Oxygen radicals, -cleavage rearrangement

Kharasch has pointed out that there are two very similar and not easily distinguished reactions of oxygen radicals, /9-cleavage and rearrangement.111 The difficulty is that they can often lead to the same final product. 

The decomposition of t.ert-bvA.y triarylmethyl peroxides is particularly well suited to the measurement of migration aptitudes in oxygen radicals because the nature of the product leaves no doubt that the reaction is in fact a rearrangement rather than a /9-cleavage. 

Examples of intramolecular trapping of carbonyl ylide dipoles by alkenes have now been reported.These include, for example, the conversion of the oxirane (172) into the tetrahydrofuran (173). Carbonyl ylides have also been prepared by irradiation of 2,3-bis-(p-methoxyphenyl)oxirane in the presence of dicyanoanthracene as electron-transfer sensitizer direct or triplet-sensitized irradiation, however, leads mainly to rearrangement via carbon-oxygen bond cleavage. In contrast, cyclohexene oxide and styrene oxide, on naphthalene-sensitized irradiation in alcohols, undergo solvolysis via oxide anion-radical intermediates. ... 

Leffler, J. E. Cleavages and rearrangements involving oxygen radicals and cations. Chem. Rev. 1949,45, 385-417. 

The m/z 57 ion, which does not contain a chlorine atom, since the ion at m/z 59 is almost absent, is derived from the cleavage of the bond adjacent to the sp3 oxygen. The fragment at m/z 56 is an even-mass one in the absence of nitrogen, this means that a radical cation is formed by a rearrangement ... 

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