A dynamic 1H nuclear magnetic resonance spectral study of 1,4-dithian and of its dihalogen complexes

Abstract

The cyclic ligand 1,4-dithian, C₄H₈S₂, readily forms complexes with halogens and the ¹H n.m.r. spectra of these complexes and of 1,4-dithian itself have been studied over a wide temperature range. At low temperatures a coalescence phenomenon was observed in the spectrum of 1,4-dithian which has been attributed to the onset of rapid ring reversal occurring in the molecule. The AA'BB' spectrum observed below coalescence has been analysed and it proved possible to simulate the appearance of the spectrum over a temperature range by using n.m.r. band shape fitting techniques. A coalescence phenomenon was also observed in the spectra of the complexes C₄H₈S₂,2Cl₂ and C₄H₈S₂,2Br₂. This coalescence was found to be due not to reversal of the 1,4-dithian ring, but rather to inversion of configuration at the sulphur atoms. Thermodynamic activation parameters are reported for both ring reversal of 1,4-dithian and for inversion of configuration at the ligand atoms in the halogen complexes.