S-H bond dissociation enthalpies in thiophenols: A time-resolved photoacoustic calorimetry and quantum chemistry study

Time-resolved photoacoustic calorimetry (TR-PAC) and quantum chemistry calculations were used to investigate the energetics of sulfur-hydrogen bonds in thiophenol and four para-substituted thiophenols, 4-XC6H4SH (X = CH3, OCH3, Cl, and CF3). The result obtained for the PhS-H gas-phase bond dissociation enthalpy, derived from the PAC experimental results in solution, is 349.4 +/- 4.5 kJ mol(-1). This value is significantly higher than recent literature values but agrees with a value suggested some 20 years ago in a widely used review. The PAC result also concurs with the value computed at a high theory level, G3(MP2), 346.8 kJ mol(-1). The data obtained for the substituted thiophenols support the idea that substituent effects are less pronounced on the S-H bond dissociation enthalpy than on the O-H bond dissociation enthalpy of the corresponding phenols.