Spin adducts of group IVB organometallic radicals with Thioketones. an esr study

The radical adducts resulting from the reaction between Groiup IVB organometallic radicals .MR3 (M = Si, Ge, Sn; R = alkyl or aryl) and a number of thioketones of the chromone and flavone series have been investigated by ESR spectroscopy. The spectral parameters obtained for these species have been compared with those of similar adducts of the corresponding ketones. Both classes of radicals adopt an orthogonal conformation, and differences between the former and the latter paramagnetic species can be accounted for by the different electronegativity of oxygen and sulphur. The effects of substitution of the heterocyclic oxygen with a sulphur or a seleniun atom on the spin density distribution are likewise explained. INDO calculations have been carried out on the model system .CH2XSiH3 (X = O, S).