Factors affecting the relative and absolute rates of β-scission of alkoxythiocarbonyl radicals and alkoxycarbonyl radicals

High-level ab initio calculations demonstrate that alkoxythiocarbonyl radicals (ROC^.=S) undergo β-scission significantly faster than alkoxycarbonyl radicals (ROC^.=O) despite having similar exothermicities. The relatively low reactivity of the ROC^.=O radicals is reduced further by electron-donating R groups and arises from the large polarization of the C^.-O bonds of the reactant radicals. The results suggest that the generation of alkyl radicals from ROC^.=S should be particularly efficient when the R group bears radical-stabilizing and/or electron-accepting groups, such as CN.