A quantum mechanical investigation of the relation between impact sensitivity and the charge distribution in energetic molecules

Quantum mechanically determined electrostatic potentials for isosurfaces of electron density of a variety of CHNO explosive molecules are analyzed to identify features that are indicative of sensitivity to impact. This paper describes the development of models for prediction of impact sensitivity of CHNO explosives using approximations to the electrostatic potentials at bond midpoints, statistical parameters of these surface potentials, and the generalized interaction properties function [J. S. Murray, T. Brinck, P. Lane, K. Paulsen and P. Pulitzer, J. Mol. Struct (THEOCHEM) 1994, 307, 55] or calculated heats of detonation. The models are parametrized using a set of 34 polynitroaromatic and benzofuroxan explosives for which impact sensitivity measurements exist. The models are then applied to a test set of 15 CHNO explosives from a variety of chemical families in order to assess the predictive capability of the models. Patterns of the surface potentials of the molecules examined in this study suggest that the level of sensitivity to impact is related to the degree of positive charge buildup over covalent bonds within the inner framework of these explosives. The highly sensitive explosives show large positive charge buildup localized over covalent bonding regions of the molecular structures, whereas the insensitive explosives do not exhibit this feature. For the nitroaromatic and benzofuroxan compounds, sensitivity appears to be related to the degree and distribution of positive charge build-up localized over the aromatic ring or over the C-NO2 bonds.