A comparison of orbital interactions in the additions of phosphonyl and acyl radicals to double bonds

Abstract

Calculation of the barriers for addition of the H₂P(O)˙ and HC(O)˙ radicals to alkenes, at the CCSD(T)/aug-cc-pVDZ//BHandHLYP/6-311G** level, indicates that both radicals display ambiphilic behaviour. For the HC(O)˙ radical this behaviour occurs because a secondary orbital interaction of the type π*_CO←HOMO acts in conjunction with the primary SOMO←HOMO interaction to balance the SOMO→LUMO interaction. For the H₂P(O)˙ radical, on the other hand, the much higher-lying LUMO (the σ*_P–O orbital) allows for only minimal secondary interaction, and this radical's ambiphilic behaviour is therefore reflective of a balance between SOMO→LUMO and SOMO←HOMO interactions.