Theoretical Study On The Structure And Performance Of High Energetic Compounds

The dissertation is devoted to systematic researches on the structures and properties of several series of energetic compounds and well-known high energy density compounds(HEDC),using modern theoretical and computational chemistry methods,such as quantum mechanics(QM)and molecular mechanics(MM).The whole work can be divided into three parts:The first part concentrates on the theoretical studies on the structures and properties of series of arenes,and at the same time considers the "molecular design" of HEDC.The fully optimized structures,assigned infrared(IR)spectra,and thermodynamic properties(C_p,m⁰,S_m⁰ and H_m⁰)related with the number of nitro and amino groups as well as the temperature in 200～800 K of two types of nitro derivatives of benzene and aminobenzenes are obtained at the DFT-B3LYP/6-31G^* level.According to the volume inside a contour of 0.001e/Bohr³,the molecular theoretical density(ρ)is evaluated,and detonation velocity(D)and detonation pressure(P)are estimated according to the Kamlet-Jacobs equation.The UHF-PM3 method is employed to evaluate thermolysis activation energies(E_a).Bond dissociation energies(BDEs)of three possible trigger bonds in their thermolysis are computed by the B3LYP/6-31G^* method under the unrestricted model,and their pyrolysis mechanisms are ascertained to be the homolysis of C-NO₂ bond.It is found that,the static electronic structural parameters(the Mulliken bond population M_C-NO2 and the net charge of the nitro group Q_-NO2)and the kinetic parameters(BDE and E_a) are related with each other,which indicates that they all can parallelly or equivalently be used to identify the stability and the relative magnitude impact sensitivity for homologous energetic materials.Based on the QM calculations,the quantitative criteria of detonation performance as HEDCs(ρ≈1.9 g/cm³,D≈9.0 km/s,and P≈40.0 GPa)and the stability requirement(BDE of the initial step in thermolysis BDE≈80～120 kJ/mol) are employed to recommend several potential HEDC objectives from the title compounds.Pentanitrobenzene,hexanitrobenzene and pentanitroaniline agree with the forementioned criteria of HEDCs. The nitro derivatives of phenols and methylbenzenes have been studied similarly at the DFT-B3LYP/6-31G^* level.The fully optimized structures,IR,thermodynamic properties(C_p,m⁰,S_m⁰ and H_m⁰),theoretical molecular densityρ,detonation velocity D, detonation pressure P and BDEs of the possible trigger bonds in their thermolysis are obtained.Comparing the kinetic result,it is found that,for the nitro derivatives of phenols,their pyrolysis initiation is the isomerization reactions of the O-H bond,i.e., breaking of O-H bond followed by the isomerization reactions of the H transferring is prior to the homolysis of C-NO₂ bond,and for the nitro derivatives of methylbenzenes, their pyrolysis mechanism is the breaking of C-H bond followed by the H transferring. According to the quantitative criteria of HEDCs and stability demand, 2,3,4,5,6-pentanitrobenzenephenol and 2,3,4,5,6-pentanitrotoluene are potential candidates.The second part focuses on the theoretical studies on the structures and properties for the typical detonation-transferring explosives,such as the derivatives HNS(2,2',4,4',6,6'-hexanitrostilbene)and 2,5-dipicryl-1,3,4-oxadiazole(DPO).For the derivatives of HNS substituted for nitro,amino and hydroxy groups,the fully optimized structures,assigned IR spectra,and thermodynamic properties(C_p,m⁰, S_m⁰ and H_m⁰)related with the various groups and the temperature in 200～800 K are obtained at the DFT-B3LYP/6-31G^* level.Theoretical densityρ,detonation velocity D,and detonation pressure P of each compound are predicted.BDEs of seven possible trigger bonds in their thermolysis are computed by the(U)B3LYP/6-31G^* method.Refering to the bond overlap populations,the homolysis is initiated from breaking the trigger linkage C-NO₂ bond for the nitro and amino derivatives of HNS, while for hydroxy derivatives it is started from breaking O-H bond followed by the isomerization reactions of the H transferring.Considering the energetic characteristic and the thermal stability,2,2',3,3',4,4',5,6,6'-nonanitrostilbene and 2,2',3,3', 4,4',5,5',6,6'-decanitrostilbene essentially satisfy the quantitative criteria of HEDCs. The energy and density of HNS are improved when it is substituted by -NO₂ group. However,the substitution of -NH₂ group increases the insensitivity and stability of HNS.The fully optimized structures(C₂),assigned IR spectra,and thermodynamic properties(C_p,m⁰,S_m⁰ and H_m⁰)related with the temperature in 200～800 K are obtained similarly at the DFT-B3LYP/6-31G^* level.Theoretical densityρ, detonation velocity D,and detonation pressure P are predicted.BDEs of four possible trigger bonds in their thermolysis are computed by the(U)B3LYP/6-31G^* method.The pyrolysis mechanism is found to be the homolysis of C-NO₂,N-N or C-O bond.It is presumed thatρ,D and P are probably improved so as to become HEDC when DPO is substituted by -NO₂ group.MM method is used to search for the most possible packing of DPO among the seven most possible space groups(P2₁/c,P-1,P2₁2₁2₁,P2₁,C2/c,Pbca and Pna2₁) with Dreiding and Compass force field,the reasonable crystal structures are predicted to pack in P2₁2₁2₁ space group.Periodic ab initio calculations are performed on the predicted crystal structure using the DFT-GGA-PBE method,and the density of states (DOS),the partial density of states(PDOS)and the band gap(â–³Eg)are obtained, which indicates that the N-N,C-O or C-NO₂ bonds are possible trigger bonds and DPO is suitable to be used as a detonation-transferring explosive.The third part centers on establishing QSAR on sensitivity using linear regression method.The 57 nitramines and nitro arenes have been studied at the DFT-B3LYP/6-31G^* level.The fully optimized structures,theoretical densityρ,detonation velocity D,and detonation pressure P of each compound are predicted.It is found that,there are qualitative or quantitative relationships between the detonation velocity,pressure and electric sensitivity(E_ES).For the compounds with metylenenitramine units(-CH₂N(NO₂)-)in their molecules(such as ORDX,AcAn and HMX)or with the better symmetrical cyclic nitramines but without metylenenitramine units(such as DNDC and TNAD),there is a linear relationship between the square of detonation velocity(D²)and electric spark sensitivity E_ES,and the equation are E_ES=-0.492 D²+42.68(R=0.957)and E_ES =-62.97011gP+100.903(R=0.955).For nitro arenes,this series of compounds are classified and discussed and there are linear relationships between D² or P and E_ES.For the first type of compounds mainly belonging to C,H,N,O type explosives,whose N and O atoms are in the form of -NO₂ group,and including the aromatic sulfides,the formula are E_ES=-0.246 D²+20.465(R=0.861)and E_ES=-0.489P+18.891(R=0.866);For the compounds with -CH₃ or -CH₂CH₂- groups whose ortho position have -NO₂ group,their linear relationships are E_ES=-0.984D²+60.101(R=0.998)and E_ES=-1.748P+48.103 (R=0.998);For the compounds with -NH₂,-OH,-N=N- and -NH- groups in the molecules,their linear relationships are E_ES=-0.520D²+41.488(R=0.963)and E_ES =-0.925P+35.170(R=0.966).Therefore,the more easily calculated detonation characteristics(D and P)can be used to theoretically predict or judge the magnitude of E_ESwhich is difficult to mensurate.In a word,the systemic theroretical studies on the structures and properties and the molecular design have been investigated for the energetic compounds,which explain a great deal of the experimental fact and predict many unknown results.The abundance of information and the rules provided are used to instruct the experimental synthesize,which not only decrease the waste that may be resulted from experiment, but also shorten the period of experiment and increase safety.The work of thesis has successfully completed the various tasks assigned by the projects of National 973 and National Nature Science Foundation of China.