1H and 13C NMR studies on 1,3,2‐dioxarsolanes

Abstract

AbstractThe 1H and 13C NMR spectra of a series of 1,3,2‐dioxarsolanes have been obtained at 2.1 T and some at 9.4 T. The chemical shifts and spin‐spin coupling constants have been obtained from complete spectral analyses of the 1H and proton‐coupled 13C spectra. The spectral data are interpreted on the basis of two rapidly interconverting half‐chair conformers with a pseudoaxial substituent at arsenic. Unique assignment of syn/anti or cis/trans geometries have been made from 1H or 13C NMR spectroscopy alone. The syn and trans isomers of the 4‐methyl‐ and 4,5‐dimethyl‐1,3,2‐dioxarsolanes, respectively, appear to be conformationally biased towards the forms with pseudoequatorial methyl groups. The general trends in the geminal and vicinal 1H1H and 13C1H coupling constants are interpreted in terms of stereospecific, electronegativity and lone‐pair effects of the oxygen heteroatoms and conformational factors. The NMR data on the 1,3,2‐dioxarsolanes are discussed with reference to related 1,3‐dithoxa‐ and 1,3‐dithia‐ five‐membered rings with As, P, S or C at the 2‐position.