DFT studies on trinitromethyl- or dinitromethyl-modified derivatives of RDX and β-HMX

The heats of formation (HOFs), energetic properties, strain energies, thermal stability, and impact sensitivity for a series of trinitromethyl- or dinitromethyl-modified RDX and β-HMX derivatives were studied by using density functional theory. It is found that the introduction of trinitromethyl group is an effective structural unit for improving the HOFs and energetic properties of the derivatives. However, incorporating the dinitromethyl group into the parent compound is not favorable for increasing its HOF and detonation properties. The effects of trinitromethyl or dinitromethyl groups on the stability of the parent compound are discussed. An analysis of the bond dissociation energies for several relatively weak bonds suggests that the substitution of the trinitromethyl or dinitromethyl group decreases the thermal stability of the derivatives. On the whole, the C-NO₂ bond in the trinitromethyl or dinitromethyl group is the weakest one and the C-NO₂ cleavage may happen in thermal decomposition. The introduction of the trinitromethyl or dinitromethyl group increases the impact sensitivities of the derivatives. In addition, the introduction of trinitromethyl group intensifies the strain of the central ring for the title compounds, while the effects of the dinitromethyl groups on the strain of the central ring are coupled to those of the ring structures.