Mechanism of the first step of ozone addition to halogen-substituted ethylenes

Abstract

Quantum chemical calculations have been carried out for the ozonolysis of monofluoro-, monochloro-, 1,1-difluoro-, and 1,1-dichloroethylene using the aug-cc-pVDZ basis set by the B2PLYP (B2LYP-D) double-hybrid method involving the Moller-Plesset perturbation theory, the CASSCF multiconfigurational ab initio method with MRMP2 corrections, and the CCSD coupled cluster method. The mechanisms of concerted (Criegee) and nonconcerted (DeMore) additions have been investigated. The CCSD method more precisely simulates these reactions. With the MRMP2 method, the overall reaction rate constant is underestimated because of incomplete geometry optimization, but on the whole the dependence of the rate constant on the nature and number of substituents is practically identical to the dependence predicted by the two other methods. Polar substituents in the molecule increase the contribution from the nonconcerted addition mechanism, which reaches 50% for 1,1-difluoroethylene and 98% for 1,1-dischloroethylene.