Mechanism of abstraction reactions of heavy cyclopropenes with carbon tetrachloride.

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(C-C-C), B(Ge-Si-Si), C(Si-Si-Si), D(Si-Si-Ge), and E(Ge-Ge-Ge), 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.