Quantum chemical study on nitroimidazole, polynitroimidazole and their methyl derivatives

The insensitive explosive candidates, nitroimidazoles, polynitroimidazoles and their methyl derivatives, are investigated using density functional theory (DFT). The homolytic bond dissociation energies (BDEs) corresponding to -NO2 group removal from carbon or nitrogen site on imidazole ring were calculated at B3P86/6-311G** level, and the weakest bond has been determined. Further, a correlation is developed between impact sensitivity h50 and the ratio (BDE/E) of the weakest bond BDE to the total energy E, and we extrapolate this relationship to predict the impact sensitivities for compounds where experiments are not available. It is found that most of the title compounds are insensitive towards impact stimuli with their h50 larger than 60.0 cm. Heats of formation (HOFs) for the 21 title compounds at 298 K in gas are also determined both at B3LYP/6-311G** and B3P86/6-311G** levels using isodesmic work reactions. The calculated BDEs and HOFs consistently indicate that C-nitro-substituted imdazole is more stable than the corresponding N-substituted one, and the introduction of methyl on C increases the stability whereas the methyl attached to N atom decreases the stability.