Sensitized photooxygenation VI. 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

Autor:	Xiao-Guang Liang, Yuk-Yee Chan, Ze-En Huang, Hiu-Kwong Leung
Rok vydání:	2010
Předmět:	chemistry.chemical_classification Carboxylic acid Substituent General Chemistry Medicinal chemistry Dioxetane Reaction rate chemistry.chemical_compound chemistry Pyran Organic chemistry Photooxygenation Solvent effects Isopropyl
Zdroj:	Chinese Journal of Chemistry. 9:506-511
ISSN:	1001-604X
DOI:	10.1002/cjoc.19910090605
Popis:	Kinetic studies of the singlet oxygenation of the title compounds were performed according to Monroe's method. The reaction rate increases with temperature decreasing, leading to a negative 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.
Databáze:	OpenAIRE
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