An ab initio and DFT study of homolytic substitution reactions by oxyacyl radicals at sulfur, selenium, and tellurium

Homolytic substitution reactions of methoxycarbonyl radicals at the sulfur, selenium, and tellurium atoms in dimethyl sulfide, dimethyl selenide, and dimethyl telluride have been investigated using computational techniques. Ab initio and DFT calculations predict that attack of methoxycarbonyl radical at the sulfur and selenium containing molecules proceed via smooth transition states without the involvement of hypervalent intermediates. BHandHLYP/DZP calculated energy barriers (ΔE‡) for these reactions range from 58.3 (S) to 34.6 (Se) kJ mol−1. In contrast, calculations on the analogous reaction involving tellurium predict the involvement of an intermediate at MP2/DZP. BHandHLYP/DZP calculations provide an energy barrier (ΔE‡) of 7.7 kJ mol−1 for the reaction involving tellurium. These homolytic substitution reactions are predicted to be exothermic at all levels of theory with the forward reactions favoured by 11–28 kJ mol−1 for attack at sulfur, 4–23 kJ mol−1 for attack at selenium and by only 1–3 kJ mol−1 for attack at tellurium.