Can the sensitivity of energetic materials be tuned by using hydrogen bonds? Another look at the role of hydrogen bonding in the design of high energetic compounds.

Strongly positive electrostatic potential in the central areas of molecules of energetic materials is one of the most important factors that determines the sensitivity of these molecules towards detonation. Quantum chemical and density functional theory calculations were used to reveal the influence of hydrogen bonding on the values of electrostatic potential above the central areas of molecules of three conventional explosives: 1,3,5-trinitrobenzene, 2,4,6-trinitrophenol, and 2,4,6-trinitrotoluene. Both the case when energetic molecules act as hydrogen atom donors and when they act as hydrogen atom acceptors were considered. Results of the calculations performed using the M06/cc-PVDZ level of theory showed that there are significant differences in the influence of hydrogen bonding on the electrostatic potential of energetic molecules acting as hydrogen atom donors and hydrogen atom acceptors. In the case when energetic molecules act as hydrogen acceptors, an increase of 10% in the strength of positive electrostatic potential was identified. In the case when energetic molecules act as hydrogen atom donors, a significant decrease (20-25%) in the strength of the positive potential on the molecular surface was calculated. These differences give an opportunity for fine-tuning the impact sensitivities of energetic compounds and provide new guidelines for the design of explosives with desirable characteristics.

How aromatic system size affects the sensitivities of highly energetic molecules?

Positive values of electrostatic potentials above the central regions of the molecular surface are strongly related to the high sensitivities of highly energetic molecules. The influence of aromatic system size on the positive values of electrostatic potentials and bond dissociation energies of C-NO2 bonds was studied by Density Functional Theory (DFT) calculations on a series of polycyclic nitroaromatic molecules. Calculations performed at PBE/6-311G** level showed that with the increase of the aromatic system size, values of positive electrostatic potential above the central areas of selected energetic molecules decrease from 32.78 kcal mol-1 (1,2,4,5-tetranitrobenzene) to 15.28 kcal mol-1 (2,3,9,10-tetranitropentacene) leading to the decrease in the sensitivities of these molecules towards detonation. Results of the analysis of electrostatic potential maps were in agreement with the trends in bond dissociation energies calculated for C-NO2 bonds of studied nitroaromatic molecules. Bond dissociation energies values indicate that the C-NO2 bond in the molecule of 1,2,4,5-tetranitrobenzene (56.72 kcal mol-1) is weaker compared to the nitroaromatic molecules with the additional condensed aromatic rings and with a similar arrangement of -NO2 groups (59.75 kcal mol-1 in the case of 2,3,9,10-tetranitropentacene). The influence of the mutual arrangement of -NO2 groups on the sensitivity of nitroaromatic molecules was also analyzed. Results obtained within this study could be of great importance for the development of new classes of highly energetic molecules with lower sensitivity towards detonation.