AB-INITIO DENSITY-FUNCTIONAL COMPUTATIONS OF CONFORMATIONS AND BOND-DISSOCIATION ENERGIES FOR HEXAHYDRO-1,3,5-TRINITRO-1,3,5-TRIAZINE

Ab initio computations are described of the conformers and bond dissoc iation energies of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) with the Becke3-Lee-Yang-Parr (B3LYP) nonlocal density functional and the s tandard 6-31G and 6-311G** Gaussian basis sets. Five conformational m inima, closely spaced in energy, were located at the B3LYP/6-31G leve l of theory. The experimental gas-phase and solid-phase geometries for RDX are compared with the B3LYP/6-31G geometries. The rather short N -N bonds in the experimental crystal structure suggest that intermolec ular interactions lead to enhanced donation of the amine lone pair int o the nitro group in the solid state. The RDX nitrogen and carbon radi cals have key roles in thermal decomposition of RDX. The B3LYP/6-311G computed estimates for the N-NO2 and the C-H dissociation energies ( D-0) in RDX are respectively 42 and 85 kcal/mol. Compared with compute d N-NO2 and C-H bond strengths in related molecules, the bonds in RDX are rather weak. This suggests that initiation of decomposition by N-N cleavage and propagation of the decomposition by hydrogen atom transf ers should be facile.