Ab initio molecular orbital calculations have been performed at Hartree-Fock （HF）, second-order Mrller-Plesset （MP2）, and hybrid density functional theory （DFT） B3LYP levels with 6-31G^＊＊ basis set to investigate the low sensitive explosive trans-1,4,5,8-tetranitro-1,4,5,8- tetraazadecalin （TNAD） and its seven bicyclic isomers. Their molecular geometries, electronic structures, thermodynamic properties, and detonation performances were predicted and compared. The relationships between structures and various properties were discussed in detail. The calculated results agree well with the available experimental data, and suggest that some compounds may be novel potential candidates of high energy density materials （HEDMs） with performances better than TNT （2,4,6-trinitrotoluene） and similar to RDX （1,3,5-trinitro-1,3,5-triazacyclohexane）.
Density functional theory （DFT） has been employed to study the molecular geometries, electronic structures, infrared （IR） spectra, and thermodynamic properties of the high energy density compound hexanitrohexaazatricyclotetradecanedifuroxan （HHTTD） at the B3LYP/6-31G^＊＊ level of theory. The calculated results show that there are four conformational isomers （α, β, γ and δ） for HHTTD, and the relative stabilities of four conformers were assessed based on the calculated total energies and the energy-gaps between the frontier molecular orbitals. The computed harmonic vibrational frequencies are in reasonable agreement with the available experimental data. Thermodynamic properties derived from the IR spectra on the basis of statistical thermodynamic principles are linearly correlated with the temperature. Detonation performances were evaluated by using the Kamlet-Jacobs equations based on the calculated densities and heats of formation. It was found that four HHTTD isomers with the predicted densities of ca. 2 g·cm^-3, detonation velocities near 10 km·s^-1, and detonation pressures over 45 GPa, may be novel potential candidates of high energy density materials （HEDM）. These results may provide basic information for the molecular design of HEDM.
Density functional theory (DFT) method has been employed to study the effect of nitroamino group as a substituent in cyclopentane and cyclohexane, which usually construct the polycyclic or caged nitra-mines. Molecular structures were investigated at the B3LYP/6-31G** level, and isodesmic reactions were designed for calculating the group interactions. The results show that the group interactions ac-cord with the group additivity, increasing with the increasing number of nitroamino groups. The dis-tance between substituents influences the interactions. Detonation performances were evaluated by the Kamlet-Jacobs equations based on the predicted densities and heats of formation, while thermal stability and pyrolysis mechanism were studied by the computations of bond dissociation energy (BDE). It is found that the contributions of nitroamino groups to the detonation heat, detonation velocity, detonation pressure, and stability all deviate from the group additivity. Only 3a, 3b, and 9a-9c may be novel potential candidates of high energy density materials (HEDMs) according to the quantitative cri-teria of HEDM (ρ≈ 1.9 g/cm3, D ≈ 9.0 km/s, P ≈ 40.0 GPa). Stability decreases with the increasing number of N-NO2 groups, and homolysis of N-NO2 bond is the initial step in the thermolysis of the title com-pounds. Coupled with the demand of thermal stability (BDE > 20 kcal/mol), only 1,2,4-trinitrotriazacy-clohexane and 1,2,4,5-tetranitrotetraazacyclohexane are suggested as feasible energetic materials. These results may provide basic information for the molecular design of HEDMs.
Science in China Series B-Chemistry (Sci China Ser B-Chem) is a monthly peer-reviewed academic journal su-pervised by the Chinese Academy of Sciences, and co-sponsored by the Chinese Academy of Sciences and National Natural Science Foundation of China. Its primary mission is to encourage communication of basic and inno-vative research results of high quality in the fields of chem-istry. The subject areas featured include theoretical chemis-try, physical chemistry, organic chemistry, inorganic chemis-try, polymer chemistry, biological chemistry, environmental chemistry, and chemical engineering, etc. All papers should be intelligible for a broad scientific audience.
