Ab initio study on the mechanism of the reactions of the nitrate radical with haloalkenes: 1,2-dichloroethene, 1,1-dichloroethene, trichloroethene, and tetrachloroethene

A general mechanism for the reactions of the NO3 radical with 1,2-dichloroe thene, 1,1-dichloroethene, trichloroethene, and tetrachloroethene is propos ed from ab initio DFT calculations. The calculated mechanism shows three ma in parallel reaction pathways. For the systems where the two carbon atoms a re differently substituted, the study includes both the attacks with Markow nikoff and contra-Markownikoff orientation. The first reaction pathway lead s to the formation of an epoxide along with the NO2 radical, the second one to the formation of carbonyl compounds, and the third one leads, through t he cleavage of the C-C bond, to the formation of carbonyl compounds with a lower number of carbon atoms. The stationary points on the potential energy surface (PES) were found by means of density functional theory (DFT) calcu lations with the B3LYP functional and the 6-31G* basis set. for each statio nary point, the geometry was optimized and the obtained conformation was ch aracterized as an equilibrium structure (reactant, product, or intermediate ) or transition state structure.