How Do the Surroundings of the C-NO2 Fragment Affect the Mechanical Sensitivity of Trinitroaromatic Molecules? Evidence from Crystal Structures and Ab Initio Calculations

The dissociation of the C-NO2 bond is the initial step in the process of the detonation of nitroaromatic explosives. The strength of the C-NO2 bond is significantly influenced by the relative position of the nitro group with respect to the aromatic ring plane since the planar arrangement enables the delocalization of electron density, which strengthens this bond. In this study, we have combined a statistical analysis of geometrical parameters extracted from crystal structures of trinitroaromatic molecules with ab initio calculations of non-covalent index plots and Wiberg bond index values for selected trinitroaromatic molecules to elucidate the influence of nearby substituents on the relative position of nitro groups with respect to the aromatic ring plane. The results of the analysis showed that neighboring substituents have a significant impact on the geometry of nitro groups. The results also showed that this influence arises from the repulsive interaction of voluminous substituents, attractive non-covalent contacts, and the electronic effects of substituents.