Interpretation of the reactivity of benzyl free radical towards peroxyacids in terms of orbital interactions. Competition between energy gap control and overlap control

Abstract

The factors which control the reactivity of alkyl free radicals R˙ in reaction (i) are studied. The reactivity [graphic omitted] R′→ R – OH + R′CO˙₂(i), of R˙ in (i) depends on the key orbital interaction between the SOMO of the radical and the LUMO of the peroxyacid. This interaction involves two contributions: (i) the energy gap SOMO–LUMO and (ii) the overlap SOMO–LUMO. In reaction (i) the main factor is overlap control which depends on spin delocalisation in the radical R˙. This proves that reaction (i) does not involve electron transfer. The energy gap control, which depends on the nucleophilic character of R˙, is only observed when the first factor is constant along a series of R˙.