Time-Resolved Mechanism of the Cycloaddition Reaction between Difluorocarbene and Norbornadiene

Cycloaddition between difluorocarbene and norbornadiene is a stepwise process where a non-linear cheletropic transition state (TS1) leads to a diradical intermediate, followed by 1,2- and 1,4-addition. Quasi-classical molecular dynamic simulation correctly predicts the selectivity of 1,4-addition product over the 1,2-addition one, however, transition state theory failed. Dynamic effect is observed during simulation, in which the velocity of vibrational mode 2 of TS1 influences the destination of trajectories, the velocity of vibrational mode 4/6 influences the time spent by trajectories to reach 1,4- and 1,2-addition product. The fast trajectories constitute ballistic mechanism.