Computational study of substituted 2,2′-bi-1H-imidazole as high energetic materials

Abstract

Density functional theory (DFT) calculations were performed for a series of 2,2′-bi-1H-imidazole derivatives. The B3LYP and B3P86 functionals with 6-311G ∗∗ basis set were used. The heats of formation (HOFs) were predicted through designed isodesmic reactions. Calculated results show that the HOFs decrease as the –NO 2 groups being replaced by –NF 2, but the HOFs increase as the –NO 2 groups being replaced by –N 3. When the –NO 2 groups are replaced by –NH 2, the HOFs initially decrease then increase. As for the isomeric compounds, the HOFs decrease following the increase of the number of hydrogen bonds for the different substituent position. At B3LYP/6-311G ∗∗ level, the HOF of 4,4′-diamino-5,5′-dinitro-2,2′-bi-1H-imidazole is the smallest (125.2 kJ/mol), and the HOF of 4,4′,5,5′-tetraazido-2,2′-bi-1H-imidazole is the largest (1608.9 kJ/mol). The magnitudes of intramolecular group interactions were predicted through the disproportionation energies. The E disproportion of 4,4′-diamino-5,5′-dinitro-2,2′-bi-1H-imidazole is −70.3 kJ/mol and is the smallest among the title compounds, but that of 4,4′,5,5′-tetranitro-2,2′-bi-1H-imidazole is the largest, which is 128.1 kJ/mol. Thermal stabilities were evaluated via bond dissociation energies (BDE) at the UB3LYP/6-311G ∗∗ level. The BDE ZPE value for C–NO 2 bond, 270.0 kJ/mol in average, is the smallest compared to other types of bonds.