Molecular Design And Theoretical Study On Organic Cage Compounds

Cage compounds such as hexanitrohexaazaisowurtzitane (CL-20) and octanitrocubane (ONC) have drawn a great deal of attention due to their excellent properties and attracted many research interests for new cage compounds.In this thesis, computational methods, especially density functional theory (DFT) of quantum chemistry and molecular mechanics (MM) have been employed to study a series of new designed cage compounds systematically from gas phase to crystalline. Contents include:1. A series of cage structures were designed including the derivatives of CL-20, N12, and2,4,6,8,10,12,13-heptaazatetracyclo [5.5.1.03,11.05,9] tridecane, and the hybrid derivatives of TATB and nitrocubane. Investigations on the structures and properties were carried out.The effects of substituents (nitro groups) on the total energy(Eo), zero point energy(ZPE), and bond length were studied. With the increasing number of nitro groups, E0and ZPE decrease, C-NO2and C-C bonds were lengthened, and C-H bond was shortened. A large gap usually found for nonmetallic compounds exists between the conduction (unoccupied crystal orbitals) and valence (occupied crystal orbitals) bands. This indicates that the compounds were stable. Analysis of density of state (DOS) and partial density of state (PDOS) showed that the N-NO2bond acts as an active center and may be the initial breaking bond in the thermal pyrolysis steps.2. The simulated IR spectra were obtained based on the scaled harmonic vibrational frequencies by0.96. The characteristic bands were analyzed and discussed.3. On the basis of the statistical thermodynamics principle, thermodynamic properties of the cage compounds in gas and solid state including standard molar heat capacity, standard molar entropy, and standard molar thermal enthalpy were evaluated. All of them increase with the increasing of temperature and the number of nitro groups.4. The heats of formation (HOFs) of the cage compounds were evaluated via designed reactions and the relationships between the structure and HOFs were discussed. The effect of nitro groups on the HOF is the results of both repulsion and superconjugation from nitro groups. When the number of nitro groups is small, the superconjugation effect of nitro groups can stabilize the cage skeleton. However, when there are more than three nitro groups on the skeleton, the repulsion energy strengthens and leads to the increase in the total energy and HOF.5. Strain energies (SEs) were estimated via the designed isodesmic reactions and the effects of substituents on the cage were discussed. Results indicate that the compounds linked with the electron-donating group have larger SEs than that with electron-withdrawing group.6. The detonation parameters were calculated using Kamlet-Jacobs equations and Stine equation. Results indicate that the data obtained from the former are more reliable and the cage compounds have good detonation performance. It is noticed that density p, detonation velocity D, and detonation pressure P increase with the increasing number of nitro groups.7. Bond dissociation energies (BDEs) were calculated. Results indicate that beside the N-NO2bond C-C and C-N bonds in the cage may also be the trigger bonds due to the cage strain. BDEs of all cage compounds are larger than150kJ·mol-1, with most of them being larger than200or even300kJ·mol-1, indicating that all the compounds designed in this thesis have good thermal stabilities.