Sulfur–chlorine bond dissociation enthalpies in methane- and benzene-sulfonyl chlorides

Sulfur-chlorine bond dissociation enthalpies in methane- and benzene-sulfonyl chlorides, D(RSO2–Cl), were measured by photoacoustic calorimetry and were found to be equal within experimental error (295 kJ mol–1). The implicit absence of a stabilizing effect of the phenyl group in PhSO2˙ is consistent with the known spectroscopic properties of sulfonyl radicals but conflicts with the currently accepted thermochemical data. Appearance energy measurements lead to values for the radical ionization potentials, Ei(MeSO2)= 8.67 and Ei(PhSO2˙)= 7.49 eV and for the enthalpy changes associated with the heterolytic cleavages RSO2Cl→RSO2++ Cl– where a substituent effect is observed.