Understanding of the difference in packing density of some energetic isomers

Abstract

Energetic isomerism has not received enough attention and it in fact occurs rather commonly in the field of energetic materials. A series of energetic isomers possess the same molecular formulation but different molecular structures and possibly significant differences in performances and properties. Packing density is one of the most decisive factors for detonation properties of energetic materials. This work focuses upon the difference in packing density of energetic isomers and the related underlying mechanism. Structurally, the presence of CH₃/CH₃/CH and catenated N/O chains generally causes low molecular density, while that of intramolecular hydrogen bonding and NH₂ linked by conjugated rings does the opposite; and the strong intermolecular hydrogen bonding facilitates a high packing coefficient. Largely, it exhibits that, for a group of energetic isomers, the packing coefficient rather than molecular density dominates packing density. Sometimes, an isomer with the lowest total energy and the strongest trigger bond can possess the highest detonation velocity, suggesting that the most stable isomer may be the most powerful. It shows that the understanding of the difference in packing density of energetic isomers can serve as a strategy for constructing high energy and low sensitivity molecules.