1312
COMMUNICATION TO THE EDITOR
by Coggeshall13 and is confirmed by the present work. Other workers have reported differences between the spectra of nitrobenzene and aniline and the spectrum of the complex at 8300 to 12000 cm.-’, the region of the overtones of the NH and CH stretching bands.3 Our investigation of the 1:1 complex also disclosed differences between the spectra of aniline and of the complex in the NH stretching region from 3200 to 3450 cm.-l but the observed shift of the two free NHz stretching bands, 15 cm.-l to higher frequencies, in the spectrum of the complex are attributable merely to the solvent action of nitrobenzene. The same shifts of the free NHz bands were observed for solutions of aniline in carbon disulfide. Intensities of the NH bands are decreased by nitrobenzene, indicating that nitrobenzene produces some dissociation of intermolecular hydrogen bonds of aniline; weak hydrogen bonding between nitrobenzene and aniline is not apparent, but cannot be ruled out. Carbon disulfide produces a greater diminution of aniline N H band iiitensities than does nitrobenzene. Intensities of other aniline bands in the spectrum of the complex showed the following: (a) except for the NH bands, all bands show intensity enhancement of from 0 to 25%; (b) the largest increased intensities are %yo for the 1500 cm.-l band and 20% for the 692 cm.-l band. Except for the ’ (13) N. D. Coggeshall, footnote 10 in article by Landauer and McConnell, J . Am. Chem. Soc., 74, 1221 (1952).
Vol. 62
NH bands, the same or slightly greater enhancement of intensities was shown by the spectrum of aniline in carbon disulfide. A small shift in band position was found for the 880 cm.-l band of aniline, which shifts to 879 cm.-l in the iiitrobeiizene complex. In carbon disulfide this band shifts to 878 cm.-l. Another very small shift, 2 cm.-l to higher frequency, occurs for the unsymmetrical band of nitrobeiixeiie a t 703 cm. - l in the presence of aniline. Also, the band becomes symmetrical. The same changes occur for nitrobenzene in carbon disulfide. Small intensity changes found for nitrobenzene in the complex are: (a) most of the absorption bands showed changes; some were enhanced and some were diminished; (b) the largest enhancements were found for the symmetrical and unsymmetrical NOz stretching modes, 1347 and 1527 cm.-l, with increases of 15 and 25%) respectively; (c) the intensity of the 703 cm.-l band increased by 10%; (d) the largest diminution of intensity, 20%, was found for the 793 cm. -1 band. Substitution of carbon disulfide for aniline produces coiisiderably more enhancement of intensities; no bands of nitrobenzene in carbon disulfide showed diminution of intensities. Differences between the effects of aniline and carbon disulfide on nitrobenzene appear to be attributable to differing solvent effects. Spectral measurements by Leonard Shufler and John Queiser and purification of compounds hy Stanley Laiiger are gratefully acknowledged.
COMMUNICATION TO THE EDITOR T H E OPTICAL ACTIVITY O F COPPER HELICES
Sir: A recent publication by Tinoco and Freeman1 coiicerning the optical activity of oriented copper helices contains a misinterpretation of an important paragraph which appears in an earlier paper by Winkler.2 Both papers dealt with an extension of E(. F. Liiidman’s early work on the apparent optical activity of dissymetric systems of conductors. Tinoco and Freeman stated that “Winkler attempted to repeat this [Lindinan’s] work and claimed that the optical rotation observed (1) L. Tinoco and M. P. Freeman, J . Phgs. Chem., 61, 1196 (1057). (2) M. H. Winkler, ibid.,60, 1656 (1956).
by Lindman was due to anisotropic scattering and not to optical activity.” An exchange of correspondence with the latter authors has established that that claim was not intended. The sentence in the paper by Winkler which states that “the observed effects were due to diffraction” refers oiily to changes in intensity. No reference to optical activity was intended then. The logical consistency of the paper was somewhat dependent on the assumption) under which the paper was written, that the helices used were optically active. PROTEIN FOUNDATION, INC. MARVINH. WINKLER 281 SOUTHSTREET PLAIN 30, MASS. JAMAICA RECEIVED JULY 28, 1958
r
c
