An ab initio study of the mechanism of the cycloaddition reaction forming bicyclic compounds between vinylidene (H2C=C:) and ethylene

The mechanism of the cycloaddition reaction forming a bicyclic compounds between singlet vinylidene (H2C=C:) and ethylene was investigated using the CCSD(T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that this reaction has one dominant channel. The presented rule of this reaction, a [2+2] cycloaddition reaction between the two reactants occurred forming a four-membered ring carbene (INT1), in which the sp lone electron of the C atom from carbene in INT1 and the pi* unoccupied orbital of ethane form the sp ->pi* donor acceptor effect, resulting in the formation of intermediate (INT2). Due to the further sp(3) hybridization of C atom from carbene in INT1, INT2 isomerizes to the bicyclic compound (P2) via the transition state (TS2).