A nuclear magnetic resonance study of the conformational equilibrium in fluorosulphonylethanes

Abstract

The dependence of the coupling constants on the temperature has been studied for fluorosulphonylethanes (I)–(IV) and with the aid of some simplifying assumptions quantitative information on the population of rotamers (a)–(c) has been obtained. In each case the conformation having the bulkiest substiuents in the antiperiplanar positions predominates with a fractional population in the range 0.6–1. In the series of compounds investigated ³J_HF increase and ²J_HF decrease with increasing electronegativity of substituents, thus showing an unusual trend. For these couplings a modest but significant solvent dependence has been also observed. The INDOR technique has proved to be a useful tool for the separation of overlapping spectra of diastereoisomeric pairs.