Competition between the Concerted and Nonconcerted Addition of Ozone to a Double Bond

摘要

Quantum chemistry methods are used to investigate the mechanism of the reaction of ozone with the double bond of ethylene. It is shown that there are two possible reaction mechanism; concerted addition through a symmetrical transition state (Criegee mechanism) and nonconcerted addition through a biradical transition state (DeMore mechanism). In the single-determinant approximation, both mechanisms were described by using the QCISD, CCSD, and B3LYP methods. These methods give a reasonable ratio between the rates of the two reaction channels, with the rate constants being closer to the experiment when calculated by the CCSD and B3LYP methods. Multiconfiguration calculations are performed at the MRMP2 level. They also show the presence of both channels of the reaction and yield reasonable values of the rate constants for reaction channels and the ratio thereof. It is shown that the reaction of ethylene with ozone via the con-certed addition mechanism is much faster.