DIRECT MEASUREMENTS OF THE RATES OF 1,3-SIGMATROPIC AND 1,5-SIGMATROPIC HYDROGEN SHIFTS IN THE PHOTO-FRIES REARRANGEMENTS OF PHENYL ACETATE

The rate constants for the 1,3- and 1,5-sigmatropic hydrogen shifts of the photo-Fries rearranged intermediates of phenyl acetate produced b y laser flash photolysis at 266 nm were directly measured in several s olvents. The rate constant for the 1,3-hydrogen shift (3.6 s-1) was fa ster than that for the 1,5-shift (6.5 x 10(-2) s-1) in the ground stat e in methylcyclohexane at 293 K, contrary to the expectation by the Wo odward-Hoffmann rule. In protic solvents, ethanol and methanol, a rema rkable increase in the rate constants (approximately 10(5) s-1) was ob served. A tentative mechanism including the role of the non-bonding el ectrons of the intermediates is discussed.