Theoretical design of bicyclo[2.2.1]heptane derivatives for high-energy density compounds with low impact sensitivity

For new high-energy density compounds, a series of new bicyclo[2.2.1]heptane derivatives were designed and studied by density functional theory (DFT) method. The heat of formation (HOF) was evaluated by the isodesmic reaction. The densities and the heats of sublimation were predicted by the electrostatic potential analysis at B3PW91/6-31G(d,p) and B3LYP/6-311++G(2df,2p) levels, respectively. The detonation performances were predicted by the Kamlet-Jacobs equations. The bond dissociation energies (BDE) and impact sensitivity that is evaluated by the free space per molecule were also studied to give a better understanding of the stability. Results show that HOFs increase with the increasing number of N atoms. When the number of NO2 groups is larger than 4, HOFs generally increase with the increasing number of NO2 groups. Even though solid-phase HOF is decreasing, detonation energy is always rising with Oxygen Balance (OB) closing to zero-OB, and positive value of OB will largely reduce detonation energy. Detonation velocity and detonation pressure of the designed compounds are in the range of 5.62–9.46 km/s and 11.72–41.44 GPa, respectively. And detonation velocity and detonation pressure always increase with the increasing number of N atoms or NO2 groups except when OB is positive value. BDEs of all designed compounds are larger than 20 kcal/mol shows that all designed compounds have a reasonable thermal stability. The calculated impact sensitivities show that all designed HEDCs have acceptable sensitivity. Especially impact sensitivity of C7, D7, E7, F6 and G6 are expected to be very close to Tetryl (h50 = 25 cm). Considering the thermal stability, impact sensitivity and detonation performance, A8, B8, C7, C8, D7, E7, F6 and G6 might be interesting candidates for use as HEDCs.