Trigger bond analysis of azo‐based energetic materials

Abstract

Azo-based energetic materials may initiate explosive decomposition by extruding molecular nitrogen to produce radical fragments. Density functional theory and Wiberg bond index analysis were used to determine trends in bond strength for a series of aromatic azo compounds. Interactions between ortho ring hydrogens and an azo nitrogen lone pair favor a planar molecule with a strengthened azo linkage. Steric groups substituted ortho to the azo linkage cause the molecule to twist, which disrupts delocalization of the π density and weakens the CNazo bond. The results of this study are generally consistent with the low sensitivity of various aromatic azo-based energetic materials. Discrepancies between calculated bond strengths and the experimental impact sensitivities could be attributed to packing forces that affect molecular planarity in the solid state.