The uB3LYP/6-311g++(d,p) method in the gas phase was used to simulate the reaction of ethylene with ortho, meta, para methylnitrobenzene, chloronitrobenzene, (CCl3)PhNO2, (CF3)PhNO2 in the T1 state, as well as determining the influence of the position of donor and acceptor substituents in the benzene ring on the activation energy of the reaction under study. It is established that during the reaction ethylene oxide and nitroso compound are formed.

DFT/B3PW91/6-31+G(d) method was used to study the reaction mechanism of alkynes with nitro compounds by the example of acetylene with HNO 2 , CH 3 NO 2 , and C 2 H 5 NO 2 .At the first stage, the interaction of HNO 2 in the T 1 state with acetylene 5takes place in the S 0 state.As a result of the reaction, a biradical compound (III) is formed. The spin density is concentrated at atoms O(6) and C(1), being 0.4759 and 0.9661, resp. The corresponding transition state is determined and shown in fig.(1).

The method uB3LYP/6-31g+(d) was used to simulate the reaction of photochemical oxidation of olefins such as etilene with nitrobenzene and HNO 2 in the triplet state. It is found that photooxidation occurs in two stages. In a first step complex formation of the nitro compound with an olefin has place and in the second step its further degradation to nitrosocompound and etilene oxide occurs. The energies of activation for each stage of the transformation were determined.

The method uB3LYP/6-31g+(d) was used to simulate the reaction of photochemical oxidation of olefins such as ethylene with orto-ClNO 2 Ph, para-ClNO 2 Ph in the triplet state. It is found that photooxidation of an olefin occurs in two stages. In the first step, the complex formation of the nitro compound with the olefin has place and in the second step its further transformation to nitrosocompound and ethylene oxide occurs. The activation energies for the first reaction of orto-ClNO 2 Ph with ethylene were 25.24 kcal mol -1 and for the second reaction of para-ClNO 2 Ph was 36.40 kcal mol -1 ..