J. zyxwvutsrqp Am. Chem. Soc. zyxwvu 1980, zyxwvut 102, 5449-5453 5449 Our suggestion is that an analogous experimental study, with the cytochrome P450 enzymes, be carried out. The possible problems involved are brought out in a recent study using a model iron-porphine system, with iodosylbenzene as the oxygen ~ o u r c e . ~ Epoxidation of cis-stilbene proceeds with 82% yield to give the cis epoxide, while trans-stilbene is almost completely unreactive. The drastic difference in reactivity is easily ascribable to steric constraints at the catalytic site: which would also hinder internal rotation in a biradical intermediate if a radical mechanism is involved. The strategy we suggest is as follows: Steric factors might be minimized if one could find an olefinic substrate whose cis and trans isomers show similar reactivity toward P450 epoxidation. If one could also reasonably expect that internal rotation in a possible biradical intermediate would not be drastically hindered, such a substrate would provide an acceptable probe of mechanism. We are currently engaged in further exploration of some of the questions raised in the present study, through modeling the hy- droxylation and epoxidation of propene by oxene. Using the methods outlined here, in conjunction with theoretical evaluation of vibrational partition functions and thermodynamic activation parameters,21 we hope to more rigorously address the reactivi- ty-selectivity problem mentioned above. The allyl and vinyl carbons of propene, for example, represent extremes of reactivity in both ionic and radical reactions. Also, the unsymmetrical environment about the double bond is expected to affect the epoxidation mechanisms, in that two biradical intermediates are possible with, we expect, unequal stabilities. Acknowledgments. The authors wish to thank Dr. Andrew Komornicki for making his programs, SIGMA, FORCE, and OFTMO, available to them, and James Ferrell and Dr. Stanley Burt for many helpful discussions. They also gratefully acknowledge the financial support provided for this work by National Institute of General Medicine Grant GM27943-01 and National Cancer Institute Contract NCI 1-CP75928. Vibrational Optical Activity in Para-Substituted 1 -Methylcyclohex- 1 -enes Prasad L. Polavarapu, Max Diem, and Laurence A. Nafie*’ Contribution from the Department of Chemistry, Syracuse Uniuersity, Syracuse, New York 13210. Received January 10, 1980 Abstract: We report Raman optical activity (ROA) between 1300 and 1500 cm-’ and vibrational circular dichroism (VCD) between 2800 and 3000 cm-l for (+)-p-menth-1-eneand (+)-p-menth-l-en-9-01. The ROA data were obtained from a newly constructed spectrometer, the details of which are described. In addition, we have measured the VCD of (+)-limonene in the CH stretching region which complements the ROA spectrum of (-)-limonene available in the literature. All three molecules have the same ring structure and differ only at the para position. Since the vibrational optical activity (VOA) of these molecules in the regions selected is strongly similar we conclude that, contrary to general expectation, degenerate methyl modes do not make dominant contributions here. Instead, ring methylene modes are implicated as the major source of VOA intensity. It is encouraging that both VCD and ROA reinforce this spectral interpretation and therefore each other. This study of VOA is the first in which new spectral data for both VCD and ROA are presented. I. Introduction Current research in vibrational optical activity (VOA) has revealed considerable potential for exploring molecular stereo- ~hemistry.~-~ Recently, correlations between observed Raman optical activity (ROA) and stereochemical details in two series of related molecules have been Similar correlations have been noted in the vibrational circular dichroism (VCD) of amino acid^,^,^ peptides,I0 sugars,]’ and several organic mole- ~~~~ ~ ~~~~ ~~ (1) Alfred P. Sloan Foundation Fellow. (2) L. D. Barron, zyxwvutsrqpo Adu. Infrared Raman Spectrosc., (1978). (3) L. D. Baron in “Optical Activity and Chiral Discrimination”, S. F. (4) P. J. Stephens and R. Clark in ref 3, p 263. (5) L. A. Nafie and M. Diem, Arc. Chem. Res., 12, 296 (1979). (6) L. D. Barron and B. P. Clark, J. Chem. SOC., Perkin Trans. 2, 1164 (7) zyxwvutsrqponm L. D. Barron and B. P. Clark, J. Chem. SOC., Perkin Trans. 2, 1171 (8) M. Diem, P. J. Gotkin, J. M. Kupfer, A. P. Tindall, and L. A. Nafie, (9) M. Diem, E. Photos, H. Khouri, and L. A. Nafie, J. Am. Chem. SOC., (10) M. Diem, P. J. Gotkin, J. M. Kupfer, and L. A. Nafie, J. Am. zyxwvutsrqpo Chem. Mason, Ed., D. Reidel Dordrecht, Holland, 1979, p 219. (1979). (1979). J. Am. Chem. SOC., 99, 8103 (1977). 101, 6829 (1979). Soc., 100, 5644 (1978). c~les.’~-’~ In this paper we present VOA spectra for three closely related cyclohexene molecules which differ -only by their sub- stituent at the para position. This study is unique in that new experimental data for both VCD and ROA are presented. The combined results are then used to interpret the stereochemical origin of the major spectral features. Our approach here is to study VCD and ROA in closely related spectral regions which permits reinforcing interpretations of the data. This circumvents the general problem of lack of overlap between the usual spectral regions of VCD and ROA, although improvements in instru- mentationI6-l8 in the near future should reduce this problem by (11) C. Marcott, H. A. Havel, J. Overend, and A. Moscowitz, J. Am. (12) H. Sugeta, C. Marcott, T. R. Faulkner, J. Overend, and A. Mos- (13) T. A. Keiderling and P. J. Stephens, J. Am. Chem. SOC., 99, 8061 (14) C. Marcott, C. C. Blackburn, T. R. Faulkner, A. Moscowitz, and J. (15) T. A. Keidering and P. J. Stephens, J. Am. Chem. SOC., 101, 1396 (16) L. A. Nafie, M. Diem, and D. W. Vidrine, J. Am. Chem. SOC., 101, (17) H. Boucher, T. R. Brocki, M. Moskovits, and B. Bosnich, J. Am. Chem. Soc., 100, 7088 (1978). cowitz, Chem. Phys. Lett., 40, 397 (1976). (1977). Overend, J. Am. Chem. SOC., 100, 5262 (1978). (1979). 496 (1979). Chem. SOC., 99, 6870 (1977). 0002-7863/80/1502-5449$01.00/0 0 1980 American Chemical Society