S.T.E.T.Women's College, Mannargudi Semester Iii Ii M
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Chapter 12 Lecture Notes
Chemical Kinetics “The study of speeds of reactions and the nanoscale pathways or rearrangements by which atoms and molecules are transformed to products” Chapter 13: Chemical Kinetics: Rates of Reactions © 2008 Brooks/Cole 1 © 2008 Brooks/Cole 2 Reaction Rate Reaction Rate Combustion of Fe(s) powder: © 2008 Brooks/Cole 3 © 2008 Brooks/Cole 4 Reaction Rate Reaction Rate + Change in [reactant] or [product] per unit time. Average rate of the Cv reaction can be calculated: Time, t [Cv+] Average rate + Cresol violet (Cv ; a dye) decomposes in NaOH(aq): (s) (mol / L) (mol L-1 s-1) 0.0 5.000 x 10-5 13.2 x 10-7 10.0 3.680 x 10-5 9.70 x 10-7 20.0 2.710 x 10-5 7.20 x 10-7 30.0 1.990 x 10-5 5.30 x 10-7 40.0 1.460 x 10-5 3.82 x 10-7 + - 50.0 1.078 x 10-5 Cv (aq) + OH (aq) → CvOH(aq) 2.85 x 10-7 60.0 0.793 x 10-5 -7 + + -5 1.82 x 10 change in concentration of Cv Δ [Cv ] 80.0 0.429 x 10 rate = = 0.99 x 10-7 elapsed time Δt 100.0 0.232 x 10-5 © 2008 Brooks/Cole 5 © 2008 Brooks/Cole 6 1 Reaction Rates and Stoichiometry Reaction Rates and Stoichiometry Cv+(aq) + OH-(aq) → CvOH(aq) For any general reaction: a A + b B c C + d D Stoichiometry: The overall rate of reaction is: Loss of 1 Cv+ → Gain of 1 CvOH Rate of Cv+ loss = Rate of CvOH gain 1 Δ[A] 1 Δ[B] 1 Δ[C] 1 Δ[D] Rate = − = − = + = + Another example: a Δt b Δt c Δt d Δt 2 N2O5(g) 4 NO2(g) + O2(g) Reactants decrease with time. -
Organic Chemistry
Wisebridge Learning Systems Organic Chemistry Reaction Mechanisms Pocket-Book WLS www.wisebridgelearning.com © 2006 J S Wetzel LEARNING STRATEGIES CONTENTS ● The key to building intuition is to develop the habit ALKANES of asking how each particular mechanism reflects Thermal Cracking - Pyrolysis . 1 general principles. Look for the concepts behind Combustion . 1 the chemistry to make organic chemistry more co- Free Radical Halogenation. 2 herent and rewarding. ALKENES Electrophilic Addition of HX to Alkenes . 3 ● Acid Catalyzed Hydration of Alkenes . 4 Exothermic reactions tend to follow pathways Electrophilic Addition of Halogens to Alkenes . 5 where like charges can separate or where un- Halohydrin Formation . 6 like charges can come together. When reading Free Radical Addition of HX to Alkenes . 7 organic chemistry mechanisms, keep the elec- Catalytic Hydrogenation of Alkenes. 8 tronegativities of the elements and their valence Oxidation of Alkenes to Vicinal Diols. 9 electron configurations always in your mind. Try Oxidative Cleavage of Alkenes . 10 to nterpret electron movement in terms of energy Ozonolysis of Alkenes . 10 Allylic Halogenation . 11 to make the reactions easier to understand and Oxymercuration-Demercuration . 13 remember. Hydroboration of Alkenes . 14 ALKYNES ● For MCAT preparation, pay special attention to Electrophilic Addition of HX to Alkynes . 15 Hydration of Alkynes. 15 reactions where the product hinges on regio- Free Radical Addition of HX to Alkynes . 16 and stereo-selectivity and reactions involving Electrophilic Halogenation of Alkynes. 16 resonant intermediates, which are special favor- Hydroboration of Alkynes . 17 ites of the test-writers. Catalytic Hydrogenation of Alkynes. 17 Reduction of Alkynes with Alkali Metal/Ammonia . 18 Formation and Use of Acetylide Anion Nucleophiles . -
Solvent Effects on Structure and Reaction Mechanism: a Theoretical Study of [2 + 2] Polar Cycloaddition Between Ketene and Imine
J. Phys. Chem. B 1998, 102, 7877-7881 7877 Solvent Effects on Structure and Reaction Mechanism: A Theoretical Study of [2 + 2] Polar Cycloaddition between Ketene and Imine Thanh N. Truong Henry Eyring Center for Theoretical Chemistry, Department of Chemistry, UniVersity of Utah, Salt Lake City, Utah 84112 ReceiVed: March 25, 1998; In Final Form: July 17, 1998 The effects of aqueous solvent on structures and mechanism of the [2 + 2] cycloaddition between ketene and imine were investigated by using correlated MP2 and MP4 levels of ab initio molecular orbital theory in conjunction with the dielectric continuum Generalized Conductor-like Screening Model (GCOSMO) for solvation. We found that reactions in the gas phase and in aqueous solution have very different topology on the free energy surfaces but have similar characteristic motion along the reaction coordinate. First, it involves formation of a planar trans-conformation zwitterionic complex, then a rotation of the two moieties to form the cycloaddition product. Aqueous solvent significantly stabilizes the zwitterionic complex, consequently changing the topology of the free energy surface from a gas-phase single barrier (one-step) process to a double barrier (two-step) one with a stable intermediate. Electrostatic solvent-solute interaction was found to be the dominant factor in lowering the activation energy by 4.5 kcal/mol. The present calculated results are consistent with previous experimental data. Introduction Lim and Jorgensen have also carried out free energy perturbation (FEP) theory simulations with accurate force field that includes + [2 2] cycloaddition reactions are useful synthetic routes to solute polarization effects and found even much larger solvent - formation of four-membered rings. -
Solvents and Solvent E¤Ects in Organic Chemistry
Contents 1 Introduction ......................................................... 1 2 Solute-Solvent Interactions ........................................... 7 2.1 Solutions . .......................................................... 7 2.2 Intermolecular Forces . ............................................ 12 2.2.1 Ion-Dipole Forces . ................................................. 13 2.2.2 Dipole-Dipole Forces................................................ 14 2.2.3 Dipole-Induced Dipole Forces ....................................... 15 2.2.4 Instantaneous Dipole-Induced Dipole Forces . ...................... 16 2.2.5 Hydrogen Bonding . ................................................. 17 2.2.6 Electron-Pair Donor/Electron-Pair Acceptor Interactions (EPD/EPA Interactions) . ..................................................... 23 2.2.7 Solvophobic Interactions ............................................ 31 2.3 Solvation . .......................................................... 34 2.4 Preferential Solvation................................................ 43 2.5 Micellar Solvation (Solubilization) ................................... 48 2.6 Ionization and Dissociation . ........................................ 52 3 Classification of Solvents ............................................. 65 3.1 Classification of Solvents according to Chemical Constitution ......... 65 3.2 Classification of Solvents using Physical Constants . .................. 75 3.3 Classification of Solvents in Terms of Acid-Base Behaviour. ......... 88 3.3.1 Brønsted-Lowry -
Ochem ACS Review 23 Aryl Halides
ACS Review Aryl Halides 1. Which one of the following has the weakest carbon-chlorine bond? A. I B. II C. III D. IV 2. Which compound in each of the following pairs is the most reactive to the conditions indicated? A. I and III B. I and IV C. II and III D. II and IV 3. Which of the following reacts at the fastest rate with potassium methoxide (KOCH 3) in methanol? A. fluorobenzene B. 4-nitrofluorobenzene C. 2,4-dinitrofluorobenzene D. 2,4,6-trinitrofluorobenzene 4. Which of the following reacts at the fastest rate with potassium methoxide (KOCH 3) in methanol? A. fluorobenzene B. p-nitrofluorobenzene C. p-fluorotoluene D. p-bromofluorobenzene 5. Which of the following is the kinetic rate equation for the addition-elimination mechanism of nucleophilic aromatic substitution? A. rate = k[aryl halide] B. rate = k[nucleophile] C. rate = k[aryl halide][nucleophile] D. rate = k[aryl halide][nucleophile] 2 6. Which of the following is not a resonance form of the intermediate in the nucleophilic addition of hydroxide ion to para -fluoronitrobenzene? A. I B. II C. III D. IV 7. Which chlorine is most susceptible to nucleophilic substitution with NaOCH 3 in methanol? A. #1 B. #2 C. #1 and #2 are equally susceptible D. no substitution is possible 8. What is the product of the following reaction? A. N,N-dimethylaniline B. para -chloro-N,N-dimethylaniline C. phenyllithium (C 6H5Li) D. meta -chloro-N,N-dimethylaniline 9. Which one of the reagents readily reacts with bromobenzene without heating? A. -
Bsc Chemistry
Subject Chemistry Paper No and Title 05, ORGANIC CHEMISTRY-II (REACTION MECHANISM-I) Module No and Title 15, The Neighbouring Mechanism, Neighbouring Group Participation by π and σ Bonds Module Tag CHE_P5_M15 CHEMISTRY PAPER :5, ORGANIC CHEMISTRY-II (REACTION MECHANISM-I) MODULE: 15 , The Neighbouring Mechanism, Neighbouring Group Participation by π and σ Bonds TABLE OF CONTENTS 1. Learning Outcomes 2. Introduction 3. NGP Participation 3.1 NGP by Heteroatom Lone Pairs 3.2 NGP by alkene 3.3 NGP by Cyclopropane, Cyclobutane or a Homoallyl group 3.4 NGP by an Aromatic Ring 4. Neighbouring Group Participation on SN2 Reactions 5. Neighbouring Group Participation on SN1 Reactions 6. Neighbouring Group and Rearrangement 7. Examples 8. Summary CHEMISTRY PAPER :5, ORGANIC CHEMISTRY-II (REACTION MECHANISM-I) MODULE: 15 , The Neighbouring Mechanism, Neighbouring Group Participation by π and σ Bonds 1. Learning Outcomes After studying this module, you shall be able to Know about NGP reaction Learn reaction mechanism of NGP reaction Identify stereochemistry of NGP reaction Evaluate the factors affecting the NGP reaction Analyse Phenonium ion, NGP by alkene, and NGP by heteroatom. 2. Introduction The reaction centre (carbenium centre) has direct interaction with a lone pair of electrons of an atom or with the electrons of s- or p-bond present within the parent molecule but these are not in conjugation with the reaction centre. A distinction is sometimes made between n, s and p- participation. An increase in rate due to Neighbouring Group Participation (NGP) is known as "anchimeric assistance". "Synartetic acceleration" happens to be the special case of anchimeric assistance and applies to participation by electrons binding a substituent to a carbon atom in a β- position relative to the leaving group attached to the α-carbon atom. -
23.5 Basicity and Acidity of Amines
23_BRCLoudon_pgs5-0.qxd 12/8/08 1:22 PM Page 1122 1122 CHAPTER 23 • THE CHEMISTRY OF AMINES alkylamines, this resonance occurs at rather small chemical shift—typically around d 1. In aromatic amines, this resonance is at greater chemical shift, as in the second of the preceding examples. Like the OH protons of alcohols, phenols, and carboxylic acids, the NH protons of amines under most conditions undergo rapid exchange (Secs. 13.6 and 13.7D). For this reason, split- ting between the amine N H and adjacent C H groups is usually not observed. Thus, in the NMR spectrum of diethylamine,L the N H resonanceL is a singlet rather than the triplet ex- pected from splitting by the adjacent CHL2 protons. In some amine samples, the N H resonance is broadened and, like the OL H protonL of alcohols, it can be obliterated fromL the spectrum by exchange with D2O (the “DL2O shake,” p. 611). The characteristic 13C NMR absorptions of amines are those of the a-carbons—the carbons attached directly to the nitrogen. These absorptions occur in the d 30–50 chemical-shift range. As expected from the relative electronegativities of oxygen and nitrogen, these shifts are somewhat less than the a-carbon shifts of ethers. PROBLEMS 23.4 Identify the compound that has an M 1 ion at mÜz 136 in its CI mass spectrum, an IR 1 + = absorption at 3279 cm_ , and the following NMR spectrum: d 0.91 (1H, s), d 1.07 (3H, t, J 7Hz), d 2.60 (2H, q, J 7Hz), d 3.70 (2H, s), d 7.18 (5H, apparent s). -
Reaction Kinetics in Organic Reactions
Autumn 2004 Reaction Kinetics in Organic Reactions Why are kinetic analyses important? • Consider two classic examples in asymmetric catalysis: geraniol epoxidation 5-10% Ti(O-i-C3H7)4 O DET OH * * OH + TBHP CH2Cl2 3A mol sieve OH COOH5C2 L-(+)-DET = OH COOH5C2 * OH geraniol hydrogenation OH 0.1% Ru(II)-BINAP + H2 CH3OH P(C6H5)2 (S)-BINAP = P(C6 H5)2 • In both cases, high enantioselectivities may be achieved. However, there are fundamental differences between these two reactions which kinetics can inform us about. 1 Autumn 2004 Kinetics of Asymmetric Catalytic Reactions geraniol epoxidation: • enantioselectivity is controlled primarily by the preferred mode of initial binding of the prochiral substrate and, therefore, the relative stability of intermediate species. The transition state resembles the intermediate species. Finn and Sharpless in Asymmetric Synthesis, Morrison, J.D., ed., Academic Press: New York, 1986, v. 5, p. 247. geraniol hydrogenation: • enantioselectivity may be dictated by the relative reactivity rather than the stability of the intermediate species. The transition state may not resemble the intermediate species. for example, hydrogenation of enamides using Rh+(dipamp) studied by Landis and Halpern (JACS, 1987, 109,1746) 2 Autumn 2004 Kinetics of Asymmetric Catalytic Reactions “Asymmetric catalysis is four-dimensional chemistry. Simple stereochemical scrutiny of the substrate or reagent is not enough. The high efficiency that these reactions provide can only be achieved through a combination of both an ideal three-dimensional structure (x,y,z) and suitable kinetics (t).” R. Noyori, Asymmetric Catalysis in Organic Synthesis,Wiley-Interscience: New York, 1994, p.3. “Studying the photograph of a racehorse cannot tell you how fast it can run.” J. -
Enzymatic Kinetic Isotope Effects from First-Principles Path Sampling
Article pubs.acs.org/JCTC Enzymatic Kinetic Isotope Effects from First-Principles Path Sampling Calculations Matthew J. Varga and Steven D. Schwartz* Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States *S Supporting Information ABSTRACT: In this study, we develop and test a method to determine the rate of particle transfer and kinetic isotope effects in enzymatic reactions, specifically yeast alcohol dehydrogenase (YADH), from first-principles. Transition path sampling (TPS) and normal mode centroid dynamics (CMD) are used to simulate these enzymatic reactions without knowledge of their reaction coordinates and with the inclusion of quantum effects, such as zero-point energy and tunneling, on the transferring particle. Though previous studies have used TPS to calculate reaction rate constants in various model and real systems, it has not been applied to a system as large as YADH. The calculated primary H/D kinetic isotope effect agrees with previously reported experimental results, within experimental error. The kinetic isotope effects calculated with this method correspond to the kinetic isotope effect of the transfer event itself. The results reported here show that the kinetic isotope effects calculated from first-principles, purely for barrier passage, can be used to predict experimental kinetic isotope effects in enzymatic systems. ■ INTRODUCTION staging method from the Chandler group.10 Another method that uses an energy gap formalism like QCP is a hybrid Particle transfer plays a crucial role in a breadth of enzymatic ff reactions, including hydride, hydrogen atom, electron, and quantum-classical approach of Hammes-Schi er and co-work- 1 ers, which models the transferring particle nucleus as a proton-coupled electron transfer reactions. -
Diastereoisomers As Probes for Solvent Reorganizational Effects On
Chemical Physics 324 (2006) 8–25 www.elsevier.com/locate/chemphys Diastereoisomers as probes for solvent reorganizational effects on IVCT in dinuclear ruthenium complexes Deanna M. DÕAlessandro, F. Richard Keene * Department of Chemistry, School of Pharmacy and Molecular Sciences, James Cook University, Townsville, Qld. 4811, Australia Received 19 June 2005; accepted 1 September 2005 Available online 3 October 2005 Abstract 5+ 0 0 IVCT solvatochromism studies on the meso and rac diastereoisomers of [{Ru(bpy)2}2(l-bpm)] (bpy = 2,2 -bipyridine; bpm = 2,2 - bipyrimidine) in a homologous series of nitrile solvents revealed that stereochemically directed specific solvent effects in the first solvation shell dominated the outer sphere contribution to the reorganizational energy for intramolecular electron transfer. Further, solvent pro- portion experiments in acetonitrile/propionitrile mixtures indicated that the magnitude and direction of the specific effect was dependent on the relative abilities of discrete solvent molecules to penetrate the clefts between the planes of the terminal polypyridyl ligands. In particular, the specific effects were dependent on the dimensionality of the clefts, and the number, size, orientation and location of the solvent dipoles within the interior and exterior clefts. 5+ 5+ IVCT solvatochromism studies on the diastereoisomeric forms of [{Ru(bpy)2}2(l-dbneil)] and [{Ru(pp)2}2(l-bpm)] {dbneil = dibenzoeilatin; pp = substituted derivatives of 2,20-bipyridine and 1,10-phenanthroline} revealed that the subtle and systematic changes in the nature of the clefts by the variation of the bridging ligand, and the judicious positioning of substituents on the terminal ligands, profoundly influenced the magnitude of the reorganizational energy contribution to the electron transfer barrier. -
AROMATIC NUCLEOPHILIC SUBSTITUTION-PART -2 Electrophilic Substitution
Dr. Tripti Gangwar AROMATIC NUCLEOPHILIC SUBSTITUTION-PART -2 Electrophilic substitution ◦ The aromatic ring acts as a nucleophile, and attacks an added electrophile E+ ◦ An electron-deficient carbocation intermediate is formed (the rate- determining step) which is then deprotonated to restore aromaticity ◦ electron-donating groups on the aromatic ring (such as -OH, -OCH3, and alkyl) make the reaction faster, since they help to stabilize the electron-poor carbocation intermediate ◦ Lewis acids can make electrophiles even more electron-poor (reactive), increasing the reaction rate. For example FeBr3 / Br2 allows bromination to occur at a useful rate on benzene, whereas Br2 by itself is slow). In fact, a substitution reaction does occur! (But, as you may suspect, this isn’t an electrophilic aromatic substitution reaction.) In this substitution reaction the C-Cl bond breaks, and a C-O bond forms on the same carbon. The species that attacks the ring is a nucleophile, not an electrophile The aromatic ring is electron-poor (electrophilic), not electron rich (nucleophilic) The “leaving group” is chlorine, not H+ The position where the nucleophile attacks is determined by where the leaving group is, not by electronic and steric factors (i.e. no mix of ortho– and para- products as with electrophilic aromatic substitution). In short, the roles of the aromatic ring and attacking species are reversed! The attacking species (CH3O–) is the nucleophile, and the ring is the electrophile. Since the nucleophile is the attacking species, this type of reaction has come to be known as nucleophilic aromatic substitution. n nucleophilic aromatic substitution (NAS), all the trends you learned in electrophilic aromatic substitution operate, but in reverse. -
The Automated Flow Synthesis of Fluorine Containing Organic Compounds
The automated flow synthesis of fluorine containing organic compounds by CHANTAL SCHOLTZ Submitted in partial fulfilment of the requirements for the degree PHILOSOPHAE DOCTOR In the Faculty of Natural & Agricultural Sciences UNIVERSITY OF PRETORIA PRETORIA Supervisor: Dr D.L. Riley February 2019 DECLARATION I, Chantal Scholtz declare that the thesis/dissertation, which I hereby submit for the degree PhD Chemistry at the University of Pretoria, is my own work and has not previously been submitted by me for a degree at this or any other tertiary institution. Signature :.......................................... Date :..................................... ii ACKNOWLEDGEMENTS I would herewith sincerely like to show my gratitude to the following individuals for their help, guidance and assistance throughout the duration of this project: My supervisor, Doctor Darren Riley, for his knowledge and commitment. Thank you for being a fantastic supervisor and allowing me the opportunity to learn so many valuable skills. My husband, Clinton, for all your love, support and patience and for always being there for me. You are the best. My family, for all the encouragement and support you gave me as well as always believing in me. I will always appreciate what you have done for me. Mr Drikus van der Westhuizen and Mr Johan Postma for their assistance at the Pelchem laboratories with product isolation and characterisation. Dr Mamoalosi Selepe for NMR spectroscopy services, Jeanette Strydom for XRF services and Gerda Ehlers at the UP library for her invaluable assistance. All my friends and colleagues for the continuous moral support, numerous helpful discussions and necessary coffee breaks. My colleagues at Chemical Process Technologies for their ongoing support and motivation, especially Dr Hannes Malan and Prof.