The search for the optimal level of theory has been performed to achieve the best correspondence of calculated values and experimental results for further quantum-chemical modeling of systems compoused from sulphides and organic nitrocompounds in the triplet state. The reaction: HS + NO2 → HSO + NO was selected as the model reaction. The standard enthalpy of this reaction calculated theoretically was compared with its experimental value known from literature. Such theories as DFT, UHF and ROHF and the following basis sets: 6-31++G**, 6-311++G**, aug-cc-pVDZ, were used for computations. XC functionals for DFT calculations are the following: b3lyp, bhlyp, pbe0, xpbe96_cpbe96.