Photochemical isomerization reactions of acrylonitrile. A mechanistic study

The mechanisms for the photochemical isomerization reactions are determined theoretically using the acrylonitrile model molecule. The CASSCF (twelve-electron/eleven-orbital active space) and MP2-CAS methods are respectively used with the 6-311G(d, p) and 6-311++G(3df, 3pd) basis sets. The structure of the conical intersection that plays a prominent role in the photoisomerization of acrylonitrile is obtained. The intermediates and the transition structures of the ground states are also calculated, to allow a qualitative explanation of the reaction pathways. These model studies suggest that the preferred reaction route is: acrylonitrile -> Franck-Condon region -> conical intersection -> isoacrylonitrile -> transition state -> intermediate complex -> transition state -> cyanoacetylene. The theoretical evidence suggests that conical intersections found in this paper can give a better understanding of the photochemical reactions of acrylonitrile and support the experimental observations.