Spectroscopic study of the solvation of dimethyl sulfoxide in aqueous acetonitrile and acetone solvent systems

Results of IR studies of dimethyl sulfoxide (DMSO) in water and aqueous acetonitrile and aqueous acetone mixtures are reported. These data, along with those reported previously for a series of amides in mixed solvents, yield information about the composition of the first solvation shell of the S=O or C=O chromophore in the mixed solvent. It is shown that, for each of the systems considered, the composition of the chromophore's first solvation shell can be reproduced quantitatively by a simple mass action treatment, using only one adjustable parameter. This is the mean equilibrium constant, K*, for the replacement of one component of the mixed solvent by the other in the coordination shelf of the chromophore. It is also shown that DMSO, Like amides, can form two hydrogen bonds at the S=O oxygen.