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作 者:HUANG Ze-En LIANG Xiao-Guang LEUNG Hiu-Kwong CHAN Yuk-Yee
机构地区:[1]Institute of Photographic Chemistry,The Chinese Academy of Sciences,Beijing 100101
出 处:《Chinese Journal of Chemistry》1991年第6期506-511,共0页中国化学(英文版)
基 金:This report was partially supported by the National Natural Science Foundation of China
摘 要: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 evidence 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 the reaction and electron-donating substituent increasing the reaction rate. However, steric bulkiness at the 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 evidence 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 the reaction and electron-donating substituent increasing the reaction rate. However, steric bulkiness at the 6-position does not play an important role in the reaction rate.
关 键 词:rate Kinetic studies on the singlet oxygenation of 6-ethyl-3 4-dihydro-2H-pyran-5-carboxylic acid ethyl ester and 6-isopropyl-3 4-dihydro-2H-pyran-5-carboxylic acid ethyl ester Sensitized photooxygenation acid VI
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