Theoretical calculation and molecular design for high explosives: Theoretical study on polynitropyrazines and their N-oxides

The geometries of polynitropyrazines and their N-oxides have been fully optimized employing the density functional B3LYP method and the 6-31 + + G** basis set. For polynitropyrazines and their N-axides we have obtained the enthalpies of formation (at p = 1.013×10⁵Pa and T= 298.15 K) by designing isodesmic reactions and the detonation velocities by using the Stine method. Calculated results show that the aromaticity of the pyrazine ring of polynitropyrazine is lower than that of its N-oxide. From the acquired relationship between the experimental impact sensitivity H₅₀ (12B type) and the least C-NO₂ bond order the predicted H ₅₀ values for compounds 2,5-diamino-3,6-dinitropyrazine and 2,5-diamino-3,6-dinitropyrazine-1-oxide are 83 cm and 59 cm, respectively, implying that they are low sensitive explosives. The enthalpy of formation of polynitropyrazine is much less than that of its N-oxide. The calculated density (1.90 g/cm³) for 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) is close to the experimental value (1.918 g/cm³), and from both sensitivity and detonation velocity it has been deduced that LLM-105 is superior to other diaminodinitropyrazines and their N-oxides. The largest density and detonation velocity obtained in this work are 2.02 g/ cm³ (2-amino-3,5,6-trinitropyrazine) and 9.34 km/s (2,3,5,6-tetranitropyrazine), respectively.