Spectral analysis of the high‐resolution proton‐coupled carbon‐13 NMR spectra of 1,3,2‐dithiarsolanes

Abstract

AbstractThe high‐resolution proton‐coupled 13C NMR spectra of 2‐chloro‐ and 2‐phenyl‐4‐methyl‐1,3,2‐dithiarsolane and 2‐chloro‐ and 2‐phenyl‐1,3,2‐dithiarsolane have been obtained and completely analysed. The spectral analysis has provided all the 13C chemical shifts and 13C1H coupling constants, including their relative signs. The results of this work are adequately interpreted in terms of two rapidly equilibrating half‐chair conformers with the 4‐methyl pseudo‐axial or pseudo‐equatorial. The cis isomers appear to be conformationally biased towards the form with the 4‐methyl pseudo‐equatorial. The two one‐bond 13C1H coupling constants of the methylene group are distinctly different. For both the cis and trans isomers, the largest one‐bond coupling always involves the methylene proton situated syn to the substituent at arsenic. The observed variation in the geminal and vicinal 13C1H coupling constants are discussed in terms of a stereospecific inductive effect of the sulphur hetero‐atoms and conformational factors.