INFRARED AND RAMAN SPECTRA AND THE NORMAL VIBRATIONS OP METHXTjENECYCLO PRO PANE DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By EDMUND J • BLAU » B • Chexu*) S • M* The Ohio State University 1953 Approved by : TABLE OF CONTENTS Pago LIST OF FIGURES ill LIST OF TABLES iv ACKNOWLEDGEMENT viii I INTRODUCTION 1 II SYNTHESIS AND IDENTIFICATION OF METHYIT*;BCYCLOPrtOFANE 6 III EXPERIMENTAL WORK 12 1. Preparation and Purification of Mothylonocyclo- propane 12 (a) Chlorination of Kethallyl Chloride 12 (b) Ring Closure with Magnesium and Tetra- hydrofuran 15> 2. Infrared Spectra 19 3» Raman Spectra 29 (a) Spectrograph and Accessory A > )ai'atu3 29 (b) The Raman Tube 29 (c) Polarization Measurements 3 (d) Wave Length Measurements 33 (e) Results of Raman Measurements 3^ IV GENERAL DISCUSSION OF T'TE STRUCTURE AMD VIBRATIONS OF METHYLENECYC LOPRO PANE k 2 1. Theory of Strained Rings and the Configuration of I-ie thy le no cyclopropane l'r?. 2. Structural Parameters )}.Q 3. Moments of Inertia and Band Typo 3 plj. U* Symmetry Classification and Selection Rules for the Ilethylenecycloprooane Vibrations 5*7 3. Qualitative Discussion of the Forms of Vibrations 70 V NORMAL COORDINATE CALCULATION 77 1. Introduction 77 2. Definition of Coordinates Cl 3. Outline of Normal Coordinate Theory 05> ij.* The s-Vectore for the Valence Coordinates 92 b* Symmetry Coordinates and the S-Vectors 99 6 . Elimination of Redundancies 112 7* Wilson*s G-Matrix 121 - I - \ 01.004 TABLE OP CONTENTS (Continued) Page V NORMAL COORDINATE CALCULATION (Cont'd) 8 . General Discussion of the Potential Energy Matrices 130 9. The Valence Force Constants and F-llatrix 137 (a) Ethylenic Force Constants 11\.2 (b) Methylenlc Force Constants II4.8 (c) Ring Force Constants llj.8 10. Force Constant Matrix, 3S for the Symmetry Coordinates 1$U- 11. The Solution of the Characteristic nations and the Form of the Normal Coordinates 166 VI ASSIGNMENT OF FREQUENCIES 183 1. Ring Stretching Mode lBij. 2. Ring Deformation Modes i Q j 3. Double-Bond Stretching Mode 193 I4.. Double-Bond Bending Modes 201+ 5* Ethylenic CHg Bending Modes 206 6 . Methylenlc CH2 Bending Modes 211|. 7» CH Stretching Modes 219 8 * Summary and Conclusions 227 9* Addendum: BIcyclobutane Structure 233 APPENDIX I - HybrldizatIon of Orbitals at the Junction of a Double Bond and a Ring 23^ APPENDIX II - Derivation of the Redundancy Conditions for Ring Closure 239 AUTOBIOGRAPHY ?1\3 - ii - LIST OP FIGURES Pago 1. Infrared Spectrum of Methylenecyclopropane rrom 1 to 1£> Microns 21 2.Infrared Spectrum of Methylenecyclopropane from 3.2 to 3-5 Microns 22 3* Infrared Spectrum of lie thylenecycloprooane from 1.6 to 2.5 Microns 23 1*.. Raman Spectrum of Methylenecyclopropane 38 5. Configuration of Methylenecyclopropane 14-9 6 .Methylene cyclopropane Vibrations: Skeletal Modes 73 7. Methylenecyclopropane Vibrations: Modes of the Ethylenic CH£ Group 7^ 8. Methylenecyclopropane Vibrations: Stretching Modes of the Methylenlc CH2 Groups 75 9. Methylenecyclopropane Vibrations: Bending Modes of the Methylenlc CH2 Groups 76 10 . Valence Coordinates and Unit Vectors of Methylenecyclopropane 83 - iii - LIST OF TABLES Page 1 . Infrared Spectrum of Hethylenecycloprooane 2lv 2. Raman Displacements of Hethylenecyclopropane 39 , 3. Equilibrium Bond Length.3 and Bond Anglos of Methylenecyclopropane 53 It- Coordinates of the Atoms of Methylonecyclopro mne 5U- 5. Character Table for the Point Group C ^ v and Total Characters for Dipole Moment, PolarizabllIty, and’ Vibrational Degrees of Freedom of Hethylenecyclo­ propane 61 6 . Reduction of Characters for Vibrational Degrees of Freedom, Dipole Moment, and PolarizabIIity of Methylenecyclopropane 62 7. Optical Activity and Classification of Vibra-ional Modes of Methylenecyclopropane 66 8.Symmetry Types of Binary Combinations and Overtones for the Point Group C2v 89 9. Valence Coordinates of Methylenecyclopropane 82 1 0 ,Unit Vectors Directed Along the Bonds of Methylene­ cyclopropane In Terms of the Orthogonal Unit Vectors a, b, and c 86 11. 3-Vectors for the Valence Coordinates of Methylene­ cyclopropane in Toms of the Orthogonal Unit Vectors a, b, and c 96 12. Symmetry Coordinates of Methylenecyclopropane 102 13. Hedefir d Symmetry Coordinates 105 XJ [■ • S-Vectors for the Symmetry Coordinates of Methyl­ enecyclopropane In Terms of the Orthogonal Unit Vectors a, b, and c 108 15. Final P o m of Ai Symmetry Coordinates of Methylenecyclopropane 118 - lv - LIST OP TABLES (Part 2) Pag© 16. Pinal Forms of Symmetry Coordinates of Methylenecy c lo propane 119 17. Final Forms of Ag Symmetry Coordinates of Methylenecyclopropane 120 18. Pinal Forms of B2 Symmetry Coordinates of Methylenecyclopropane 120 19. ^-Matrix for *1 Modes 125 20. ^-Matrix for Bl Modes 126 21. ^-Matrix for a 2 Modes 127 22. ^-Matrix for b 2 Modes 128 23. ^-Matrix for Al Modes with CH Stretchings Split Off 131 2 k . ^-Matrix for B1 Modes with CH Stretchings Split Off 132 25. Matrix for a2 Modes with CII Stretching ,Split Off 133 26. ^-Matrix for b 2 Modes with CH Stretching Split Off I3lv 27. Definitions of Elementary Force Constants for Methylenecyclopropane 151 28. Numerical Values of Methylenecyclopropane Force Constants 1p 3 29. /-Matrix for A1 Modes 157 30. /-Matrix for B1 Mode s 1 $ B 31. /-Matrix for A2 Modes 159 32. /-Matrix for b 2 Modes 160 33- Numerical Form of /-Matrix for Ai Modes (CH Stretchings Omitted) 161 3l|-• Numerical Form of /-Matrix for Modes (CH Stretchings Omitted) 161 35. Numerical Porm of /-Matrix for A2 Modes (CH Stretching Omitted) 162 - v - LIST OP TABLES (Part 3) Pag© 36. Numerical Form of ^-Matrix for B2 Modes (CH Stretching Omitted) 162 37. Roots of the Secular Equation for Ai Modes 169 3 8 . Roots of the Secular Equation for 13^ Modes 170 39. Roots of the Secular Equation for A2 Modes 171 I4.O. Roots of the Secular Equation for B2 Modes 171 l+l. Roots of the Aj_ Secular Equation in the Diagonal Approximation 173 1^2. Roots of the B^ Secular Equation in the Diagonal Approximat ion 17 3 lt3. Roots of the Ag Secular Equation in the Diagonal Approximat ion 17i+ Lflj.. Roots of the B2 Secular Equation in the Diagonal Approximation 1 7 I4. I4.5 . Transformation from Symmetry Coordinates to Normal Modes for Symmetry Type A^ 176 1+6. Transformation from Symmetry Coordinates to Normal Modes for Symmetry 'Type B]_ 176 Ij.7. Transformation from Symmetry Coordinates to Normal Modes for Symmetry Type A2 177 1+8. Transformation from Symmetry Coordinates to Normal Modes for Symmetry Type Bp 177 1+9 • Distribution of Potential Energy among the Symmetry Modes for the Al Normal Modes 181 50. Distribution of Potential Energy among the Symmetry Modes for the Normal Modes 181 $1. Distribution of Potential Energy among the Symmetry Modes for the A2 Normal Modes 182 5>2. Distribution of Potential Energy among the Symmetry Modes for the B2 Normal Modes 182 53- CharacteristIc Frequencies (in of the Infrared and Raman Spectra of Asymmetrically Disubstituted Ethylene s 191+ - vi - LIST OP TABLES (Part Ij.) Page 5U* Classification of CH Stretching Modes of Methylenecyclopropane 220 55 • Correspondences Between the Methylenlc CH Stretching Modes of Methylenecyclonropane and Spiropentane 222 56* Observed CH Stretching Frequencies of Snironentane 223 - vii - ACKNOWL3DGEI-IENT The author wishes to express his deep appreciation to Professor William J. Taylor, who suggested this problem and has guided the work throughout its course. The debt which this work In its present form owes to Professor Taylor*s generosity In both time and advice cannot be adequately expressed. Thanks are also due to Professor C.3. Boord, and to Drs. K.W. Greenlee and J.M. Derfer, for the use of their facilities and their knowledge of organic chemistry In the preparation of the material used in this InvestigatIon. - viii - I. BTTROOTCTION This Investigation is the first in a projected program in t&ich a coordinated study will be made of the vibrational spectra, thermodynamic properties, and molecular structure of molecules containing strained rings. The existence of strain­ ed rings and their effects on the properties of molecules containing them has long been a subject of interest and spec­ ulation for the organic chemist. In recent years our under­ standing of these compounds has been increased greatly by the application of modern physical and physico-chemical tech­ niques: the determination of bond lengths and angles by electron and x-ray diffraction; the study of vibrational and electronic spectra, and recently of pure rotational (micro­ wave) spectra; the study of the energy associated with ring closure and ring strain by precise thermochemical measure­ ments ; etc. The methods of the quantum theory of valence have also been applied to the nature of the bonds in strained rings, and quite recently there has been a revival of in­ terest In this direction with ttj^ introduction of the concept of "bent" bonds, as will be discussed in some detail sub­ sequently. A great deal remains to be done, however, before it can be considered that we have a thorough understanding of this class of compounds. For only a relatively small number of - 2 - compounds (e.g., cyclopropane, cyclobutane, cyclopentane, ■ spiropentane, ethylene oxide, etc.) have reasonably complete and coordinated studies of the thermodynamic properties, vi­ brational spebtra, and molecular structure been carried out. Even for these the assignments of vibrational frequencies can­ not be considered final, and may have to be modified when related molecules, e.g., the substituted derivatives, are studied in more detail. In the present program it is planned to study these and similar molecules, and their derivatives, principally through studies of their vibrational (Raman and infrared absorption) speotra, and their thermodynamic properties (low temperature heat capacities and "third-law" entropies, and gas heat capacities).