Polynitrohexaazaadamantanes (PNHAAs) have been the subject of much recent research because of their potential as high energy density materials (HEDMs). The B3LYP/6-31G method was employed to evaluate the heats of formation (HOFs) for PNHAAs by designing isodesmic reactions. The HOFs are found to be correlative with the number (n) and the space orientations of nitro groups. Detonation velocities (D) and detonation pressures (P) were estimated for PNHAAs by using the well-known Kamlet-Jacobs equations, based on the theoretical densities (rho) and HOFs. It is found that D and P increase as n ranges from 1 to 6, and PNHAAs with 4-6 nitro groups meet the criteria of an HEDM. When n is over 6, rho of PNHAAs slightly increases; however, the chemical energy of detonation (Q) decreases so greatly that both D and P decrease. The calculations on bond dissociation energies suggest that the N-N bond be the trigger bond during the pyrolysis initiation process of each PNHAA, and with increasing n, N-N bond dissociation energy (E(N-N)) decreases on the whole, that is to say, the relative stability of PNHAAs decreases. All E(N-N)(s) of PNHAAs are more than 30 kcal.mol(-1), which further proves that four PNHAAs with 4-6 nitro groups can be used as the candidates of HEDMs. Considering the synthesis difficulty and the performance as an energetic compound, we finally recommended 2,4,6,8,10-pentanitrohexaazaadamantane as the target HEDM for PNHAAs.

Density function theory (DFT) has been employed to study the geometric and electronic structures of a series of spiro nitramines at the B3LYP/6-31G level. The calculated results agree reasonably with available experimental data. Thermodynamic properties derived from the infrared spectra on the basis of statistical thermodynamic principles are linearly correlated with the number of nitramine groups as well as the temperature. Detonation performances were evaluated by the Kamlet-Jacobs equations based on the calculated densities and heats of formation. It is found that some compounds with the predicted densities of ca. 1.9 g/cm3, detonation velocities over 9 km/s, and detonation pressures of about 39 GPa (some even over 40 GPa) may be novel potential candidates of high energy density materials (HEDMs). Thermal stability and the pyrolysis mechanism of the title compounds were investigated by calculating the bond dissociation energies (BDE) at the B3LYP/6-31G level and the activation energies (E(a)) with the selected PM3 semiempirical molecular orbital (MO) based on the unrestricted Hartree-Fock model. The relationships between BDE, E(a), and the electronic structures of the spiro nitramines were discussed in detail. Thermal stabilities and decomposition mechanisms of the title compounds derived from the B3LYP/6-31G BDE and the UHF-PM3 E(a) are basically consistent. Considering the thermal stability, TNSHe (tetranitrotetraazaspirohexane), TNSH (tetranitrotetraazaspiroheptane), and TNSO (tetranitrotetraazaspirooctane) are recommended as the preferred candidates of HEDMs. These results may provide basic information for the molecular design of HEDMs.

Polynitro cage compound 4-trinitroethyl-2,6,8,10,12-pentanitrohexaazaisowurtzitane has the same framework with but higher stability than CL-20 and is a potential new high energy density compound (HEDC). In this paper, the B3LYP/6-31G(d,p) method of density functional theory (DFT) has been used to study its heat of formation, IR spectrum, and thermodynamic properties. The stability of the compound was evaluated by the bond dissociation energies. The calculated results show that the first step of pyrolysis is the rupture of the N-NO(2) bond in the side chain and verify the experimental observation that the title compound has better stability than CL-20. The crystal structure obtained by molecular mechanics belongs to the P2(1)2(1)2(1) space group, with lattice parameters a = 12.59 Å, b = 10.52 Å, c = 12.89 Å, Z = 4, and ρ = 2.165 g·cm(-3). Both the detonation velocity of 9.767 km·s(-1) and the detonation pressure of 45.191 GPa estimated using the Kamlet-Jacobs equation are better than those of CL-20. Considering that this cage compound has a better detonation performance and stability than CL-20, it may be a superior HEDC.