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-d6) as dilute solutes have been studied in a wide variety of organic solvents. The results obtained show that intermolecular interactions affect vibrations of all the groups in the molecules of the solute, but in different ways and to different extents. The dipole related SO stretching mode in both DMSO and DMSO-d6 appears to be the most sensitive to the molecular environment. Bands corresponding to the νa(CSC) A'' asymmetric stretch in DMSO and the r∥(CD3) A' rocking vibration in DMSO-d6 were also chosen as probe modes because they are more clearly observed in all the studied solutions. Complications in the spectrum of DMSO due to the strong overlaps of the bands were avoided by using DMSO-d6. The relative contributions of specific and nonspecific solvation effects were evaluated using a linear solvation energy relationship (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 effect on the equilibrium of two resonance forms of DMSO in solution.