A theoretical study of polynitropyridines and their N -oxides

The geometries of polynitropyridines and their N-oxides have been optimized using the B3LYP density functional method and the 6-311++G**basis set. The accurate gas phase enthalpy of formation (at p = 1.013 × 10 5 Pa and T = 298.15 K) for pyridine and its N-oxide has been calculated employing the G3(MP2) method and the atomization scheme, and for polynitropyridines and their N-oxides at the B3LYP/6-311++G**level by designing the isodesmic reactions in which the pyridine ring maintains integral. Based on B3LYP/6-311++G**optimized geometries and calculated natural charges, this paper has calculated the crystal structures by the Karfunkel-Gdanitz method, and based on estimated solid enthalpies of formation and crystal densities has predicted the Chapman-Jouguet detonation velocities (D CJ ) by the Stine method. Calculated results show that for polynitropyridines and their N-oxides the introduction of NH 2 groups increases the strength of CNO 2 bonds but reduces the gas phase enthalpy of formation. The least CNO 2 bond order indicates that compounds 3,5-diamino-2,4,6-trinitropyridine and its N-oxide, whose D CJ values are predicted to be approximately 8.2 and 8.6 km/s, respectively, are most possibly low-sensitive or insensitive energetic materials. The largest D CJ value obtained in polynitropyridines and their N-oxides is about 9.5 km/s.