The beta-(Phosphatoxy)alkyl radical rearrangement. Rate constants, Arrhenius parameters, and structure activity relationships

Rate constants for the migration of a series of p,p-disubstituted beta-(diarylphosphatoxy)alkyl migrations have been determined in benzene at reflux by competition against the benzeneselenol clock reaction. There is a strong linear correlation of log(k) with the Hammett sigma(p) but not with various sigma(.) parameters indicating that the migration occurs through a highly polarized transition state resembling an alkene radical cation loosely bound to a phosphate anion, The Arrhenius equation describing the migration of the beta-phenyl-beta-(diphenylphosphatoxy)ethyl radical in toluene was found to be. log(k(R)) = (10.2 +/- 0.8)- (7.0 +/- 1.0)/2.3RT.