THE NEOPHYL-LIKE REARRANGEMENT OF ALKOXYL RADICALS REVISITED - LASER FLASH AND LASER DROP PHOTOLYSIS STUDIES OF 1,1-DIPHENYLETHOXYL RADICALS

The radical 1,1-diphenylethoxyl (III) has been generated by laser photodecomposition of tert-butyl 1,1-diphenylethyl peroxide (II). Radical III shows a visible absorption with lambda(max) 535 nm and decays by phenyl migration to yield the 1-phenoxy-1-phenylethyl radical (V). The conversion III --> V occurs with an activation energy of 5.9 +/- 0.4 kcal/mol and a preexponential factor (log A/s(-1)) = 10.77 +/- 0.35, corresponding to a lifetime for III of similar to 400 ns in acetonitrile at room temperature. In the nanosecond time scale, the formation of V occurs concurrently with the decay of III. The results suggest that there is no need to invoke the intermediacy of the neophyl-like bridged intermediate IV. This intermediate is probably involved but if so is short-lived and not detectable with nanosecond laser photolysis techniques. The conclusion of earlier reports involving the characterization of IV needs to be revised. High-intensity laser excitation of II under laser drop conditions shows that III undergoes C-C photocleavage to yield acetophenone and benzophenone with virtually no selectivity.