semi-circle str. The band at 800 cm 1 derives from the lone H wag and the band at 720 cm 1 involves the aryl ring pucker. The band at 1075 cm 1 (IR/Raman) involves the aryl-Cl str. Aromatic acid chloride group: 1796 cm 1 C ¼O str. and the weaker band at 1767 cm 1 involves the overtone of the 885 cm 1 that is Fermi resonance enhanced with the carbonyl. The 885 cm 1 and 1204 cm 1 involves the (aryl)CeC(¼O) str.

Cl O

Cl Cl

29. 1 Dioctyl phthalate: Aliphatic group: CH2 stretches at 2931, 2873 cm and CH3 stretches at 2960 and 2861 cm 1, respectively. Peak intensity of methylene (2931 cm 1) to methyl (2960 cm 1) consistent with ca. 4 methylene to 2 methyl. Methylene and methyl deformation bands are observed at 1463 and 1381 cm 1. Phthalate Carbonyl Group: C ¼O str (IR/Raman) at 1727 cm 1, band cluster between 1290 and 1270 cm 1 involves CeCeO o. ph. str. and the band at 1040 cm 1 involves the CeCeO i. ph. str. The band at 1123 involves the OeC str of the aliphatic group. Aromatic group: 3100e3000 cm 1 aryl CH str., 1601e1580 cm 1 aryl ring quadrant str. (IR/Raman), 1488 cm 1 (IR) aryl ring semi-circle str. The band at 743 cm 1 derives from the 4 adj H wag.

O UNKNOWN IR AND RAMAN SPECTRA 207

30. 1-Hexane sulfonic acid sodium salt (sodium 1-hexanesulfonate): Note sample was prepared as a nujol mull which interferes with IR aliphatic bands. Raman aliphatic bands indicates both methyl and methylene groups. No aromatic observed. The water results in bands in the IR spectrum at 3544 and 3484 cm 1 from the OH str., 1625 cm 1 from the OH def., a combination bands at 2233 and 2096 cm 1 and the broad OH bend at ca. 622 cm 1. Sulfonic acid salt group: Strong IR bands from 1213 to1187 cm 1 derive from the 1 SO3 o. ph. str. The strong IR/Raman band at ca. 1058 cm derives from the SO3 i. ph. str. The band at ca. 795 cm 1 (IR/Raman) involves the CeS str. O

H3C (H2C)5 S O Na

O 31. 1 3-Amino pentane: Aliphatic group: CH3 stretches at 2962, 2876 cm and CH2 stretch at 2922 cm 1, respectively. The peak intensity of methylene (2922 cm 1) to methyl (22962 cm 1) is consistent with ca. 1 methylene to 1 methyl. Aliphatic bands from methyl and methylene deformation vibrations are observed at 1461, 1377 and 1 1356 cm . Primary Amine group: The NH2 stretching vibrations result in a doublet between 3380 and 3290 cm 1 with a shoulder at 3193 cm 1 which derives from an 1 overtone (Fermi-resonance enhanced) of the 1611 cm NH2 deformation band. The 1 band cluster from 921 to 769 cm derives from the NH2 wag and twist vibrations. Bands involving the CeN stretch occur at w1150 and w1045 cm 1.

NH2

32. a-D-Glucose: Water: The band at 1630 cm 1 indicates some water is present in the KBr disc preparation. Aliphatic group: CH2 and CH str vibrations are observed between 2945 and 1 1 2892 cm . The CH2 deformation has a strong characteristic band at 160 cm . Hydroxyl group: OH stretch at 3410, 3315 cm 1. Note different hydrogen bonding environments. OH def at ca. 1345 cm 1. Bands between 1150 and 996 cm 1 involve the CeO str of e e primary and secondary alcohols. Primary alcohols ( CH2 OH) are mostly the lower frequency 1025e1000 cm 1 band cluster and the secondary alcohols (>CHeOH) are mostly the 1150, 1112 cm 1 bands. The cyclic ether has bands at w 1120e1110 involving the CeOeC o. ph. str. and at w840 cm 1 from the CeOeC i. ph.str.

H OH

H O HO HO H H OH

H OH 208 9. UNKNOWN IR AND RAMAN SPECTRA

33. Butylated hydroxy toluene: Note Nujol mull aliphatic interference. Aliphatic group: 2968, w 1 e 1 1 2876 cm CH3 str. 1472 1450 cm CH3 o.ph. def., t-butyl 1396, 1363 cm C(CH3)3 i. 1 e 1 ph. def., 1375 cm CH3 i. ph. def. Aromatic group: 3100 3000 cm aromatic CH str., 1604e1590 cm 1 (IR/R) quadrant ring str., 1482, 1432 cm 1 (IR) semi-circle str., 866 cm 1 (IR) aryl lone H wag. Phenol hydroxyl group: 3626 (IR/R) OH str., 1246e1198 cm 1 (IR/R) involves aryl-O str.

CH3 OH CH3 H3C CH3

H3C CH3

CH3

34. e 1 Polystyrene: Aliphatic group: 2923 2854 cm CH2 str. 1452 CH2 def. Aromatic group: 3100e3000 cm 1 aromatic CH, 1603, 1584, 1493 cm 1 aromatic ring quad and semi-circle str., 1002 cm 1 (Raman) 2,4,6 C Radial i. ph.str., 754 cm 1 (IR) 5 adjacent aryl H, 695 cm 1 (IR) aromatic ring pucker.

H2 * C CH *

35. 1 1 1 Di-n-butyl amine: Aliphatic group: 2964/2958 cm and 2873 cm CH3 str., 2928 cm (IR) CH2 o. ph. str., Note multiple bands in Raman from trans and gauche methylene 1 1 groups. 1298 cm (Raman) CH2 twist of chain. 1464/1445 cm involves methyl 1 and methylene deformation. 1378 cm CH3 i. ph. def. Secondary amine group: 3287 1 1 1 e e 1 cm NH str., 2809 cm CH2 (N) i. ph. str., 1131 cm C N C o. ph. str., 735 cm NH wag.

(CH2)3CH3

(CH2)3CH3 UNKNOWN IR AND RAMAN SPECTRA 209

36. Benzalkonium chloride: Aromatic group: 3100e3000 aromatic CH, w1600, 1488 cm 1 aromatic ring quad and semi-circle str., 1002 cm 1 (Raman) 2,4,6 C Radial i. ph.str., 728 cm 1 (IR) 5 adjacent aryl H, 705 cm 1 (IR) aromatic ring pucker. Quaternary amine þ 1 1 salt: (N )CH3 has CH3 o. ph. str. at 3002 cm , the CH3 i. ph. str. at 2852 cm , the 1 CH3 o. ph. bend/def at 1488 cm . The NC4 i. ph. str. is expected between 800 and 950 cm 1 and may possibly be assigned to the band at 837 cm 1.

Cl N

C7H15

37. 1 1 n-Ethyl acetamide: Aliphatic group: 2976, 2877 cm CH3 str., 2936 CH2 str., 1452 cm 1 1 ¼ CH3/CH2 def., 1373 CH3 i. ph. def. Amide group: 3290 cm NH str., 1654 cm C O str., 1556 cm 1 CNH str./bend, 3086 cm 1 overtone of 1556 cm 1 band (2 1556), 1298 cm 1 CNH str./open, 721 cm 1 NH wag.

H O N

C CH2CH3

CH3

38. Triphenyl phosphine oxide: Aromatic group: 3100e3000 aromatic CH str., 1593, 1575, 1485/ 1439 cm 1 aromatic ring quad and semi-circle str., 1121 cm 1 involves P-aryl str., 1003 cm 1 (Raman) 2,4,6 C Radial i.ph.str., 755 cm 1 (IR) 5 adjacent aryl H, 697 cm 1 (IR) aromatic ring pucker. Phosphine oxide (P ¼O) group: 1191/1180 cm 1 (IR/Raman) P ¼O str.

P O 210 9. UNKNOWN IR AND RAMAN SPECTRA

39. 4-Methyl-pyridine-3-boronic acid: Boronic acid group: 3420e3200 cm 1 (broad) OH str., 1359 cm 1 involves BeO str., 1071 cm 1 BeOH def., 772 (B)OH wag. Pyridine group: 3080e3040 cm 1 aryl CH str., 1615, 1591, 1555 aryl quadrant str., 1480e1425 cm 1 involves aryl semi-circle str., 1091 cm 1 involves 2,4,6 C Radial i.ph.str., 1003 cm 1 involves the whole ring breath (str). 877 cm 1 lone H wag, 835 cm 1 2 adj H wag.

CH3 OH

B OH

40. 1 1 Tributyl borate: Aliphatic group: 2959 and 2874 cm CH3 str., 2935 CH2 o. ph. str., 1485 cm e 1 e 1 (O)CH2 def., 1466 1458 cm CH3,CH2 def. Borate ester group: 1337 1297 cm involves 1 the B(O)3 o. ph. str., 832, 815 cm (Raman) most likely involves the B(O)3 i. ph. str., while 1 1 the 666 cm band (IR) is from the B(O)3 out-of-plane deformation. 1407 cm involves þ e 1 e the OCH2 wag B O str. Bands at 1073 and 1029 cm involve mostly the C O str.

C4H9 O

C4H9 B C4H9 O O

41. Phenyl boroxole: Phenyl boronic acid is a labile compound that in the solid state readily forms a Boron ether. The Boron ether when put in an acidic medium readily hydrolyzes to form the phenyl boronic acid. Raman spectrum indicates no aliphatic group is present (IR Nujol mull preparation interferes). No bands associated with the BeOH group are observed including the (B)OH str (w3250 cm 1), the BeOH bend (w1000 cm 1), and the BeOH wag (w800 cm 1) (see interpreted IR/Raman spectra # 64 of m-tolylboronic acid). Aromatic group: 3100e3000 cm 1 aromatic CH str., 1603, 1574, 1494/1442 cm 1 aromatic ring quad and semi-circle str., 1180 cm 1 involves B-aryl str., 996 cm 1 (Raman) 2,4,6 C Radial i.ph.str., 760 cm 1 (IR) 5 adjacent aryl H, 703 cm 1 (IR) aromatic ring pucker. BeO linkage: Strong characteristic IR bands involving the BeO str. are observed between 1381 and 1310 cm 1 in both the IR (strong) and Raman (moderate). UNKNOWN IR AND RAMAN SPECTRA 211

OH B O

3 B O B + H2O OH BO

42. 1 Azodicarbonamide:NH2 group: NH2 o. ph. and i. ph. str at 3331 and 3175 cm , respectively 1 1 (IR and Raman). NH2 bend/def at 1635 cm (IR). NH2 rk (Raman and IR) at 1118 cm 1 1 and the NH2 wag at 750 cm (IR) with an overtone 2 NH2 wag at 1477 cm . Amide C ¼Ogroup:C¼O str. in IR at 1738/1726 cm 1. The IR and Raman bands at 1367, 1337, and 1300 cm 1 involve the CeNstr.AzoN¼Ngroup:StrongRamanbandat 1573 cm 1 involves the N ¼Nstr.

C N NH2 H2N N C

43. 4-Methyl-imidazole:NeH group: This is characterized by complex hydrogen bonding involving NeH$$$N ¼ due to p-type hydrogen bonding of the unsaturated N atom in the heterocyclic ring. Thus a broad envelope of NH str vibrations are observed from 3400 to2700 cm 1 in the IR spectrum. The NH wag occurs at 926 cm 1 and the broad band at 1824 cm 1 is due to the Fermi-resonance enhanced overtone of the NH wag. Imadazole ring: Ring ¼CH str. bands at 3120, 3091, and 3029 cm 1. The out-of-phase C ¼C/C ¼N str. (Quadrant str.) results in bands between 1580 and 1509 cm 1 and the in-phase C ¼C/C¼N str. (semi-circle str.) results in bands at w1440 cm 1. The band cluster at 1304, 1265 cm 1 may involve the imidazole ring in-phase breathing mode. 1 Methyl group: Bands at 2921 and 2865 involve the CH3 str. and the band at 1384 cm involves the CH3 i. ph. def.

H 212 9. UNKNOWN IR AND RAMAN SPECTRA

44. e 1 Melamine: Amino group: 3500 3100 cm involves NH2 str. Note differences in hydrogen bonding (i.e., strongly hydrogen-bonded versus weakly hydrogen-bonded NH). e 1 w 1 1650 1620 cm doublet from NH2 deformation. 582 cm possibly NH2 wag. Triazine group: 1550 cm 1 quadrant ring str., 1470e1430 cm 1 semi-circle ring str., 984 cm 1 (Raman) N-Radial i. ph. str., 811 cm 1 ring pucker (sextant out-of-plane bend), 675 cm 1 quadrant in-plane ring bend.

H2N N NH2

NH2 APPENDIX IR Correlation Charts

Infrared group frequency correlation charts 3400 3300 3200 3100 3000 2900 2800 2700 1700 1600 1500 1400 1300 1200

CH , CH , CH, bend CH3, CH2, CH, stretch 3 2 C≡C–H R–CH3 Arom-H –CH(CH3)2

C=CH2 –C(CH3)3 C=CH

R–CH2–R R–CH3

R–O–CH3 Arom-CH3

R–CH2–R O=C–CH2– R–O–CH3 ≡ N C–CH2– R2–N–CH3 >C=CH O=C–H 2 O=C–H

O=C–CH 3600 3400 3200 3000 2800 2600 2400 2200 3

Si–CH3 X-H stretch R–OH …..O

O=C–OH……O

S–OH….. O

P–OH….. O

R–NH2

R–NH–R + − R–NH3 Cl

+ − R2–NH2 Cl

+ − R3–NH Cl

O=C–NH2 O=C–NH–C

O=C–NH–C cyclic

S–H P–H Si–H

213 214 IR CORRELATION CHARTS

2400 2300 2200 2100 2000 1900 1800 1900 1800 1700 1600 1500 1400 1300

C≡C C≡N, X=Y=Z str. C=O str. Cyclic anhydride CH –C≡N 2 R–CO–O–CO–R Conj C≡N R–CO–Cl S–C≡N C–C≡C–H R–CO–O–R –N=C=O CONH–CO–O–R –N=C=S H–CO–O–R R–CO–H

>C=C=CH2 Conj-CO–H R–CO–R Conj-CO–R Conj-CO-Conj R–CO–OH dimer R–CO–N − R–CO2

1700 1600 1500 1400 1000 900 800 700 600

.rtsC=C gawHCfelO

C=C R–CH=CH2

C=C R2C=CH2 R–CH=CH–R trans

C=C R–CH=CH–R trans

RCH=CR2 .rtsgniRrA gawH-rA

Ring mono, 1,3 or 1,3 5 Ring Lone Ar-H 2 adj Ar-H 3 adj Ar-H 4 & 5 adj Ar-H IR CORRELATION CHARTS 215

1400 130 120 1100 1000 900 800 1500 1400 1300 1200 1100 1000 900 800

C–O str. SO, PO, SiO str.

O=C–OH C–SO2–C

O=C–O–C C–SO2–N Ar-OH C–SO2–O–C R C–OH C–SO –Cl 3 2 R CH–OH 2 C–SO2–OH anhydride –CH –OH − + 2 C–SO3 H3O − + Epoxy C–SO3 Na Ar-O–CH 2 C2S=O

C=C–O–CH2 P=O

–CH2–O–CH2 P–O–CH2

Si–O

1700 1600 1500 1400 1300 1200 1100 1000 900 800 700

NH bend, CN str., NO str.

C–NH C–NH2 2

CH2–NH–CH2

Ar-NH2

+ C–NH3

+ C2–NH2

O=C–NH2

O=C–NH–C

C=N

C=N–O–C

CH2–NO2

Ar-NO2

C–O–NO2

C–O–N=O

Index

A AMD A. See Absorption intensity band assignments for, 48, 50e51t a. See Angle of incidence diffuse reflectance of, 53, 53f Absorbed radiation, 33 FT-IR calibration plot of, 49, 52f Absorption intensity (A), in attenuated total FT-Raman calibration plot of, 52, 52f reflectance, 41 quantitative analysis of, 48e53 Acetamide, 136, 149f spectra of, 48, 49e50f Acetamideoxime, 137, 159f Amide compounds Acetohydroxamic acid, 136, 152f IR and Raman spectra of, 136, 149f, 150f, 151f, 152f Acetone, 136, 145f spectra-structure correlations of, 101, 128 Acetonitrile, 135, 142f Amines Acetylene group, spectra-structure correlations of, IR and Raman spectra of, 137, 156f, 157f, 158f 124e125 spectra-structure correlations of, 126 Acetylenic compounds, spectra-structure correlations deformation vibrations, 128 of, 131e132 Amine salts Acid halides, spectra-structure correlations of, IR and Raman spectra of, 137, 156f, 157f, 158f 126e127 spectra-structure correlations of, 128 Acidic protons, spectra-structure correlations of, 126 Amino (NH) group Acrylamide, 136, 150f correlation chart for, 215 Acrylonitrile, 135, 142f environmental dependence of vibrational spectra AD. See Array detector and, 58e59 AETAC. See Poly-2-(acryloyloxy)-Ethyltrimethyl IR and Raman spectra of, 74, 74f Ammonium Chloride spectra-structure correlations of, 124e125, 133 Alcohols 3-Amino pentane, 193f, 207 group frequencies of, 104e105t Ammeline, 136, 151f IR and Raman spectra of, 136e137, 153f, 154f, 155f Ammonium, spectra-structure correlations of, 129 spectra-structure correlations of, 103e105, 104e105t, Ammonium chloride, 138, 167f 104f Amplitude Aldehydes in classical harmonic oscillator, 10, 10f spectra-structure correlations of, 126 dipole moment modulation by, 18, 18f stretching vibration for, 101 vibrational, dipole moment and, 15 Aliphatic groups Analyte concentration, IR and Raman signal and, IR and Raman spectra of, 135, 140f 45e46 spectra-structure correlations of, 74e78, 75f, 76t, 77f, Angle of incidence (a) 78f, 79t, 80f, 125e126 for attenuated total reflectance, 39e40, 40f conjugated, 79e99, 80e81t in dispersive systems, 27, 28f Aliphatic primary amines, IR and Raman spectra of, refractive index and, 33, 34f 73, 74f triatomic molecule stretches and, 65, 66f Aliphatic secondary amines, IR and Raman spectra of, Angle of radiation (b), in dispersive systems, 27, 28f 73, 74f Anharmonic oscillator, potential energy of, 13, 13f Alkane groups, spectra-structure correlations of, 74, Anhydrides 75f, 76t IR and Raman spectra of, 136, 145f, 146f, 147f, fluorinated, 130 148f, 149f Alkoxysilanes, spectra-structure correlations of, 131 spectra-structure correlations of, 100e101, 126e127

217 218 INDEX

Aniline, 137, 157f mono- and di-substituted, 88e89, 89f Anisole, 185f, 202 normal ring modes of, 86, 87f, 88t Anti-Stokes Raman scattering, 16f, 17 spectra-structure correlations of, 86e91, 87f, 88t, classical description of, 17e18, 18f 89f, 90f Aromatic rings stretching vibration of, 70, 70f correlation chart for, 214 Benzoic acid, 136, 148f IR and Raman spectra of, 136, 143f, 144f Benzyl alcohol, 182f, 202 spectra-structure correlations of, 128, 132 BH stretch, spectra-structure correlations of, 126 benzene, 86e91, 87f, 88r, 89f, 90f Bipolymers, IR and Raman spectra of, 139, 171f, 172f, conjugated, 79e99, 80e81t 173f, 174f, 175f, 176f fused, 92, 93t 1,3-Bis(trifluoromethyl)benzene, 190f, 205 heterocyclic, 93e99, 93f BLYP function, 24 Array detector (AD), signal-to-noise ratio and, 29 BeN type compounds Aryl CH wag, 90e91, 91t, 92f group frequencies of, 110, 111e112t Aryl groups, spectra-structure correlations of, 125 IR and Raman spectra of, 110, 110f Asymmetric vibrations, IR spectroscopy for, 1 spectra-structure correlations of, 110e112 Atmospheric compensation, for sample preparation, BeO type compounds 34, 120 group frequencies of, 110, 111e112t Atomic masses IR and Raman spectra of, 110, 110f in diatomic oscillator, 11 spectra-structure correlations of, 110e112, 129 in GF matrix method, 22 Boltzmann’s law, in Raman scattering, 17 ATR. See Attenuated total reflectance Bond angle, stretching frequency and, 101e102 Attenuated total reflectance (ATR), 39e41, 40f, 42t Boric acid, 139, 169f with microscopy, 44 Boronic acid compound, IR and Raman spectra of starch, 119e120, 120f of, 138, 161f Azo compounds 3-Bromo toluene, 138, 162f IR and Raman spectra of, 137, 160f 1-Bromohexane, 138, 161f spectra-structure correlations of, 127 1-Butanol, 137, 154f Azodicarbonamide, 198f, 211 n-Butanol, 181f, 201 Azo-tert-butane, 137, 160f n-Butyl acetate, 136, 145f t-Butyl alcohol, 137, 153f B N-Butyl methyl acrylamide, 136, 150f b. See Angle of radiation Butylated hydroxy toluene, 194f, 208 B3LYP function, 24 Butyric anhydride, 136, 146f n BaF2, in IR transmission, 32, 33t -Butyronitrile, 180f, 201 Band assignments, for PAM-AETAC samples, 48, 50e51t C Band intensities, for sample preparation, 33, 120 CaF2, in IR transmission, 32, 33t Band shape, in IR and Raman vibrational bands, 2 Calcium palmitic acid salt, IR spectroscopy v. Raman Baseline, for sample preparation, 34, 130 spectroscopy, 118f, 119 3-21G Basis set, 24 Calculating, vibrational spectra, 22e24 6-31G Basis set, 24 Capillary film, 35 Basis set, in vibrational spectra assessment, 24 Carbon dioxide (CO2) Beam splitter, in Michelson interferometer, 30e31, 31f center of symmetry of, 19, 19f Bending vibration. See Deformation vibrations Fermi resonance and, 60e62, 61f, 62t Bent triatomic molecule, as coupled oscillators, 64e65, fundamental vibrations for, 8, 9f 65f, 66f IR gas phase contours of, 55, 56f Benzalkonium chloride, 195f, 209 Carbonates, spectra-structure correlations of, 126e127, Benzamidine HCl, 137, 158f 129 Benzene. See also 1,3,5-Trisubstituted benzene Carbonyl groups Cartesian coordinate displacements for, 9, 9f environmental dependence of vibrational spectra center of symmetry of, 19, 19f and, 59 elementary ring vibrations of, 89, 90f group frequencies for, 100t INDEX 219

e See factors that effect, 99f, 101 103 CO2. Carbon dioxide IR and Raman spectra of, 99f Combination bands, anharmonic oscillators and, 13 review of, 99e101 Communication skills, for spectra interpretation, 117 spectra-structure correlations of, 99e103, 99f, 100t, Computer-based libraries, for spectral interpretation, 125, 126e127 122e123 Carboxylic acid dimers Configuration interaction (CI) method, 24 hydrogen bonding in, 58 Conjugation effects, in carbonyl groups, 102e103 IR and Raman spectra of, 73, 74f Coordinate analysis, with GF matrix method, 22 spectra-structure correlations of, 99e100 Correlation charts Cartesian coordinate displacements for CH3,CH2, and CH, 4, 4f for harmonic oscillator, 9, 9f development of, 4 e e for XY2 molecules, 20 22, 21f group frequency, 213 215 Cast films Coupled oscillators preparation of, 36e37 bent triatomic molecule, 64e65, 65f, 66f of starch, 119e120, 120f equal combinations, 67e68, 68f, 68t CeBr group frequencies of, 63e67, 64f, 65f, 66f, 67f group frequencies of, 108, 109t linear aliphatic systems, 65e67, 66f, 67f IR and Raman spectra of, 108, 108f, 138, 161f, 162f linear molecules, 63e64, 64f spectra-structure correlations of, 108e110, 108f, rules of thumb for, 67e70, 68f, 68t, 69f, 70f 109t unequal combinations, 70, 70f CeCl Crystallinity, in IR spectra, 57, 58f group frequencies of, 108, 109t CeSeC compounds IR and Raman spectra of, 108, 108f, 138, 161f, 162f IR and Raman spectra of, 108, 108f spectra-structure correlations of, 108e110, 108f, 109t spectra-structure correlations of, 108e110, 108f, wavenumber regions for, 11, 11t 109t Cellulose, 139, 174f CeSeSeC compounds Center of symmetry, spectroscopy and, 19, 19f IR and Raman spectra of, 108, 108f CH bend, correlation chart for, 213 spectra-structure correlations of, 108e110, 108f, CH stretch, correlation chart for, 4, 4f, 213 109t See CH2. Methylene Cyanuric acid, spectra-structure correlations of, 93, See CH3. Methyl 93f Chain length, vibrational frequency and, 66e67, 66f Cyclohexane, 135, 140f, 178f, 200 Chemometric data analysis, 118 n-Cyclohexane, IR and Raman spectra for, 80f 3-Chloro toluene, 138, 162f Cyclopropyl rings, spectra-structure correlations 1-Chloro-octane, 138, 161f of, 125 CI. See Configuration interaction method Classic harmonic oscillator, 10e11, 10f, 11t D potential energy of, 12 Data analysis techniques, for spectra interpretation, C]N compounds, IR and Raman spectra of, 137, 158f, 117 159f Deformation vibrations. See also X-H deformation CeN stretching vibrations of amines, spectra-structure correlations of, 128 correlation chart for, 215 of CO2,8,9f group frequencies of, 104e105t Fermi resonance and, 60e61, 61f IR and Raman spectra of, 103, 104f of H2O, 8, 9f spectra-structure correlations of, 103e105, 104e105t, of linear aliphatic systems, 67, 67f 104f of methyl groups, spectra-structure correlations of, CeO stretching vibrations 128e129 correlation chart for, 215 of methylene groups, spectra-structure correlations group frequencies of, 104e105t of, 128e129 IR and Raman spectra of, 103, 104f Degenerate vibrations, 22 spectra-structure correlations of, 103e105, 104e105t, Degrees of freedom 104f, 131 calculating, 8 C]O stretching vibrations, correlation chart for, 214 molecular motion and, 8e9, 9f 220 INDEX

Demountable cell, 35 force constant for, 11, 11t Density functional theory (DFT) methods, 24 IR and Raman spectra of, 135, 141f Dextrin, 187f, 203 wavenumber regions for, 11, 11t DFT. See Density functional theory methods Double bond stretch, vibrational spectrum for, 3, 3f d See Dialkyl acetylenes, spectra-structure correlations of, 85 p. Effective penetration depth Dialkyl sulfates, spectra-structure correlations of, DRIFTS. See Diffuse Reflectance Infrared Fourier 110e111, 110f, 111e112t Transform Spectroscopy Diamond, for IR transmission, 32, 33t Diatomic molecule E See Cartesian coordinate displacements for, 9, 9f Eel. Electronic energy d as classic harmonic oscillator, 10e11, 10f Effective penetration depth ( p), in attenuated total classical vibrational frequency for, 10 reflectance, 41 dipole moments of, 14e15, 14f Electric fields potential energy of, 12, 12f dipole moments and, 14e15, 14f wavenumber regions for, 11, 11t in electromagnetic radiation, 7, 7f Dibasic phosphate, spectra-structure correlations in Raman scattering, 15e18, 15f, 18f of, 130 Electromagnetic radiation, 7e8, 7f, 8f Dibasic sodium phosphate, 139, 169f absorption of, 7e8, 8f n-Dibutyl amine, 137, 157f parameters of, 7, 7f n-Dibutyl ether, 137, 155f in Raman scattering, 15, 17e18, 18f n -Dibutyl phosphite, 138, 166f Electronic energy (Eel), 8 Diethylene glycol, 137, 155f Empirical characteristic frequencies, for vibrational Diffraction grating, in dispersive systems, 27e28, 28f spectroscopy interpretation, 2e3, 3f Diffuse Reflectance Infrared Fourier Transform Empirical force fields Spectroscopy (DRIFTS), 41e43 in coordinate analysis, 22 Dimethyl carbonate, 136, 145f in GF matrix method, 23 Dimethyl formamide, 136, 152f for molecular force field, 23 Dimethyl malonate, 136, 146f Energy. See also Potential energy 2,4-Dimethyl pentane, 178f, 200 anharmonic oscillator and, 13 Dimethyl siloxane polymer, 183f, 202 photon absorption and, 7e8, 8f Dimethyl sulfoxide, 138, 163f Environmental dependence, of vibrational spectra, Dimethyl terephthalate, 136, 146f 55e62 1,3-Dimethyl urea, 136, 150f Fermi resonance, 60e62, 61f, 62t 2,5-Dimethyl-1,5-hexadiene, 179f, 200 hydrogen bonding, 57e60, 59f Di-n-butyl amine, 195f, 208e209 solid, liquid, gaseous states, 55e57, 56f, 57f, 58f Dioctyl phthalate, 192f, 206 Epichlorohydrin, 137, 156f 1,4-Dioxane, 184f, 202 Epoxy rings, spectra-structure correlations 2-(4,6eDiphenyle1,3,5etriazinee2eyl)e5 alkyloxy of, 125 phenol, hydrogen bonding in, 60 1,2-Epoxypentane, 186f, 203 See Dipole moment Erot. Rotational energy amplitude modulation of, 18, 18f Esters, IR and Raman spectra of, 136, 145f, 146f, 147f, in IR absorption, 14e15, 14f 148f, 149f in Raman scattering, 15e16, 15f Ethers vibrational amplitude and, 15 group frequencies of, 104e105t Dispersive Raman instrumentation, 28e29, 29f IR and Raman spectra of, 137, 155f, 156f Dispersive systems, 27e28, 28f spectra-structure correlations of, 103e105, 104e105t, Dissociation limit, anharmonic oscillator and, 13 104f 2,6-Di-t-butyl phenol, 137, 155f n-Ethyl acetamide, 196f, 209 Dodecyl sulfate, 138, 164f Ethyl carbamate, 136, 152f Double bond Ethyl cellulose, 139, 175f correlation chart for, 214 Ethyl methyl sulfide, 189f, 204 cumulated, spectra-structure correlations of, 80e81t, Ethylenes, spectra-structure correlations of, 132 See 85e86, 86f, 126 Evib. Vibrational energy INDEX 221

F Gaussian-type orbitals (GTO), in STO-3G basis set, 24 Far-infrared (Far-IR) spectroscopy, frequencies of, GF matrix method, coordinate analysis with, 13e14 e See 22 23 Far-IR spectroscopy. Far-infrared spectroscopy a-D-Glucose, 193f, 207e208 Fermi resonance Glycine, 136, 149f e idealized, 60 61, 61f Glycolic acid, 136, 147f selected groups and, 62t Groove spacing, in dispersive systems, 27, 28f e vibrational spectra and, 60 62, 61f Group frequencies Fluorinated alkane groups, spectra-structure of alcohols and ethers, 104e105t correlations of, 130 of boron compounds, 110, 111e112t Fluorine compounds, IR and Raman spectra of, 138, of carbonyl groups, 100t 161f, 162f factors that effect, 99f, 101e103 3-Fluoro toluene, 138, 162f correlation charts of, 213e215 Fluorolube, FT-IR spectrum of, 38f coupled oscillators, 63e67, 64f, 65f, 66f, 67f 3-Fluorotoluene, 190f, 205 of halogen compounds, 108, 109t Force constant (K) of inorganic compounds, 112, 113t for bond types, 11, 11t of nitrogen containing compounds, 105, 106e107t in classical harmonic oscillator, 10 origin of, 63e71 in GF matrix method, 23 oscillator combination rules of thumb, 67e70, 68f, 68t, stretching frequencies and, 102 69f, 70f Fractional linear calibration equations, 47e48 of phosphorus compounds, 110, 111e112t Frequency of silicon compounds, 110, 111e112t of electromagnetic radiation, 7, 7f of sulfur compounds, 110, 111e112t in IR absorption, 14 X-H stretching group, 73e74, 74f in IR and Raman vibrational bands, 2 Group Theory of photons, 7, 7f e symmetry and, 18 vibrational, classical, 10 11, 10f for vibrational spectroscopy interpretation, 2e3, 3f FT-IR calibration plot GTO. See Gaussian-type orbitals for AMD-AETAC copolymers, 49, 52f of PAM-AETAC samples, 49, 52f H FT-IR spectroscopy H . See Hydrogen e 2 interferometer for, 30 32, 31f H O. See Water e 2 of PAM-AETAC samples, 48, 49 50f Halogen-carbon stretch, spectra-structure correlations e ratio method for, 46 47 of, 132e133 FT-Raman calibration plot Hammet constant, methylene group correlation with, for AMD-AETAC copolymers, 52, 52f 84e85, 85f of PAM-AETAC samples, 52, 52f Harmonic oscillator FT-Raman spectroscopy Cartesian coordinate displacements for, 9, 9f e interferometer for, 30 32, 31f classic, 10e11, 10f, 11t e of PAM-AETAC samples, 48, 49 50f potential energy of, 12, 12f, 13f ratio method for, 47 quantum mechanical, 12e13, 12f, 13f Fundamental transitions, harmonic and anharmonic Hartree-Fock (HF) method, 24 oscillators and, 13 Heisenberg’s uncertainty principle, harmonic Fundamental vibrational spectrum, 3, 3f oscillator and, 12f, 13 Furans Heptane, 135, 140f e in-plane vibrations of, 96, 97 98t n-Heptane Furans, spectra-structure correlations of, 96e99, IR and Raman spectra for, 80f 97e98t, 97f, 125 IR spectroscopy v. Raman spectroscopy, 118f, 119 G cis-3-Heptene, 135, 141f trans-3-Heptene, 135, 141f Gaseous state, environmental dependence of e Hetero-aromatic rings, spectra-structure correlations vibrational spectra in, 55 57, 56f, 57f of, 128 222 INDEX

Heterocyclic aromatic five-membered rings, spectra- analyte concentration and, 45e46 structure correlations of, 96e99, 97e98t, 97f application of, 1 Heterocyclic aromatic six-membered rings, spectra- center of symmetry and, 19, 19f structure correlations of, 93e99, 93f dispersive systems for, 27e28, 28f pyridines, 94, 95t, 96t historical perspective on, 3e4 triazines and melamines, 94e96 instrument development for, 4 Heteronuclear diatomic molecule, dipole moments interpretation of, 2, 117e133 of, 14 Raman spectroscopy v., 1e2, 2t, 118f, 119 1-Hexadecanol symmetry and, 18 IR and Raman spectra of, 137, 154f tools for, 117e119, 118f IR spectroscopy v. Raman spectroscopy, 118f, 119 transmission, 34e39 n-Hexane, IR and Raman spectra for, 80f Infrared (IR) transmitting materials, 32, 33t 1-Hexane sulfonic acid sodium salt, 192f, 207 Inorganic compounds 2-Hexanone, 188f, 204 IR and Raman spectra of, 138e139, 167f, 168f, 169f, 1-Hexene, 135, 141f 170f, 171f 2-Hexyne, 181f, 201 spectra-structure correlations of, 112, 113t HF. See Hartree-Fock method In-phase stretch Homonuclear diatomic molecule, dipole moments of bent triatomic molecule, 64e65, 65f, 66f of, 14 of CO2,8,9f Hydrogen (H2), center of symmetry of, 19, 19f Fermi resonance and, 61, 61f Hydrogen bonding of H2O, 8, 9f in acidic proton vibrational frequencies, 126 of linear molecules, 63e64, 64f in amino and hydroxy stretching vibrations, 124 In-plane vibrations environmental dependence of vibrational spectra of olefinic groups, 82, 83f and, 57e60, 59f of pyridines, 94, 95t intramolecular, 59e60 of pyrroles, furans, and thiophenes, 96, 97e98t 4-Hydroxy benzaldehyde, 136, 147f Instrumentation, 27e32 Hydroxy (OH) group dispersive Raman instrumentation, 28e29, 29f environmental dependence of vibrational spectra dispersive systems, 27e28, 28f and, 58, 60f interferometric spectrometers, 30e32, 31f IR and Raman spectra of, 73, 74f Raman spectroscopy sample arrangements, 29, 30f spectra-structure correlations of, 124e125, 133 for spectra interpretation, 117 2-Hydroxy-4-(methoxy)-benzophenone, hydrogen Intensity bonding in, 60 in IR and Raman vibrational bands, 2 Hydroxypropylmethyl cellulose, 139, 175f of Raman scattering, 17, 46 2-Hydroxypyridine, spectra-structure correlations of, wavenumber v., 14 93, 93f Interaction effects, in carbonyl groups, 103 Interferometric spectrometers, 30e32, 31f I Internal reflectance, in attenuated total reflectance, Identification, spectral databases and interpretation 40, 40f for, 118 Internal reflection element (IRE), in attenuated total 2-Imidazolidinethione, 138, 165f reflectance, 39 2-Imidazolidone, 136, 151f Interpersonal skills, for spectra interpretation, 117 Imino compounds, spectra-structure correlations Intramolecular hydrogen bonding, 59e60 of, 127 IR absorption process. See Infrared absorption process Impurities, identifying, 123 IR gas phase contours. See Infrared gas phase contours Infrared (IR) absorption process, 13e15, 14f IR spectroscopy. See Infrared spectroscopy dipole moment in, 14e15, 14f IR transmitting materials. See Infrared transmitting frequencies in, 13e14 materials See Infrared (IR) gas phase contours, of CO2, 55, 56f IRE. Internal reflection element Infrared (IR) spectroscopy. See also FT-IR spectroscopy; Isoamyl nitrate, 137, 159f Mid-infrared spectroscopy; Near-infrared Isobutyl amine, 137, 156f spectroscopy Isocyanuric acid, hydrogen bonding in, 59 INDEX 223

Isooctane, 135, 140f Methylene (CH2) bend, correlation chart for, 213 Isopropyl alcohol, 136, 153f Methylene (CH2) groups Isopropyl nitrate, 137, 160f deformation vibrations of, spectra-structure Isoquinolines, spectra-structure correlations of, 128 correlations of, 128e129 Isotactic polyethylene, 139, 171f Hammet constant correlation with, 84e85, 85f spectra-structure correlations of, 74e75, 76t, 77f, K 125e126 K See . Force constant Methylene (CH2) stretch, correlation chart for, 4, 4f, 213 KBr disc 4-Methyl-imidazole, 199f, 211e212 preparation of, 38, 39f 4-Methyl-pyridine-3-boronic acid, 197f, 210 KBr windows, in IR transmission, 32, 33t Michelson interferometer, 30e31, 31f Ketones, stretching vibration for, 101 Microscopy, 43e44 KRS-5, in IR transmission, 32, 33t reflection IR, 44 Kubelka-Munk equation, in DRIFTS, 41e43 transmission IR, 43e44 Mid-infrared (Mid-IR) spectroscopy L application of, 1 Lactones, spectra-structure correlations of, 126e127 frequencies of, 13e14 Lambert-Beer law Raman spectroscopy v., 1e2, 2t in absorption spectroscopy, 14 Mid-IR. See Mid-infrared spectroscopy in attenuated total reflectance, 41 Mirror, in Michelson interferometer, 30e31, 31f in quantitative analysis, 45e46 Molecular force field, 23 Linear molecules Molecular geometry, in GF matrix method, 22 in-phase stretch of, 63e64, 64f Molecular motion molecular motions for, 8, 9f degrees of freedom and, 8e9, 9f out-of-phase stretch of, 63e64, 64f of linear molecules, 8, 9f Liquids of non-linear molecules, 8, 9f environmental dependence of vibrational spectra in, Molecular vibrational kinetic energy, in GF matrix 55e57 method, 22 preparation for, 35e36 Møller Plessant perturbation (MP2) method, 24 Monobasic phosphate, spectra-structure correlations M of, 130 Magnetic fields, in electromagnetic radiation, 7 MP2. See Møller Plessant perturbation method Maleic anhydride, 136, 147f Multi-configuration self-consistent field (MCSF) MCSF. See Multi-configuration self-consistent field method, 24 method Melamines, 199f, 212 N spectra-structure correlations of, 94e96 NaCl windows, in IR transmission, 32, 33t Melts, preparation of, 38e39 Napthalenes, spectra-structure correlations of, 92, 93t Mesomeric effects, in carbonyl groups, 102e103 Near-infrared (Near-IR) spectroscopy Meta (3) chlorophenol, 187f, 203 application of, 1 Metal oxides, spectra-structure correlations of, 133 frequencies of, 13e14 Meta-tolyl boronic acid, 138, 161f Raman spectroscopy v., 1e2, 2t Methane sulfonic acid, 138, 163f Near-IR. See Near-infrared spectroscopy Methanol, 136, 153f Newton’s second law, with GF matrix method, 23 Methoxy group, spectra-structure correlations of, 126 NH group. See Amino group Methyl (CH3) bend, correlation chart for, 213 NH2 group Methyl (CH3) groups IR and Raman spectra of, 73, 74f deformation vibrations of, spectra-structure spectra-structure correlations of, 133 correlations of, 128e129 Nitrates spectra-structure correlations of, 75, 76t, 78f, in-phase stretching of, 19, 20f 125e126 organic, spectra-structure correlations of, 127 1-Methyl naphthalene, 180f, 200 spectra-structure correlations of, 129 Methyl (CH3) stretch, correlation chart for, 4, 4f, 213 Nitrites, organic, spectra-structure correlations of, 127 224 INDEX

Nitrogen containing compounds diffuse reflectance of, 53, 53f group frequencies of, 105, 106e107t FT-IR calibration plot of, 49, 52f IR and Raman spectra of, 105, 106f FT-Raman calibration plot of, 52, 52f spectra-structure correlations of, 105e108, 106e107t, quantitative analysis of, 48e53 106f spectra of, 48, 49e50f 2-Nitropropane, 137, 160f Paper, 185f, 203 Nitroso groups, spectra-structure correlations of, 127 PE. See Potential energy N]O compounds n-Pentane, IR and Raman spectra for, 80f group frequencies of, 105, 106e107t PH stretch, spectra-structure correlations of, 126 IR and Raman spectra of, 105, 106f, 137, 159f, 160f Phenol, 137, 154f spectra-structure correlations of, 105e108, 106e107t, Phenyl acetate, 191f, 205e206 106f Phenyl boronic acid, 198f, 210e211 N-O stretching vibrations, correlation chart for, 215 Phosphate, spectra-structure correlations of, 130 Non-linear molecules, molecular motions for, 8, 9f Phosphine oxide. See also P]O Non-polar groups, Raman spectroscopy for, 1 Phosphine oxide, spectra-structure correlations of, Nujol Mull 110f, 111e112t FT-IR spectrum with, 34, 35f, 38f Phosphoric acids, spectra-structure correlations preparation of, 37, 38f of, 126 of starch, 119e120, 120f Phosphorus compounds, IR and Raman spectra of, Nylon, 6, 6, 139, 173f 138, 165f, 166f Phosphorus ester, spectra-structure correlations of, O 110f, 111e112t n-Octane, IR and Raman spectra for, 80f Photon energy, parameters of, 7 1-Octyne, 135, 142f Photon frequency, parameters of, 7, 7f OH group. See Hydroxy group Photons, 7 Olefinic compounds absorption of, 7e8, 8f correlation chart for, 214 parameters of, 7, 7f spectra-structure correlations of, 127, 131e132 in Raman scattering, 16e17, 16f Olefinic groups Pipenidindione dioxime, 137, 159f in-plane vibrations of, 82, 83f P]O compounds out-of-plane vibrations of, 84, 84f correlation chart for, 215 Olefinic groups, spectra-structure correlations of, group frequencies of, 110, 111e112t 82e85, 82f, 83f, 84f, 85f, 125 IR and Raman spectra of, 110, 110f Oleic acid, 136, 148f spectra-structure correlations of, 110e112, 130 Out-of-phase stretch PeO containing compounds, spectra-structure of bent triatomic molecule, 64e65, 65f, 66f correlations of, 131 of CO2,8,9f Polar groups, IR spectroscopy for, 1 e of H2O, 8, 9f Polarizability, in Raman scattering, 15 16, 16f, 18, 18f of linear aliphatic systems, 66e67, 66f Poly acrylamide (PAM) of linear groups, 68e69, 69f band assignments for, 48, 50e51t of linear molecules, 63e64, 64f diffuse reflectance of, 53, 53f Out-of-plane vibrations FT-IR calibration plot of, 49, 52f of olefinic groups, 84, 84f FT-Raman calibration plot of, 52, 52f of pyridines, 94, 96t IR and Raman spectra of, 139, 176f Overtones, anharmonic oscillators and, 13 quantitative analysis of, 48e53 spectra of, 48, 49e50f P Poly acrylic acid, 139, 173f Palmitic acid, IR spectroscopy v. Raman spectroscopy, Poly-2-(acryloyloxy)-Ethyltrimethyl Ammonium 118f, 119 Chloride (AETAC) Palmitic acid, 136, 148f band assignments for, 48, 50e51t PAM. See Poly acrylamide diffuse reflectance of, 53, 53f PAM-AETAC FT-IR calibration plot of, 49, 52f band assignments for, 48, 50e51t FT-Raman calibration plot of, 52, 52f INDEX 225

IR and Raman spectra of, 139, 176f historical perspective on, 3e4 quantitative analysis of, 48e53 interpretation of, 2, 117e133 spectra of, 48, 49e50f IR spectroscopy v., 1e2, 2t, 118f, 119 Polybutadiene, 139, 171f sample arrangements for, 29, 30f Polyethylene oxide, 139, 172f symmetry and, 18 Polymers, IR and Raman spectra of, 139, 171f, 172f, tools for, 117e119, 118f 173f, 174f, 175f, 176f Ratio method, 46e48 Polystyrene, 194f, 208 fractional linear calibration equations for, 47e48 Polytetrafluoroethylene, 139, 172f Rayleigh light filters, 28e29, 29f Polyvinyl alcohol, 139, 172f Rayleigh scattering Polyvinyl pyrrolidone, 139, 173f classical description of, 17e18, 18f Potassium nitrate, 139, 168f dispersive Raman instrumentation and, 28e29, 29f Potential energy (PE) oscillating dipoles in, 15 of anharmonic oscillator, 13, 13f process of, 16, 16f of harmonic oscillator, 12, 12f, 13f Reflected radiation, 33 Primary amine salts, spectra-structure correlations Reflection IR, 39e43 of, 126 ATR, 39e41, 40f, 42t 2-Propanethiol, 189f, 204e205 DRIFTS, 41e43 Pyridines microscopy with, 44 in-plane vibrations of, 94, 95t Refractive index IR and Raman spectra of, 136, 144f angle of incidence and, 33, 34f out-of-plane vibrations of, 94, 96t for attenuated total reflectance, 40e41, 40f spectra-structure correlations of, 94, 95t, 96t, 128 Ring vibrations, of benzene, 89, 90f Pyrimidines, spectra-structure correlations of, 128 Rotational energy (Erot), 8 Pyrroles 3n-5 Rule-of-thumb, 8, 9f in-plane vibrations of, 96, 97e98t 3n-6 Rule-of-thumb, 8, 9f Pyrroles, spectra-structure correlations of, 96e99, 97e98t, 97f, 125 S Sample preparation, 33e34, 34f, 35f Q for attenuated total reflectance, 39 Quantitative analysis, 44e53 of cast films, 36e37 analyte concentration and, 45e46 issues with, 119e121, 120f examples of, 48e53 for liquids, 35e36 of PAM-AETAC samples, 48e53 of melts, 38e39 ratio method, 46e48 of solid-powdered samples, 37e38, 38f, 39f Quantum mechanical harmonic oscillator, 12e13, 13f Sampling methods, 32e44 potential energy of, 12, 12f IR transmitting materials, 32, 33t Quantum mechanical method, for molecular force microscopy, 43e44 field, 23 reflection IR, 39e43 Quantum mechanics, vibrational energy in, 12 ATR, 39e41, 40f, 42t Quinazolines, spectra-structure correlations of, 128 DRIFTS, 41e43 Quinolines, spectra-structure correlations of, 128 techniques for, 33e34, 34f, 35f, 119e121, 120f transmission IR, 34e39 R cast films, 36e37 Raman scattering liquids and solutions, 35e36 center of symmetry and, 19, 19f melts, 38e39 classical description of, 17e18, 18f solid-powdered samples, 37e38, 38f, 39f intensity of, 17, 46 Scattered radiation, 33 process of, 15e17, 15f, 16f Sealed amalgam cell, 36 Raman spectroscopy. See also FT-Raman spectroscopy SH stretch, spectra-structure correlations of, 126 analyte concentration and, 45e46 Signal-to-noise ratio (SNR), array detector and, 29 application of, 1 SiH stretch, spectra-structure correlations of, 126 dispersive Raman instrumentation for, 28e29, 29f Silica gel, 139, 170f 226 INDEX

Silicon dioxide, 183f, 202 hierarchy of quality of, 121e122 Siloxane compounds, IR and Raman spectra of, 138, Specular reflectance, with microscopy, 44 166f Spurious bands, sample preparation and, 121 Siloxane polymer, 138e139, 166f, 175f Starch Single bond IR and Raman spectra of, 34, 35f, 139, 174f force constant for, 11, 11t sample preparation of, 119, 120f wavenumber regions for, 11, 11t Stearic acid, 136, 149f Single bond stretch, vibrational spectrum for, 3, 3f STO. See Slater-type orbital SieO containing compounds STO-3G basis set, 24 correlation chart for, 215 Stokes Raman scattering, 16f, 17 group frequencies of, 110, 111e112t classical description of, 17e18, 18f IR and Raman spectra of, 110, 110f Stretch. See Double bond stretch; In-phase stretch; spectra-structure correlations of, 110e112, 131 Out-of-phase stretch; Single bond stretch; Triple Six-membered rings, stretching waves for, 70, 70f bond stretch Slater-type orbital (STO), in STO-3G basis set, 24 Stretching frequencies SNR. See Signal-to-noise ratio bond angle and, 101e102 S]O compounds force constant and, 102 correlation chart for, 215 Stretching vibration group frequencies of, 110, 111e112t for aldehydes, 101 IR and Raman spectra of, 110, 110f of carbonyl groups, 101e103 spectra-structure correlations of, 110e112 CeO, spectra-structure correlations of, 131 Sodium acetate, 188f, 204 Fermi resonance and, 60e61, 61f Sodium bicarbonate, 139, 168f hydrogen bonding in, 124e125 Sodium carbonate, 139, 168f for ketone, 101 Sodium carboxymethyl cellulose, 139, 174f of six-membered rings, 70, 70f Sodium di-isobutyl dithiophosphate, 138, 166f Stretch-stretch interaction, group frequencies of, Sodium isopropyl xanthate, 138, 164f 63e64, 64f Sodium molybdate, 139, 170f Structural verification, spectral databases and Sodium perchlorate, 139, 170f interpretation for, 118 Sodium sulfate, 138, 167f Structure correlations, with spectra, 124e133 À Sodium sulfite, 138, 167f 800-200 cm 1, 133 À Software tools, for spectral interpretation, 122e123 850-480 cm 1, 132e133 À Solid state, environmental dependence of vibrational 900-500 cm 1, 133 À spectra in, 55e57, 58f 900-700 cm 1, 132 À Solid-powdered samples, preparation of, 37e38, 1000-600 cm 1, 131e132 À 38f, 39f 1280-830 cm 1, 131 À Solutions, preparation for, 35e36 1300-750 cm 1, 131 À Solvents, identifying, 123 1350-1000 cm 1, 130 À1 Sox compounds, spectra-structure correlations of, 1350-1080 cm , 130 À 129e130 1400-900 cm 1, 129e130 À Spectral databases, for identification and structural 1480-1310 cm 1, 129 À verification, 118 1500-1250 cm 1, 128e129 À Spectral database tools 1620-1420 cm 1, 128 À computer-based, 122e123 1660-1450 cm 1, 127 À for spectra interpretation, 117 1660-1500 cm 1, 128 À Spectral interpretation, 121e124 1690-1400 cm 1, 127 À computer-based libraries and software tools for, 1900-1550 cm 1, 126e127 À 122e123 2300-1900 cm 1, 126 À examine the spectrum, 123e124 2600-2100 cm 1, 126 À problem definition, 123 3000-2700 cm 1, 125e126 À spectral reference library hierarchy of quality, 121e122 3100-2400 cm 1, 126 À Spectral reference libraries 3200-2980 cm 1, 125 À computer-based, 122e123 3700-3100 cm 1, 124e125 INDEX 227

Sulfanamides, spectra-structure correlations of, of melts, 38e39 129e130 microscopy with, 43e44 Sulfates of solid-powdered samples, 37e38, 38f, 39f in-phase stretching of, 19, 20f Transmitted radiation, 33 spectra-structure correlations of, 129e130 Triazines, spectra-structure correlations of, 94e96 Sulﬁnic acids, spectra-structure correlations of, 129e130 Triazine species, spectra-structure correlations of, 128 Sulfonamides, spectra-structure correlations of, 110f, Tribasic sodium phosphate, 139, 169f 111e112t n-Tributyl amine, 137, 157f Sulfonates, spectra-structure correlations of, 110f, Tributyl borate, 197f, 210 111e112t Tributyl phosphite, 138, 165f Sulfones, spectra-structure correlations of, 110e111, 2,4,6-Trichlorobenzoyl chloride, 191f, 206 110f, 111e112t, 129e130 Trimethyl amine, 137, 158f Sulfonic acids, spectra-structure correlations of, 110f, Trimethyl isocyanurate, 136, 151f 111e112t, 129e130 Triphenyl phosphine, 138, 165f Sulfonic acid salts, spectra-structure correlations of, Triphenyl phosphine oxide, 196f, 209e210 110f, 111e112t, 129e130 Triple bond Sulfonyl chlorides, spectra-structure correlations of, correlation chart for, 214 110f, 111e112t force constant for, 11, 11t Sulfonyl halides, spectra-structure correlations of, IR and Raman spectra of, 135, 142f 129e130 spectra-structure correlations of, 80e81t, 85e86, Sulfoxide. See also S]O 86f, 126 Sulfoxides, spectra-structure correlations of, 110e111, wavenumber regions for, 11, 11t 110f, 111e112t, 129e130 Triple bond stretch, vibrational spectrum for, 3, 3f Sulfur compounds, IR and Raman spectra of, 138, 163f, 1,3,5-Trisubstituted benzene, in-phase stretching of, 164f, 165f 20, 20f Symmetric vibrations, Raman spectroscopy for, 1 Symmetry U center of, 18e19, 19f Ureas, IR and Raman spectra of, 136, 149f, 150f, 151f, 152f Group Theory and, 18 of in-phase stretch of linear molecules, 64, 64f V IR and Raman active vibrations, 18e22, 19f, 20f, 21f Vibrating mechanical molecular models, 3 of XY2 bent molecule, 20, 20f Vibrational amplitude, dipole moment and, 15 Vibrational energy (Evib), 8 T in quantum mechanics, 12 Talc, 139, 171f Vibrational frequency Taylor series, for GF matrix method, 23 for bent triatomic molecule, 64e65, 65f, 66f 4-Tert-butyltoluene, 179f, 200 classical, 10e11, 10f Tetrahydrofuran, 137, 156f, 184f, 202 for linear aliphatic systems, 66e67, 66f, 67f Tetramethyl ammonium chloride, 137, 158f for linear molecules, 63e64, 64f m-Tetramethyl xylene diisocyanate, 136, 144f Vibrational quantum number, anharmonic oscillator Thiocarbonyl compounds, spectra-structure and, 13 correlations of, 129e130 Vibrational spectroscopy Thiophenes advantages of, 45 in-plane vibrations of, 96, 97e98t application of, 1 Thiophenes, spectra-structure correlations of, 96e99, calculating, 22e24 97e98t, 97f environmental dependence of, 55e62 Toluene, 136, 143f Fermi resonance, 60e62, 61f, 62t para-Toluene sulfonic acid hydrate, 138, 163f hydrogen bonding, 57e60, 59f Trans, trans-2,4-hexadien-1-ol, 186f, 203 solid, liquid, gaseous states, 55e57, 56f, 57f, 58f Trans-2-hexen-1-ol, 182f, 201 interpretation of, 2 Transmission IR, 34e39 techniques for, 1 of cast ﬁlms, 36e37 Vibrational spectrum, 3, 3f of liquids and solutions, 35e36 Vinyl groups, spectra-structure correlations of, 132 228 INDEX

W X-H stretching group, IR and Raman spectra of, 73e74, 74f Water (H 2O), fundamental vibrations for, 8, 9f wavenumber regions for, 11, 11t Wavelength, of electromagnetic radiation, 7, 7f XY2 bent molecule Wavenumbers e e Cartesian coordinate displacements, 20 22, 21f in classical harmonic oscillator, 10 11 symmetry of, 20, 20f of electromagnetic radiation, 7, 7f XY v 2 type identical oscillators, 68, 68f, 68t intensity ., 14 Xylenes, 136, 143f Wavenumber regions, for diatomic oscillator groups, 11, 11t Z X Zero point energy, 12 Zinc dimethyl dithiocarbamate, 138, 164f X-axis scale, for sample preparation, 34, 121 ZnSe X-H deformation, vibrational spectrum for, 3, 3f FT-IR spectrum with, 34, 35f X-H stretch in IR transmission, 32, 33t correlation chart for, 213 vibrational spectrum for, 3, 3f