NMR parameters of sulphur heterocycles: Solvent and concentration effects for thiophen and related systems

Infinite dilution data for six sulphur heterocycles have been obtained from second order analyses of their NMR spectra in CS₂, CDCl₃, CD₃COCD₃, or C₆D₆. Use of LAOCOON3 leads to accurate chemical shifts, but substantial errors remain in some of the coupling constants. Evidence is presented of specific association of chloroform with the sulphur heterocycles and of the interaction of acetone with the sulphur atom. An apparently anomalous geometry for the complex of benzene with thiophen and with other solutes is discussed. Dilution effects are considered in relation to the formation of solute dimers.