ORIGINS OF THE ACIDITY TRENDS IN DIMETHYL SULFIDE, DIMETHYL-SULFOXIDE, AND DIMETHYL SULFONE

We present a theoretical study into the origin of the acidity trends i n the series dimethyl sulfide (Dh?MS), dimethyl sulfoxide (DMSO), and dimethylsulfone (DMSO(2)). Calculations at the HF/6-31++G*//HF/6-31+G* level of theory reproduce the observed acidity trend, DMSO(2) > DM SO > DMS. The relative acidity is found to be an inherent property of the acid and the relative stability and geometric relaxation within th e anion are unimportant. Detailed investigation of the energetics at t he atomic level reveals that the origin of the relative acidities with in the series is a greater destabilization of the CH3SCH2 fragment in the acid with increasing oxygen substitution than in the associated an ion. We find no evidence in the atomic properties and the topological properties of the charge density for an appreciable delocalization of charge from the anionic carbon in the anion.