Hindered rotation in dithiocarbamoyl compounds by NMR measurements : Alkylation of sulfur compounds by trialkyloxonium ions

Abstract

The alkylation of methyl N,N-dialkyldithiocarbamates, of tetramethyl thiuram disulfide, and of bismethylthio-N-methylformimine has been shown to lead to the same symmetrical dithiocarbamidium salt resulting from alkylation on the thione sulfur atom. The NMR spectrum of the dithiocarbamidium ion showed approximately equal distribution of charge in the ion, resulting in a downfield shift of 0·20 to 0·50 ppm for the protons on carbon attached to nitrogen or sulfur. Its cyclic analog, 2-dimethylamino-1,3-dithiolenium ion, showed that its charge was about equally distributed, with downfield shifts of 0·40 to 0·60 ppm for the protons on carbon attached to nitrogen or sulfur when compared to 2-methylimino-1,3-dithiolane. Hindered rotation was observed around the CN bond of methyl N,N-dialkyldithio-carbamates at ambient temperature (about 37°) by NMR, but none was observed in the corresponding thiuram disulfides at ambient temperature.