Oxygen radicals orbital overlap

The yield of alcohol ROH depends on the nucleophility of the radical as well as on the degree of the delocalization of an unpaired dectron. If the unpaired electron is not ddocalized, the reactivity of the n-alkyl radical increases with its nucleophility which may be correlated with the ionization potential. On the other hand, if the unpaired spin is delocalized, the orbital overlap of the radical and the peroxidic oxygen becomes an important reactivity factor. A radical seemingly... 

Similarly, the antioxidant activity of vitamin E is centreed on its chainbreaking donor activity in-vitro rate studies on a-tocopherol have shown that it is one of the most efficient alkylperoxyl radical traps, far better than commercial hindered phenols such as BHT, 2,6-di- ferf.butyl-4-methylphe-nol. Its efficiency was attributed [30, 31] to the highly stabilised structure of tocopheroxyl radical (which is formed during the rate-limiting step, reaction 3) because of favourable overlap between the p-orbitals on the two oxygen atoms. 

Additional evidence comes from the study of the radical cations of trans- and cis-methyl-2-phenycyclopentyl ether and trans- and di -l-methyl-2-phenylcyclopentane, where only the first radical cation undergoes C-C bond cleavage since in this case in addition to the overlap between the scissible bond and the Tt-system, the conformation of the methoxy group allows interaction of a nonbonding electron pair on the oxygen with the a orbital of this bond [183, 184]. 

Since in these systems intramolecular electron transfer involves orbitals which cannot directly overlap, a point which has attracted great interest is whether or not the radical zwitterion and the oxygen centered radical are different representations of a single species. In addition, the mechanistic picture can be further complicated since intramolecular electron transfer in the radical zwitterion can be coupled with or followed by other processes (i.e. C -C/j bond cleavage or 1,2-carbon to oxygen H atom shift with I, and decarboxylation with II and IE). Finally, it is also interesting to understand if in systems such as II and III, decarboxylation requires or not initial O-H deprotonation. 

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