A mechanism for the reaction of the NO 3 radical with propene is proposed on the basis of B3LYP and CASSCF calculations. The mechanism involves initially both Markownikoff and contra-Markownikoff oriented addition on the double bond. From the initial radical adducts several interconnected pathways have been found, giving 1,2-epoxypropane, propanal, propenol, propanone, formaldehyde, ethanal, NO, and NO 2 . The geometries of the stationary points found on the potential energy hypersurface (PES) were obtained and characterized by means of density functional theory (DFT) B3LYP/6-31G* calculations. Comparison of the optimized geometries on a limited number of molecular structures was carried out with calculations at the CASSCF level of theory with the same basis set, building the active space with five electrons in six orbitals.

A mechanism for the reaction of the NO 3 radical with vinyl chloride is proposed on the basis of B3LYP and CASSCF quantum chemistry calculations. Two initial transition states lead to the Markownikoff and contra-Markownikoff addition of NO 3 to chloroethene. From the two initial adducts different interconnected 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, and all 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 at the B3LYP level with a 6-31G* basis set, and some of the stationary points have been reoptimized with the 6-311+G* basis set. Later, single-point CASSCF calculations were carried out with the same basis set, building the active space with seven active electrons in eight active orbitals. It can be concluded that an equilibrium distribution of formyl chloride, formaldehyde, and the NO radical will be obtained along with small proportions of epoxychloroetane and the Markownikoff radical adduct. An estimation of the reaction rate constant has also been calculated.

A general mechanism for the reactions of the NO3 radical with 2-butene, isobutene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene is proposed on the basis of density functional theory (DFT) calculations. This mechanism is compared with previously reported model experimental kinetic studies at low pressures and temperatures in anaerobic conditions. In our theoretical proposal of mechanism, the initial step is the addition of the NO3 radical to the double bond. For the systems showing different substitution on both sides of the double bond, two adducts have been obtained, one following the Markovnikov rule and the other with the anti-Markovnikov orientation. Starting from the adduct we have found that three main reaction pathways follow. The first one leads to epoxide and NO2 formation, the second to carbonyl compounds, and the third, through the cleavage of the C−C bond, to carbonyl compounds with a lower number of carbon atoms than the original substrate and NO. The theoretical proposal of mechanism leads to the following products:  (a) for 2-butene, 2,3-dimethyloxirane, butanone, and ethanal; (b) for isobutene, 2-methylepoxypropane, 2-methylpropanal, butanone, propanone, and formaldehyde; (c) for 2-methyl-2-butene, 2-methylepoxybutane, 3-methylbutanone, propanone, 2-dimethylpropanal, and ethanal; (d) for 2,3-dimethyl-2-butene, 2,3-dimethylepoxybutane, 3-dimethylbutanone, and propanone. In all cases, NO2 and NO are also obtained as products. The geometry of all the involved stationary points in the potential energy hypersurface has been optimized at the DFT level with the B3LYP functional and a 6-31G* basis set. All these conformations were characterized at the same calculation level.

A general mechanism for the reactions of the NO 3 radical with 1,2-dichloroethene, 1,1-dichloroethene, trichloroethene, and tetrachloroethene is proposed from ab initio DFT calculations. The calculated mechanism shows three main parallel reaction pathways. For the systems where the two carbon atoms are differently substituted, the study includes both the attacks with Markownikoff and contra-Markownikoff orientation. The first reaction pathway leads to the formation of an epoxide along with the NO 2 radical, the second one to the formation of carbonyl compounds, and the third one leads, through the 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) calculations with the B3LYP functional and the 6-31G* basis set. For each stationary point, the geometry was optimized and the obtained conformation was characterized as an equilibrium structure (reactant, product, or intermediate) or transition state structure.

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