The mechanisms of the abstraction reactions of alkylidenecarbenes have been characterized in detail using density functional theory. All the stationary points were determined at the B3LYP/6-311G(d, p) level of the theory. The transition states both to the reactants and the product direction in the reaction paths were examined by using the intrinsic reaction coordinate. A configuration mixing model based on the work of Pross and Shaik was used to rationalize the computational results. The results show that the electro negativity of the substituents played an important role in predicting its activity for the abstraction reactions. The major conclusion was that the stronger the π-donation or the more electro negativity the substituents, the smaller the ΔE_ST of XYC＝C and the lower the activation energy for the abstraction reactions. In other words, it is the electronic factors, rather than the steric factors, that play a decisive role in the chemistry of the alkylidenecarbene species. Furthermore, a comparison with oxirane also led to the same result.

Key words: alkylidenecarbene, ab initio, density functional theory, transition state