Theoretical model for the reaction mechanisms of singlet carbene analogs into unsaturated hydrocarbon and the origin of the activation barrier

Abstract

The addition of singlet carbene analogs XR2 (X=C, Si, Ge, and Sn; R=H and F) into ethylene have been investigated by ab initio molecular orbital methods. The reaction mechanisms are two-step processes. The first step is the complex formation, the CX bond formation of one site, with the interaction between the empty pπ orbital of carbene analogs and the π orbital of ethylene, and the second is the other CX bond formation with biradical coupling (addition). The transition states correspond to the intermediate process between the first and the second steps. The localized molecular orbital (LMO) configuration analysis along the intrinsic reaction coordinate (IRC) path showed important singlet excitation character for the transition state. An increase in the energy barrier heights for the above systems is associated with a general increase in the singlet excitation energies of carbene analogs XR2. On the basis of the proposed reaction mechanism, the heats of formation for the treated reaction systems were estimated. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 291–302, 1998