Theoretical Studies On Molecular Design And Performance Of Energetic Nitrogen-rich Heterocyclic Compounds

In the thesis,different types of energetic nitrogen-rich heterocyclic compounds including bridged nitrogen-rich heterocyclic,polycyclic,monocyclic and bicyclic nitramine,and cage nitramine compounds were designed by employing some different design strategies such as incorporating intermolecular bridging groups,intramolecular linking groups,fusing with aromatic heterocycles and different substituents.Then,their molecular structures,heats of formation(HOFs),energetic properties,strain energies,thermal stability,impact sensitivity,and crystal structures were studied using quantum chemistry and performance computational methods.Finally,some novel candidates of high energy density compounds(HEDCs)with excellent performance and low sensitivity were screened.The main research contents include the following aspects:(1)A series of bridged di-1,3,5-triazine derivatives with different linkages(-,-CH₂-,-CH₂-CH₂-,-CH=CH-,-NH-,-NH-NH-,or-N=N-)and different substituents(-NH₂,-NO₂,-ONO₂,-NF₂,or-N₃)were designed.The results indicate that introducing the-N=N-,-NF₂,or-ONO₂group is very useful for enhancing the detonation performance of these derivatives.Five bridged di-1,3,5-triazine derivatives were selected as the potential candidates of HEDCs with higher performance and less sensitivity.A series of furazano[3,4-b]pyrazine derivatives with different substituents(-NO₂,-ONO₂,-NF₂,or-N₃),nitrogen-containing heterocyclic rings(furazan,tetrazine,tetrazole,or triazole ring),and NO₂-substituted heterocycles were designed.The results show that incorporating the nitrogen-containing heterocycles into the parent ring is not favorable for increasing its detonation properties.However,further connecting-NO₂ with the heterocycles is useful for increasing their densities and detonation properties.Six furazano[3,4-b]pyrazine derivatives can be considered as the potential candidates of HEDCs.(2)A series of trinitromethyl-or dinitromethyl-modified derivatives of1,3,5-triazacyclohexane,1,3,5,7-tetraazacyclooctane,and 2,4,6,8,10,12-hexaazaisowurtzitane were designed.It shows that the-C(NO₂)₃ group is an effective structural unit for increasing the detonation properties of the title compounds.However,when the molecule contains three or more-C(NO₂)₃groups,its detonation velocity and pressure decrease.In addition,the substitution of the-CH(NO₂)₂ or-C(NO₂)₃ group increases the impact sensitivities of the derivatives.20 energetic compounds were regarded as the potential candidates of HEDCs with remarkable energetic properties,good thermal stability,and moderate sensitivity.(3)A series of substituted difurazano[3,4-b:3',4'-e]piperazines and their analogues were designed by 1,4-dinitrofurazano[3,4-b]piperazine skeleton fused with a furazan ring,tetrazole ring,triazole ring,or tetrazine ring.All the substituted derivatives present prominent energetic properties.Most of the substituted derivatives have comparable?,D and P with HMX.The calculated detonation properties reveal that incorporating a five-or six-membered aromatic heterocycle to construct a fused ring system greatly enhances their detonation properties.Eight compounds were selected as the potential candidates of HEDCs.(4)10 novel azaoxaisowurtzitane cage compounds and 6 azaoxaadamantane cage compounds were designed by introducing the oxygen atoms into the azaisowurtzitane and hexaazaoxaadmantane cage to replace the N-NO₂ groups,respectively.Although the introduction of the oxygen atom in the cage is not helpful for increasing their HOFs and densities,all the azaoxaisowurtzitane and azaoxaadamantane cage compounds exhibit high density and outstanding detonation properties.Moreover,the introduction of the oxygen atom can improve thermal stability and effectively decrease the sensitivity for these cage compounds.12 novel cage compounds are highly recommended as the potential HEDCs.Therefore,it can be concluded that constructing the azaoxaisowurtzitane or azaoxaadamantane cage by introducing oxygen atom(s)is an effective way to obtain novel HEDCs with excellent detonation properties and low sensitivity.(5)Four bicyclic nitramines were designed by incorporating-N(NO₂)-CH₂-N(NO₂)-,-N(NO₂)-,and-O-linkages into the 1,3,5,7-tetrazacyclooctane framework.Compared to the parent compound HMX,all the title compounds have much higher density,better detonation properties,and better oxygen balance.The results indicate that the design strategy that constructing bicyclic nitramines based on the HMX framework by incorporating the intramolecular linkages is very useful for developing novel energetic compounds with excellent detonation performance and low sensitivity.All of the four bicyclic nitramines are promising candidates for HEDCs.(6)A series of cage nitramine compounds with novel cage skeletons were designed based on the bicyclic nitramines framework.It is found that seven novel cage compounds have higher detonation properties and better oxygen balance than the parent compound bicyclic nitramine.Thus,they are promising candidates for HEDCs.Especially,2,4,6,8,9-pentanitro-2,4,6,8,9-pentaazatricyclo[3.3.1.0^3,7]nonane(PATN),a novel cage nitramine,may be regarded as a very attractive potential HEDC.Compared to hexanitrohexaazaadamantane(HNHAA),PATN possesses a relatively simple structure with only five nitramine moieties and exhibits better detonation properties,better thermal stability,and lower impact sensitivity than that of HNHAA.