CONTRIBUTION TO THE INFRARED SPECTRA OF ORGANOSULPHUR COMPOUNDS

Infrared spectra of various types of organosulphur compounds have been examined and group frequencies arising from G—S, S—S, N—S, O—S, and C=S stretching vibrations have been assigned and discussed. The C—S bands of thioketals and S—S bands of tri- and tetra-sulphides show splittings due to vibrational coupling. The O—S and N—S stretching frequencies are found around 890 and 820 cm−1 respectively, values which are much higher than the C—S stretching frequencies. Potassium alkyl xanthates exhibit the asymmetric and symmetric stretching frequencies of the CS2− ion. The splitting of C—O and C=S stretching bands in dialkyl dixanthogens have been interpreted in terms of the Fermi interaction with the combination tone of C—S and S—S stretching vibrations and with the overtone of S—S stretching vibrations respectively. The relative intensity of the C=S stretching bands in a few derivatives show marked dependence on the electronegativities of the elements directly linked to the thiocarbonyl group. It is found that the earlier assignments of the "[Formula: see text] bands" due to mixed vibrations in thioamide type derivatives have been found to be well justified on the basis of the recent normal coordinate treatment. Another band tentatively designated as the "[Formula: see text] IV band" has been assigned for these derivatives in the region 850–680 cm−1. Examination of the spectra of a number of thioamide type derivatives has shown no evidence for the presence of thiol tautomers. All of them exist as thiones exhibiting characteristic N—H absorption and "[Formula: see text] bands".