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Mechanism of Abstraction Reactions of Heavy Cyclopropenes with Carbon Tetrachloride

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journal contribution
posted on 02.08.2007 by Chi-Hui Chen, Ming-Der Su
The potential energy surfaces for the abstraction reactions of heavy cyclopropenes (X−Y−Z) with carbon tetrachloride have been characterized in detail using density functional theory (B3LYP), including zero-point corrections. Five cyclopropene analogues including A(CCC), B(GeSiSi), C(SiSiSi), D(SiSiGe), and E(GeGeGe), have been chosen in this work as model reactants. Two reaction paths, the Cl abstraction I and the CCl3 abstraction II, have been considered in the present study. Our theoretical findings strongly suggest that the former is more favorable, with a very low activation energy and a large exothermicity. This is in accordance with available experimental observations. Moreover, our theoretical investigations also indicate that the more electropositive the elements making up the double bond of a heavy cyclopropene, the lower its activation barrier and the more exothermic the haloalkane abstraction. That is, electronic factors play a dominant role in determining the chemical reactivity of the heavy cyclopropene species kinetically as well as thermodynamically. Furthermore, a configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results. The results obtained allow a number of predictions to be made.