Dynamics of the biradical mediating vinylcyclopropane-cyclopentene rearrangement

A previous direct dynamics trajectory study of the thermal vinylcyclopropane cyclopentene rearrangement [C. Doubleday, J. Phys. Chem. A, 2001, 105, 6333], based on an AM1-SRP potential energy surface (PES), is extended to study details of the intramolecular and unimolecular dynamics in the biradical region of the PES. The branching ratio of the 4 diastereomeric products and the time dependence of their formation depend on the transition state at which the trajectories are initialized and its vibrational temperature or mode specific excitation. For the small amount of reaction occurring after similar to600 fs, there is considerable stereorandomness in the product yield, which contrasts with the short-time nonstatistical and mode specific reaction. Varying the initial amount of energy in reaction coordinate translation has only a minor effect on the biradical lifetime, but may have an appreciable effect on the relative product yield. Changing the rotational temperature has a negligible effect on the reaction dynamics. This study illustrates the utility of the quasiclassical trajectory method for studying short-time unimolecular dynamics and the importance of including zero-point energy motion in the trajectory initial conditions.