I I 72-15,275 RAWN, John David, 19»t4- PROBLEMS IN KINETICS AND CONFORMATIONAL ANALYSIS. The Ohio State University, Ph.D., 1971 Chemistry, organic University Microfilms, A XEROX Company, Ann Arbor, Michigan THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED PROBLEMS IN KINETICS AND CONFORMATIONAL ANALYSIS DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of the Ohio State University By John David Raim, B.S*, M.Sc. The Ohio State University 1971 Approved by Adviser Department of Chemistry PLEASE NOTE: Some pages have indistinct print. Filmed as received. University Microfilms, A Xerox Education Company DEDICATION To Margie Et lux in tenebris lucet ii ACKNOWLEDGMENT The author wishes to express his gratitude to Dr. Robert Ouellette for his patience during the course of this work. Few indeed are the men who combine his skill in research with superlative teaching ability. ill VITA January 12,191*-**-.... Born- Columbus,Ohio 1 9 6 6............... B.S., Capital University, Columbus,Ohio 1 9 6 7 -1 9 6.......... 9 Teaching Assistant, Department of Chemistry, The Ohio State University,Columbus,Ohio 1 9 6 9............... M.Sc., The Ohio State University, Columbus, Ohio 1 9 6 9 -1 9 7.......... 1 Research Assistant, Department of Chemistry, The Ohio State University, Columbus, Ohio FIELDS OF STUDY Major Field; Organic Chemistry Studies in Organic Chemistry. Professor H. Shechter, J. HIne, P. Gassman, G. Fraenkel, L. Paquette, D. Horton, and R. Ouellette Studies in Physical Chemistry. Professor L* Dorftaan Studies in Inorganic Chemistry. Professor H. Wilson iv TABLE OP CONTENTS page DEDICATION.................................................. ii ACKNOWLEDGMENT................................................ iii VITA................... *..................................... iv LIST OF TABLES........................ *....... vi LIST OP FIGURES............................................. vii CHAPTER I. THE CONFORMATIONAL PREFERENCE OF THE METHYL GROUP... 1 IN BICYCLIC HYDROCARBONS Introduction Results and Discussion II. OXIDATION OF TRANS-FROPENYLBENZENE WITH SODIUM 58 PALLADIUM CHLORIDE Introduction Product Studies Kinetic Studies III. EXPERIMENTAL ...................................... 65 APPENDIX.................................................... 82 REFERENCES.................................................. 90 TABLES Table Page 1. Conformational Free Energies of Substituents in Cyclohexane............................. k 2. Bond Lengths and Bond Angles in Bicyclo[2.2.1]heptane. 6 5. Equilibrium Constants for Bicyclic Compounds......... 10 U-. Thermodynamic Parameters of Bicyclic Compounds....... 10 5- Bond Lengths and Bond Angles in Bicyclo[5-2 .l3°ctane.. 14 6. Calculated Strain Energies of Bicyclic Hydrocarbons... 17 7. Relative Enthalpies of Bicyclo[x-y.z]octanes.......... IB 8. Strain Energies in Methyl. Substituted BicycloC^.2.13- heptanes in Kcal/mole............................... 25 9- Experimental Equilibrium Constants and Corresponding Free Energy and Enthalpy Differences in Kcal/mole 25 10. Equilibrium Constants and Free Energies in Kcal/mole for n -Met hylb i cyclo [5*2. lloctane s................... 52 11. Effect of Substituents in the Oxidation of trans- Propenylbenzene..................................... 12. Equilibrium Constants of Possible Pd(ll) Species...... 59 15- Least Squares Parameters for Approximation [ClJ^ax+b.. 6l l1*. Summary of Rate Constants for Reactive Species Considered. .................. .................... 65 15* Integrated Rate Laws for Other Reactive Species.. 8 7 vi FIGURES Figures Page I. Chair-Chair Interconversion of a Monosubstituted Cyclohexane....................................... 5 2 * Bicyclo£2 .2 .l]heptane.............................. 5 3* Bicyclo£? .2. lloctane.... *.......................... 11 Chair-Boat Interconversion in Bicyclo[3 -2■ lloctane.. 12 5 . Bicyclo£2.2.2 loctane............................... 15 6. Cjjiqthy 1 2-^3 Bond Angles in exo and endo-2-Methyl- bicyclo£2 .2 .l^heptane ........................ 2 6 '■'methyl-^ 5-C3 Bond Angles in Diexo and Diendo Compounds......................................... 27 8. Relative Enthalpies of Methylcyclohexanes and 2- Methylbicyclol[3 .2 .l3octanes....................... 33 9- Possible Conformations of 3-Methylbicyclo[3*2 •13- octane ................ 3^ 10- Conformations of cis and trans-1,2-Dimethylcyclo- pentane........................................... 3° 11. Rearrangement of pi Complex to Sigma-Bonded Intermediate...................................... 12. Decomposition of Sigma-Bonded Intermediate to Product........................ ^1 13. Substituent Effects in the Oxidation of trans- Propenylbenzene .................................. 50 vii CHAPTER I CONFORMATIONAL PREFERENCE OF THE METHYL GROUP IN BICYCLIC HYDROCAREONS Introduction Conformational analysis of cyclohexane and its derivatives is a li2>3 well documented subject. However, data on bicyclic systems which incorporate the cyclohexane ring in one form or another is somewhat less abundant. The systems to be discussed here are bicyclo£2.2.13- heptane, bicyclot3 -2 .l3octane, and bicyclo£2 .2 .2 ^octane, whose skeletons provide interesting extensions of the cyclohexane molecule. Comparison of the Bicyclic and Cyclohexane Systems Cyclohexane is known to exist in two readily interconvertible forms: the so-called chair and boat conformations. The difference in energy between the two conformations is approximately 5*3 Kcal/mole,the 4 chair form being the more stable. The chair forms are converted into 1. E. L. Eliel, "Stereochemistry of Carbon Compounds,” McGraw- Hill Book Co., Inc., New York, N. Y-, 1 9 6 2. 2. M. Hanack, "Conformational Theory," Academic Press, Inc., New York, N. Y .,1965• 3- E. L. Eliel, N. A. Allinger, S. J. Angyal, and G. A. Morrison, "Conformational Analysis", Interscience Publishers, Inc., New York, N. Y.,1965* b. J. B. Hendrickson, J. Amer. Chem. Soc., 8 3, **537 1 each other by internal rotation. In the process of chair conversion all equatorial bonds become axial and all axial bonds become 5 equatorial. At room temperature chair inversion occurs very rapidly. A monosubstituted cyclohexane may exist either in the chair con­ formation having the substituent axial, or in the one having it equatorial. The barrier for monosubstituted cyclohexanes is of the same order of magnitude as in cyclohexane itself. Therefore the rate of interconversion is still very rapid. However, by sufficiently cooling a monosubstituted cyclohexane the rate of interconversion is slowed to such an extent that the equatorial and axial hydrogens may Q be clearly differentiated by nuclear magnetic resonance experiments. For a substituent larger than hydrogen the distance from the C-l axial position to the syn-axial hydrogens at C-3 and C-5 is less than the distance from the C-l equatorial hydrogens at C-2 and C-6. (For example, if the axial substituent is carbon the former distance is ° ° 2.55 A and the latter is 2.8 A.) Hence an axial substituent will experience a larger van der Waals repulsion from the syn-axial 3 and 5 hydrogens than an equatorial substituent will experience from the equatorial protons at C-2 and C-6. Thus, a monosubstituted cyclohexane is more stable in the conformation in which the substituent is equatorial than in the conformation in which the substituent is axial. The equilibrium constant, K, for axial-equatorial 5* A. J. Berlin and F. R. Jensen, Chem, Ind. (London) ,126.0, 9 8 8* 6. F. R. Jensen, D. S. Noyce, C. H. Sederholm, and A. J. Berlin, J. Amer. Chem. Soc., 3 8 6 (1962). 3 interconversion will be greater than one (Fig. l). X Fig. 1 Chair-chair Interconversion of a Mono­ substituted Cyclohexane The interaction between the axial substituent and the syn- axial hydrogens in cyclohexane derivatives is the same type as that encountered in the gauche conformation of butane. For example, in methylcyclohexane there are two syn-axial methyl-hydrogen inter­ actions. Therefore the enthalpy difference between the equatorial and axial conformations should be twice the gauche-anti enthaply 7 difference in butane (0.8-0.9 Kcal/mole). This is in good agreement with the experimentally observed values. o The negative free energy difference,AGX , corresponding to the conformational equilibrium constants for a large number of sub­ stituents have been determined. The free energy differences relevant to this discussion are given in Table 1. The conformational free energy values obtained in the series of monosubstituted cyclohexanes all assume that the cyclohexane ring exists in an "ideal" chair foiTn. However, the ring in the case of poly- 7* R* A. Bonham and L- S. Bartell, J. Amer. Chem. Soc., 8l, 5^91(1959)* Table 1. Conformational Free Energies of Substituents in Cyclohexane 0 0 Group dGx { Kcal/mole) Temp C CO2 CH3 a 1 .2 25 N0S a 1 .1 100 CH3 b 1-75-1-95 2 5 -3 0 0 CN c 0 .1 25 OH b 0.7 a. R. J. Ouellette and G- E. Booth, J. Org. Chem., 3l>5l+6 (1966) . b. see ref. 3» PP- Mn-4^2. c. see ref. 3 , p. Ml-. substituted cyclohexanes may undergo various distortions from ideal s chair or boat forms. It thus seems likely that even monosubstituted cyclohexanes may be distorted from ideal chair forms particularly when the substituent in question has a large steric bulk. If this is indeed the case, then a more rigid skeleton where the magnitude of such distortions should be smaller might provide a more suitable model for the evaluation of non-bonded interactions. One such system is