Group IVB heterocyclic compounds. Oxidation rates, carbon-13 nuclear magnetic resonance, and photoelectron spectra of 10,10-dimethylphenothia-silin, -germin, and -stannin derivatives and of 9,9-dimethylthioxanthen
10,10-Dimethylphenothia-silin and -germin have been prepared for the first time and their properties compared with those of the corresponding tin derivative and of 9,9-dimethyithioxanthen. The 13C n.m.r. spectra of these compounds suggest increasing strain in the heterocyclic framework on going down Group IVB. The oxidation rates of sulphur to sulphinyl group with perbenzoic acid have been measured in carbon tetrachloride. The first few bands in the photoelectron (HeI) spectra are assigned by comparison with the spectra of related compounds. The reactivity sequence and the ionization energy data indicate that, for geometrical changes along the series, the interaction between the sulphur lone pair and the benzene rings decreases on going towards the Sn derivative.