Mass spectrometric and theoretical studies on dissociation of the CS bond in the benzenesulfonic acid and benzenesulfinic acid anion series: Homolytic cleavage vs heterolytic cleavage

The dissociation of the CS bond in a variety of para-substituted benzenesulfonic acid and benzenesulfinic acid anions has been investigated through the tandem mass spectrometry and density functional theory (DFT). For the CS bond in the para-substituted benzenesulfonic acid anions, only the homolytic cleavage occurs. DFT calculations indicate that the homolytic cleavage is 14.1 kcal/mol at least less than the heterolytic cleavage in the dissociation enthalpy. On the other hand, for the CS bond in the para-substituted benzenesulfinic acid anions, both homolytic cleavage and heterolytic cleavage take place. Calculations show that the enthalpy difference between these two cleavage modes is 9.5 kcal/mol at most. It is obvious that DFT calculations are well consistent with the MS/MS experiments.