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Kinetic studies of the singlet oxygenation of the title compounds were performed accord-ing to Monroe’s method. The reaction rate increases with temperature decreasing, leading to a ne-gative activation enthalpy and a large negative activation entropy. These data are interpreted as theevidence for the intermediacy of an exciplex. The solvent effect on the reaction rate suggests that the“dioxetane” path involves a transition state or an intermediate with significant zwitterionic character.The electronic effect of the substituent is obvious, with electron-withdrawing substituent retarding thereaction and electron-donating substituent increasing the reaction rate. However, steric bulkiness atthe 6-position does not play an important role in the reaction rate.
Kinetic studies of the singlet oxygenation of the title compounds were performed accord-ing to Monroe’s method. The reaction rate increases with temperature decreasing, leading to a ne-gative activation enthalpy and a large negative activation entropy. These data are interpreted as the virgin for the intermediacy of an exciplex. The solvent effect on the reaction rate suggests that the “dioxetane” path involves a transition state or an intermediate with significant zwitterionic character. The electronic effect of the substituent is obvious, with electron-withdrawing compound retarding thereaction and electron- donating substituent increasing the reaction rate. However, steric bulkiness atthe 6-position does not play an important role in the reaction rate.