Ab initio study on the mechanism of tropospheric reactions of the nitrate radical with haloalkenes: Chloroethene

A mechanism for the reaction of the Nb radical with vinyl chloride is propo sed on the basis of B3LYP and CASSCF quantum chemistry calculations. Two in itial transition states lead to the Markownikoff and contra-Markownikoff ad dition of NO3 to chloroethene. From: the two initial adducts different inte rconnected pathways start. We have found epoxichloroethane, chloroethanal, nitrous acid, acetyl chloride, nitric acid, formaldehyde, formyl chloride, and NO radical as main products.,The energy of the reactants, products,nd a ll intermediates along with the barrier heights for each reaction path has been calculated. The: geometry optimization and characterization of all of the stationary points found on the potential energy hypersurface was made a t the B3LYP level with a 6-31G* basis set, and some of the stationary point s have been reoptimized with the 6-311+G* basis set. Later, single-point CA SSCF calculations were carried out with the same basis set, building the ac tive; space with Seven active electrons in eight active orbitals. It can be concluded that an equilibrium distribution of formyl chloride, :formaldehy de; and the NO radical will:,be obtained along with small proportions of ep oxychloroetane and the Markownikoff radical adduct. An estimation of the re action rate constant has also been calculated.