S—H Bond Dissociation Enthalpies in para- and meta-Substituted Thiophenols: Correlation with Thiophenolic C—S Bond Length

For mono-substituted anilines, phenols, and thiophenols it has been found that N—H, O—H and S—H bond dissociation enthalpies (BDE) depend on Hammett constants approximately linearly. For substituents placed in meta position, linearity of found dependences is usually considerably worse in comparison to para-substituted molecules. Therefore, their applicability for prediction of changes in BDE using substituent Hammett constant may be limited. In this work, we have found that the length of thiophenolic C—S bond, R(C—S), or its shortening after hydrogen atom abstraction, ΔR(C—S), represent suitable descriptors of substituent induced changes in S—H BDE. For fifteen studied meta-substituted thiophenols, these geometry descriptors correlate with S—H BDEs considerably better than Hammett constants.