SOLVENT-INDUCED FREQUENCY-SHIFTS IN THE INFRARED-SPECTRUM OF DIMETHYL-SULFOXIDE IN ORGANIC-SOLVENTS

Solvent-induced frequency shifts in the infrared spectrum of dimethyl sulfoxide (DMSO) and deuterated dimethyl sulfoxide (DMSO-d(6)) as dilu te: solutes have been studied in a wide variety of organic solvents. T he results obtained show that intermolecular interactions affect vibra tions of all the groups in the molecules of the solute, but in differe nt ways and to different extents. The dipole related S=O stretching mo de in both DMSO and DMSO-d(6) appears to be the most sensitive to the molecular environment. Bands corresponding to the nu(a)(CSC) A '' asym metric stretch in DMSO and the r(parallel to)(CD3) A' rocking vibratio n in DMSO-d(6) were also chosen as probe modes because they are more c learly observed in all the studied solutions. Complications in the spe ctrum of DMSO due to the strong overlaps of the bands were avoided by using DMSO-d(6). The relative contributions of specific and nonspecifi c solvation effects were evaluated using a linear solvation energy rel ationship (LSER). Simple linear equations were obtained for evaluation (prediction) of the solvent induced frequency shifts in the infrared spectrum of DMSO. The results are explained in terms of the solvent ef fect on the equilibrium of two resonance forms of DMSO in solution.