3d-Orbital participation and ultraviolet spectra of thiophenols

Absorption intensities of the lower-frequency u.v. transition in phenol, thiophenol, p-methylphenol, and p-methylthiophenol have been measured at room temperature and at 77°K. Integrated intensities at 77°K were obtained. The change in absorption intensity of the 1Lbâ†�1A band (Aâ†�X) when going from thiophenol to p-methylthiophenol does not support the hypothesis of 3d-orbital participation to π-bonding between sulphur and the aromatic ring put forward by Goodman and Taft. An increase in intensity is observed which is consistent with 3pπ(S)–2pπ(C) bonding.