| Abstract | Rate constants for the free-radical rearrangement, RC(O)OCMe2CH2 → RC(O)OCH2CMe2, and for the ring-opening reaction, RĊOCH2CMe2O → RC(O)OCH2ĊMe2, have been measured by kinetic EPR spectroscopy. In hydrocarbon solvents at 75°C with R = methyl and phenyl, the 1,2-acyloxy migrations are slower (k = 5.1 × 102 s-1 and 2.5 × 102 s-1, respectively) than the corresponding 1,3-dioxolan-2-yl ring openings (k = 7.6 × 103 s-1 and 1.0 × 103 s-1, respectively). The formation of a 1,3-dioxolan-2-yl radical as an intermediate in these two rearrangements could not, therefore, be ruled out. However, with R = cyclopropyl, the rearrangement proceeded normally (k ≈ 1.2 × 102 s-1 at 75°C), but the corresponding 1,3-dioxolan-2-yl radical underwent opening of the cyclopropyl ring rather than the dioxolanyl ring. Since this process occurred at a much faster rate (k = 8.7 × 105 s-1 at 75°C) than the rearrangement, the dioxolanyl radical cannot, in this case at least, be an intermediate in this acyloxy migration. The possible role of charge separation in the transition state for acyloxy migration is considered. © 1982 American Chemical Society. |
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