Mechanism of rearrangement of \u3b2-(acyloxy)alkyl radicals

Rate constants for the free radical rearrangement, CF 3C(O)OCMe 2\u10aH 2 (1d) \u2192 CF 3C(O)OCH 2\u10aMe 2 (2d), have been measured in CF 2ClCFCl 2 by kinetic EPR spectroscopy. This reaction is very significantly faster (k 1 75\ub0C = 7.0 7 10 4 s -1) than the related rearrangement, CH 3C(O)OCMe 2\u10aH 2 (1a) \u2192 CH 3C(O)OCH 2\u10aMe 2 (2a) (k 1 75\ub0C = 4.5 7 10 2 s -1), in hydrocarbon solvents. The potential cyclic intermediate radical, 2-(trifluoromethyl)-4,4-dimethyl-1,3-dioxolan-2-yl (3d), does not undergo ring opening to 2d, at temperatures where the 1d \u2192 2d rearangement is very fast. It is concluded that 3d is not an intermediate in the trifluoroacetoxyl migration. It is also concluded on the basis of the k 1 values for 1a and 1d that these rearrangements involved a charge-separated transition state. The 1a \u2192 2a rearrangement is very much faster in water (k 1 75\ub0C = 2.1 7 10 4 s -1) than in hydrocarbon solvents, which provides additional support for a charge-separated transition state.Peer reviewed: YesNRC publication: Ye