The N-(1-phenylethyl)dithiocarbamate anion. Electronic transitions, ultraviolet and CD spectra, and reversible formation of its ammonium salts

Abstract

The UV and CD spectra of tetrabutylammonium (S)-N-(1-phenylethyl)dithiocarbamate (3c) have been recorded in acetonitrile and in absolute ethanol. In the dithiocarbamate anion, the sulfur lone pairs are expected to interact to give a low-energy symmetric combination (n₊) and an antisymmetric combination (n_–) with the higher energy. The UV spectrum was interpreted with the aid of CNDO/S calculations, and the CD spectrum with calculations by the Schellman matrix method. The CD spectrum contains a medium-strong positive band at 230 nm, which lacks a counterpart in the UV spectrum and was initially tentatively assigned to the n₊→π₁* transition. However, the theoretical calculations predict a negative sign for this band, and consequently no assignment for the 230 nm band can be given at present.

Except for the 230 nm band, the calculations predict correct signs and qualitatively correct intensities for the CD bands between 200 and 400 nm in a narrow range of orientations of the 1-phenylethyl group with respect to the dithiocarbamate ion, and it is expected that the favoured conformation falls in this conformational range.

Similar studies of (S)-(1-phenylethyl)ammonium (S)-N-(1-phenylethyl)dithiocarbamate (3a) and triethylammonium (S)-N-(1-phenylethyl)dithiocarbamate (3b) failed because these salts decompose in solution with ultimate formation of carbon disulfide. This decomposition has been studied by UV spectroscopy, and a mechanism has been proposed.