Abstract
Bond strength in the lowest excited singlet state and enthalpy changes in reaction estimated by semiempirical AM1 calculations showed that β cleavage proceeds more favorably than α cleavage at the carbamoyl moiety of O-aryl N-methylcarbamates. The spin density at each atom of a phenoxy radical derivative formed via β cleavage indicated that radical reactivity are higher at the oxygen atom and the o- and p-positions of the phenyl ring. In subsequent photo-Fries rearrangement, cyclohexadienone intermediates were theoretically suggested. Regioselectivity in the rearrangement was well elucidated by enthalpy changes along the proposed photodegradation pathways and the spin density of the phenoxy radicals.
