Theoretical reinvestigation of opposite electronic effects on bond lengths in thiophenols and thiophenolic radicals

Our previous study has revealed that para-substituents have opposite electronic effects on the C-S bond lengths of thiophenols and thiophenolic radicals. Although a theoretical elucidation has been given, it has not been supported by theoretically calculated atomic charges. To give an alternative explanation, we calculated the C-S bond lengths, C-S bond electron densities, and Mulliken charges on the carbon and sulfur atoms for thiophenols, thiophenolic radicals, and thiophenolic radical cations by means of the B3LYP density functional theory method using the 6-31G(d, p) basis set. It was revealed that the C-S bond length is adequately defined in terms of C-S bond electron density. The distinct electronic effects on the C-S bond lengths of thiophenols, thiophenolic radicals and thiophenolic radical cations are well elucidated by the different electronic states (electron-deficient or-rich) of the phenyl ring and SH group.