A general preference for gauche alkyl–phenyl interactions. The use of lanthanide shift reagents in determining the preferred conformations of some alkyl 1-phenylethyl sulphoxides

Abstract

The conformations of alkyl threo- and erythro-1-phenylethyl sulphoxides have been studied by means of n.m.r. spectroscopy, largely by the computer simulation of the lanthanide-induced shifts. It has been demonstrated that, in the most populated conformation, the achiral alkyl group is oriented gauche to the phenyl and anti to the methyl group, irrespective of the nature of the alkyl group (Me, Et, Prⁱ, or Bu^t) and irrespective of the configuration of the sulphoxide. A considerable contribution from a second stable rotamer is suggested for the lower alkyl homologues (Me, Et, or Prⁱ), whereby the alkyl group is flanked by the phenyl and methyl groups.