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).