DFT Studies On Nitrogen-rich Pyrazino [2,3-e] [1,2,3,4] Tetrazine-based High-energy Density Compounds

High energy density compounds(HEDCs)store the chemical energy that releases upon external stimuli.HEDCs have numerous applications in civil and military fields such as buildings bulldozing,gas-producing agents,mining,fireworks,propellants,and high explosives etc.In the recent years,energetic nitrogen-rich compounds have attracted the researchers'attention due to their excellent detonation performance,suitable thermal stability,low sensitivity and large heat of formation(HOF).A computational investigation on the structure-property relations is very important to screen the new candidates of HEDCs.In this thesis,density functional theory(DFT)was employed to investigate the geometrical structures,HOFs,electronic structures,densities,detonation properties,thermal stability,and impact sensitivity of different series of energetic compounds based on the skeleton of pyrazino[2,3-e][1,2,3,4]tetrazine.According to the criteria of high energy and thermal stability,the promising potential HEDCs were selected.The content of the thesis has been divided into three parts.In the first part,we reported systematic investigations on the HOFs,electronic structures,detonation properties,thermal stability,and impact sensitivity of a series of pyrazino[2,3-e][1,2,3,4]tetrazine derivatives with different number of N-oxides.The HOFs were calculated by isodesmic reactions where all kinds of bonds both on the reactant and product sides were kept unchanged.The heat of detonations(Q)was calculated by the differences of the HOFs between products and energetic compounds.Their detonation pressures and detonation velocities were predicted by the calculated density(?)and Q values.Then the thermal stabilities of the designed compounds were assessed based on the calculated values of bond dissociation energies(BDEs).In order to estimate their impact sensitivity,the free spaces(?V)and impact sensitivities(h₅₀)were calculated.Based on high detonation properties,suitable thermal stabilities,and low sensitivity,4 compounds were finally selected as potential HEDCs.In the second part,the HOFs,electronic structures,densities,detonation properties,thermal stability,and impact sensitivity of a series of heterocycle-substituted derivatives of pyrazino[2,3-e][1,2,3,4]-1,3-di-N-oxide were investigated systematically by DFT.Their HOFs were predicted via isodesmic reactions.Their Q values were estimated by the HOF differences between products and the energetic compounds.The detonation velocities and detonation pressures were calculated by the Q and?values.The thermal stabilities were evaluated based on the BDEs.Finally,?V and h₅₀ were calculated to evaluate their impact sensitivities.By taking into account the detonation properties,thermal stabilities,and other properties,9compounds were selected as potential HEDCs,having huge potential to be synthesized experimentally.In the third part,we introduced the–CH₂(NO₂),–CH(NO₂)₂,–CF(NO₂),–CH₂(NF₂),–CH(NF₂)₂,and–CF(NF₂)substituents to 2,3-dihydro pyrazino[2,3-e][1,2,3,4]tetrazine molecule.The results show that the substitution of–CH(NO₂)₂ and–CH(NF₂)₂ are very effective to increase the HOFs.The derivatives with the–CH₂(NF₂)substituent have the largest HOMO and LUMO energy levels,while the CF(NO₂)₂-substituted derivatives have the lowest ones.The introduction of the–CF(NO₂)₂ and–CF(NF₂)₂ groups extremely increases the detonation properties.The analysis of the BDE values indicates that the N₂-R bond may be a trigger bond among all the bonds.The substitution of the–CH₂(NO₂)and–CH₂(NF₂)substituents decreases the impact sensitivity of the substituted derivatives.Compared with RDX and HMX,majority of the designed compounds have acceptable h₅₀ values.By taking into account all the properties,10 compounds(A2,A3,A6,B3,B6,C6,D3,D6,E3,and E6)were screened as the potential HEDCs.In short,the structures and different kinds of properties of a series of nitrogen-rich compounds based on the skeleton of pyrazino[2,3-e][1,2,3,4]tetrazine were studied systematically by the theoretical methods.The promising potential candidates were obtained.The knowledge presented in this thesis is helpful for designing new HEDCs and also for the experimental researchers in this field.