Molecular Design And Performance Predictions Of High-nitrogen Energetic Compounds

High-nitrogen energetic compounds as the fourth generation of high-energy density materials (HEDM) have potential applications such as gas generating agents, propellants, smoke-free pyrotechnic fuels, high explosives and so on. In recent years, the high-nitrogen energetic compounds have gradually become a hot research owing to their high density, high positive heat of formation (HOF), high detonation performance, and good thermal stability. Theoretical studies on their structure-property relations are very necessary and important for molecular design on high-energy density compounds (HEDC).In this thesis, density functional theory (DFT) was used to study the geometric structures, electronic structures, densities, HOFs, thermal stability, and detonation properties of different types of a series of high-nitrogen energetic compounds. The HOFs of 57 azo compounds (including nitrogen-containing methyl-substituted molecules, amino-substituted molecules, and heterocycles) were calculated by using six high-level theoretical models via the atomization scheme. According to the criteria of detonation performance and thermal stability, the potential candidates of HEDC were selected. The contents of the dissertation can be divided mainly into three parts:In the first part, the HOFs of 57 azo compounds were calculated by using Hartree-fock (HF), DFT, and six high-level theoretical models including variants of Gaussian-n (Gn:G2, G2(MP2), and G3) and complete basis set (CBS-n:CBS-4M, CBS-Q, and CBS-QB3). The G2 model presents the most accurate HOFs among the six high-level models, followed by the G2(MP2) and CBS-QB3. The CBS-Q model consistently gives more accurate HOFs than the G2 or G2(MP2) for the compounds with -NO2. However, the case is quite the contrary for the compounds with -NH2,-NH-, or-CN. Overall, the six high-level models may be more suitable for predicting the HOFs of the aromatic compounds. The CBS-Q or G2(MP2) model is a compromise between computation efficiency and accuracy for predicting the HOFs of the 57 azo compounds.In the second part, we reported a systematic study on the HOFs, thermal stability, and energetic properties of a series of 1,2,4,5-tetrazine derivatives (single ring) by using DFT. First, the HOFs of five 1,2,4,5-tetrazine derivatives (whose experimental values are available) were calculated using different methods via designed isodesmic reactions and the reliability of the methods (HF, DFT, M(?)ller-Plesset (MP2), and semiempirical methods) was checked. Second, the HOFs of seventeen 1,2,4,5-tetrazine derivatives were predicted at the DFT-B3P86 level with 6-311G** basis set. Then, their thermal stabilities were evaluated based on their bond dissociation energies. Finally, their detonation velocities and pressures were predicted by the calculated HOFs and densities. According to the detonation performance and thermal stability, three 1,2,4,5-tetrazine derivatives may be regarded as the potential candidates of HEDC.In the third part, the HOFs, thermal stability, and energetic properties of a series of TETZ, TTZ,3,3’-azobis-1,2,4,5-tetrazine, C,C’-azobis-triazole, N,N’-azobis-triazole, ATT derivatives, and nitrogen-bridged 1,2,4,5-tetrazine-, furazan-, and 1H-tetrzole-based polyheterocyclic compounds were studied systematically by using DFT. Their HOFs were calculated by designing isodesmic reactions. Next their thermal stabilities were evaluated based on their bond dissociation energies. Finally their detonation velocities and pressures were predicted by the calculated HOFs and densities. Considered the detonation performance and thermal stability, three 3,3’-azobis-1,2,4,5-tetrazine, four TTZ derivatives, three C,C’-azobis-triazole derivatives, five N,N’-azobis-triazole derivatives, seven ATT derivatives, and six nitrogen-bridged polyheterocyclic compounds may be regarded as the potential candidates of HEDC. It is expected that our results can provide useful information for the molecular design of novel HEDC.In a word, the structures and properties of different types of a series of high-nitrogen energetic compounds were systematically studied by theroretical methods in this thesis. The structure-performance relationships were summarized. The potential candidates of HEDC were selected. The abundance of information provided here are helpful for the molecular design of HEDCs and performance predictions.