1832
Communications to the Editor spectively.
(33)D B. Boyd, J. Am. Chem. Soc., 94,8799 (1972). (34)L. Schotte, Ark. Kern., 8,579 (1956). (35)A. Hordvik, Q. Rep. Sulfur Chem., 5, 21 (1970). (36)H. Sugeta, Spectrochim. Acta, Part A, 31, 1729 (1975). (37)T. Ottersen, L. G. Warner, and K. Seff, Acta Crystallogr.,Sect. 5, 29,2954 (1973). (38)T. Ottersen, L. G. Warner, and K. Seff, lnorg. Chem., 13, 1904 (1974). (39)See ref 5 for a summary of these.
(40)R. B. Martin, J. Phys. Chem., 78,855 (1974). (41)S.Marumo and R. W. Curtis, Phytochemistry, I, 245 (1961). (42)M. Ptak, Biopolymers, 12, 1575 (1973). (43)M. Bodanszky and G. L. Stahl, Proc. Natl. Acad. Sci. U.S.A., 71, 2791 (1974). (44)N. T. Yu, B. H.Jo, R. C. C. Chang, and J. D. Huber, Arch. Biochem. Biophys., 160.61411974\ (45)H.E: Van Wart, H. A. Scheraga, and R. B. Martin, J. Phys. Chem., 80, 1832 (1976).
COMMUNICATIONS TO THE EDITOR
Agreement Concerning the Nature of the Variation of Disulfide Stretching Frequencies with Disulfide Dihedral Angles
Sir: From the analysis of Raman and infrared data in the S-S stretching region of a series of disulfides, Bastian and Martin found, previously, that ". . . a strong Raman band, identifiable as a S-S stretching frequency, occurs uncorrelated with (disulfide) dihedral angle in the range of 496-511 cm-l in almost all cases. . . ." Subsequent to this work, and from the analysis of similar Raman data, Van Wart et a1.2 reported an approximately linear decrease in the S-S stretching frequency, u(S-S), as the CS-SC dihedral angle, x(CS-SC), was reduced from near 90° to near 0'. Shortly thereafter, Martin3 reevaluated the available experimental data and reaffirmed his original view that the values of v(S-S) are nearly invariant to
x(CS-SC). Since Martin's report3 appeared, a reinvestigation of the dependence of the values of v(S-S) on the conformation about the C-S and S-S bonds of disulfides containing the C ~ C ~ S S C a Cmoiety, a using both t h e ~ r e t i c a land ~ , ~ experim e n t a F 8 techniques has been carried out by Van Wart et al.4-8 From a study of the Raman spectra of more than two dozen strained and three dozen unstrained disulfides, previously unconsidered effects of (1)substitution at the p carbon of the CaCpSSCpCa moiety and of (2) crystal field perturbations on the values of v(S-S) obtained from crystalline compounds have been identified, and the effects of strain in the S-S bond on v(S-S) have been reevaluated8 in the light of these new ideas. As a result, the differences in interpretation
The Journal of Physical Chemistry, Vol. 80, No. 16, 1976
between the earlier studies of Bastian and MartinlJ and Van Wart et a1.2 have been resolved. The reviseds and originally proposed2 relationships between v(S-S) and x(CS-SC) are shown in Figure 4 of ref 8. The reader is referred to ref 8 for the details of the revision. The major feature of the newer correlation is the reduction in the values of v(S-S) from about 520 to 510 cm-' for 1 x(CS-SC) I values in the 65-85' range. This means that, for values of I x(CS-SC) I in the 65-85" range, v(S-S) is almost invariant to x(CS-SC), in agreement with the findings of Martin;3 however, between 0 and 65O, u(S-S) does vary with x(CS-SC), as originally proposed by Van Wart et a1.2
References and Notes (1)E. J. Bastian, Jr., and R . B. Martin, J. Phys. Chem., 77, 1129 (1973). (2)H. E. Van Wart, A. Lewis, H. A. Scheraga, and F. D. Saeva, Roc. Natl. Acad. Sci. U.S.A., 70,2619 (1973). (3)R. B. Martin, J. Phys. Chem., 78,855 (1974). (4)H.E. Van Wart, L. L. Shipman, and H.A. Scheraga, J. Phys. Chem., 78, 1848 (1974). (5)H.E. Van Wart, L. L. Shipman, and H. A. Scheraga, J. Phys. Chem., 79,1428 (1975). (6)H.E. Van Wart, F. Cardinaux, and H. A. Scheraga, J. Phys. Chem., 80,625 (1976). (7) H. E. Van Wart and H.A. Scheraga, J. Phys. Chem., 80, 1812 (1976). (8) H. E. Van Wart and H.A. Scheraga, J. Phys. Chem., 80, 1823 (1976).
Department of Chemistry Cornel1 University Ithaca, New York 14853
H. E. Van Wart H. A. Scheraga' R. Bruce Martin
Chemistry Department University of Virginia Charlottesville, Virginia 2290 1 Received December
I, 1975
