Nuclear magnetic resonance measurement of the small barrier to rotation about the carbon–carbon bond in 3,5-dichlorobenzyl mercaptan

Abstract

The analysis of the proton magnetic resonance spectrum of a 10 mol % solution of 3,5-dichlorobenzyl mercaptan in deuterated benzene yields –0.42 Hz for the spin–spin coupling constant over six bonds between the methylene protons and the ring proton in the para position. A hindered rotor treatment, combined with the assumption of a simple angle dependence of the spin–spin coupling, yields a value of 1.8 ± 0.2 kcal mol^–1 for the twofold barrier to rotation about the carbon–carbon bond. The low-energy conformation is that in which the carbon–sulphur bond lies in a plane perpendicular to that of the benzene plane.