The decarboxylation of �-ketoacids and closely related reactions are common in both biological reactions and synthetic organic sequences, and their mechanisms have been studied extensively by other experimental and computational methods. Our approach has been to experimentally characterize the decarboxylation of benzoylacetic acid by its 13C kinetic isotope effects determined at natural abundance by NMR methodology, then carefully examine the reaction computationally in order to understand the combination of computational method and theoretical model that accounts for the experiments. In doing so, we have found that the experimental KIE of the methyl carbon in acetophenone which is formed from the decarboxylation of benzoylacetic acid is 1.041 � .001. Using method and basis set M062X/6-31+G**, we have found that these experimental observations match very simplistic computational models. However, after further study of the reaction by POLYRATE and dynamic trajectory studies, it is found that the theoretical KIE should be 1.044.  The results define a reaction on the border of general and specific acid-base catalysis, and illustrate the common origin of the catalysis at this borderline based on the dynamics of the proton-transfer and heavy-atom motions in the reaction that provides a clearer insight into the nature of the catalysis.

Isotope effects and dynamics in the decarboxylation of b-ketoacids: Lifetime and the nature of acid catalysis

247th National Meeting (2014)

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