Predictive Modeling of Molecules of High-Energy Heterocyclic Compounds

DFT calculations at the B3LYP/6-311+G(2d,p) level and combined G4(MP2) and G4 methods within the GAUSSIAN-09 software package have been used to evaluate the standard enthalpies of formation of species in the gas phase (kJ/kg): C4N8O6 (2854.0), C4HN7O4 (2932.3), C4H2N6O2 (3104.8), C2N6O4 (4252.6), C2N8O4 (4395.9), C2N6O3 (4645.6), C2N8O4 (4755.2), C2HN7O2 (4815.7), C4N6O2 (5153.2), and C4N8O2 (5609.1). For experimentally studied compounds C2N6O4, C2N6O3, and C2N8O4, the $${{\Delta }_{f}}H_{{298}}^{^\circ }\left( {\text{g}} \right)$$ values calculated at the G4 level are 8–15% larger than the experimental values, which is almost half as large as the scatter of the experimental values for these compounds. The thermochemical data, IR absorption spectra, structural parameters, and atomic displacements for the strongest vibrations of high-energy compounds C4N8O6, C4HN7O4, C4H2N6O2, C2N8O4, C2HN7O2, C4N6O2, and C4N8O2 have been determined for the first time. It has been demonstrated that, for the compounds studied, the G4(MP2) and G4 computation levels give very close values (within 1–3%), which leads to significant saving in computational time (three- to eightfold). However, B3LYP/6-311+G(2d,p) calculations give values differing by 2–11% from the G4 values. The obtained data can be used as a reference and make it possible to distinguish the most promising groups of substances for operation as high-energy components of promising fuel.