A comparison of orbital interactions in the additions of phosphonyl and acyl radicals to double bonds.
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 pi*(C=O)<--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 sigma*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.
Krenske
Elizabeth H
EH
Australian Research Council Centre of Excellence for Free Radical Chemistry and Biotechnology, Australia. krenske@chem.ucla.edu
Schiesser
Carl H
CH
D000475:Alkenes / Q000737:chemistry*; D003198:Computer Simulation; D005609:Free Radicals / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure; D063065:Organophosphonates / Q000737:chemistry*; D011789:Quantum Theory; D013816:Thermodynamics
D000475:Alkenes; D005609:Free Radicals; D063065:Organophosphonates