High-level ab initio calculations demonstrate that alkoxy-thiocarbonyl radicals (ROC*=S) undergo beta-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.
ARC Centre of Excellence in Free Radical Chemistry and Biotechnology, Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia. mcoote@rsc.anu.edu.au
