Substituent effects on the formation of sulfonyl cations from sulfonyl chlorides: comparisons of solvolysis kinetic data with calculated gas phase energies

Abstract

AbstractSuitable theoretical methods are validated for organosulfur compounds using experimental data for gas phase enthalpies of formation, proton affinities (PA) and heterolytic bond dissociation enthalpies (HBDEs). From enthalpies of chloride anion transfers from neutral chlorides to acyl, sulfonyl or cumyl cations in the gas phase, it is calculated that (i) similar aromatic substituent effects are expected for heterolyses of acyl, sulfonyl and cumyl chlorides; (ii) HBDEs for loss of chloride increase by over 70 kcal mol−1 from 4‐MeOC6H4COCl to SO2Cl2. Rate constants for solvolyses of 4‐Z‐substituted arenesulfonyl chlorides (Z = OMe, Me, H, Cl, NO2) in 97% w/w 2,2,2‐trifluoroethanol (TFE)–water are reported. Substituent effects are smaller than observed for identical solvolyses of acyl and cumyl chlorides, and are much smaller than those predicted theoretically for gas phase unimolecular heterolysis (explained by variable amounts of nucleophilic solvent assistance). Copyright © 2007 John Wiley & Sons, Ltd.