Effect of chlorine atoms in chlorinated ethylene on the rate and mechanism of its reaction with ozone (original) (raw)

2010, Russian Journal of Physical Chemistry B

The UQCISD, UB3LYP, UMP2, and MRMP2 methods in conjunction with the 6 31+G**/6 311+G** and aug cc PVDZ basis sets are used to study the primary reaction of ozone with chlorinated eth ylene derivatives: tetrachloroethylene, trichloroethylene, 1,2 trans dichloroethylene, 1,2 cis dichloroethyl ene, 1,1 dichloroethylene, and chloroethylene. The reaction is studied for both concerted and nonconcerted ozone addition. The UB3LYP DFT method in conjunction with the 6 31+G** basis set is used to examine various modes of addition of ozone to these chlorinated ethylenes by the Criegee and DeMore mechanisms. The geometry and energy of the transition states, the enthalpy and entropy, and the rate constants and ratios thereof for all the reactions are calculated. The UB3LYP method generally satisfactorily describes the two reaction pathways and, largely correctly predicts the rate constants, in agreement with the available experi mental data. At the same time, this method appears to be inapplicable to modeling the interaction of ozone with 1,1 dichloroethylene. In this case, the single determinant approximation turns out to be unsuitable, and, therefore, MCSCF methods should be used. The MRMP2 method yields reasonable values of the rate constants for the DeMore mechanism, whereas in the case of the Criegee mechanism, the MP2 method does well. The UB3LYP/6 31+G** and UQCISD/aug cc PVDZ methods give similar values of the ratio between the rate constants for the two pathways, a result that demonstrates the versatility of the first one.