1H and 13C NMR Studies on 1,3,2-Dioxarsolanes

Article abstract of DOI:10.1002/omr.1270210704

The 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 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-dioxarsolenes, 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-dioxa- and 1,3-dithia- five-membered rings with As, P, S, or C at the 2-position.