Transition structure for hydride transfer from cyclopropene to azirinium cation

Abstract

The transition structure for the hydride transfer between the cyclopropene and azirinium cation has been characterized by means of the ab initio method at the 3-21G, 4-31G, 6-31G, 6-31 + + G ∗ basis set levels. There are two transition structures for the exo and endo conformations. The transferring hydrogen is located closer to the acceptor centre, nitrogen atom, than to the donor centre, carbon atom, with an almost bent arrangement. The electronic structure and transition vector are basis set level independent. For the transition structures, the endo is more stable than the exo conformation due to a favourable orbital interaction. An analysis of calculated transition structure associated with the hydride transfer step in different model systems shows that the use of very simple models to represent this step do not alter their nature. The transition structures for hydride transfer step seems to be a robust entity. Furthermore, there is a minimal molecular model with a transition structure and transition vector which describes the essentials of the chemical interconversion step.