A possible crystal volume factor in the impact sensitivities of some energetic compounds

Abstract

We have investigated the possibility of a link between the impact sensitivities of energetic compounds and the space available to their molecules in their crystal lattices. As a measure of this space, we use ΔV=V_eff−V(0.002), where V_eff is the effective molecular volume obtained from the crystal density and V(0.002) is that enclosed by the 0.002 au contour of the molecule’s gas phase electronic density, determined computationally. When experimental impact sensitivity was plotted against ΔV for a series of 20 compounds, the nitramines formed a separate group showing little dependence upon ΔV. Their impact sensitivities correlate well with an anomalous imbalance in the electrostatic potentials on their molecular surfaces, which is characteristic of energetic compounds in general. The imbalance is symptomatic of the weakness of the N–NO₂ bonds, caused by depletion of electronic charge. The impact sensitivities of non-nitramines, on the other hand, depend much more strongly upon ΔV, and can be quite effectively related to it if an electrostatically-based correction term is included. Figure Measured impact sensitivities (h ₅₀) plotted against computed ΔV for the compounds in Table 1. Triangles correspond to nitramines, circles to all others