Proton spin–lattice relaxation study of intermolecular interactions in the methanol + dimethylsulphoxide liquid system

Abstract

The intra- and inter-molecular contributions to the proton spin-lattice relaxation rate [(1/T₁)^expt] for the methyl and hydroxyl groups of methanol as well as for dimethylsulphoxide (DMSO) in the methanol + DMSO liquid system were determined as a function of composition at temperatures between 0 and 41.4°C. The distances of closest approach between two groups [d(R–R′)] for various intermolecular interactions were evaluated from the intermolecular contributions to (1/T₁)^expt. A comparison of the d(R–R′) values reveals that the order of magnitude in the intermolecular interactions in the equimolar and methanol-rich mixtures is: OH–OH > OH–DMSO > Me–DMSO ∼ Me–Me. In the methanol-poor mixtures the order changes to: OH–DMSO ≳ OH–OH > Me–DMSO > Me–Me. There seems to be a distinct change in liquid structure going from the methanol-rich to -poor mixtures.