Abstract <p>The transfer of one of the oxygen atoms of nitro compound molecules in the <i>T</i>₁ state to one of the nitrogen atoms of unsymmetrical dimethylhydrazine molecule in the <i>S</i>₀ state has been studied using the B3LYP/6-311G+(d) quantum chemical method. This process is one of the possible routes for photochemical oxidation of nitrogen-containing compounds by nitro compounds. Two possible reaction variants with attack on the N-dimethyl nitrogen atom (1) and the nitrogen atom of the hydrazine group (2) have been considered. Quantum chemical calculations show that such reactions are possible due to relatively low Gibbs energy. The corresponding values lie in the range of 99–111 kJ/mol for reaction (1) and 136–123 kJ/mol for reaction (2). Calculations of spin densities on atoms in the transition state show that there is no significant change in the distribution of spin density on the atoms of the reaction center. The obtained data may indicate a biradical character of the process. It has been concluded that the oxygen transfer reaction to the nitrogen atom with dimethyl substituents is energetically more favorable.</p>