Theoretical studies on four-membered ring compounds with NF2, ONO2, N3, and NO2 groups

Density functional theory (DFT) method has been employed to study the geometric and electronic structures of a series of four-membered ring compounds at the B3LYP/6-311G** and the B3P86/6-311G** levels. In the isodesmic reactions designed for the computation of heats of formation (HOFs), 3,3-dimethyl-oxetane, azetidine, and cyclobutane were chosen as reference compounds. The HOFs for N(3) substituted derivations are larger than those of oxetane compounds with --ONO2 and/or --NF2 substituent groups. The HOFs for oxetane with --ONO2 and/or --NF2 substituent groups are negative, while the HOFs for N3 substituted derivations are positive. For azetidine compounds, the substituent groups within the azetidine ring affect the HOFs, which increase as the difluoroamino group being replaced by the nitro group. The magnitudes of intramolecular group interactions were predicted through the disproportionation energies. The strain energy (SE) for the title compounds has been calculated using homodesmotic reactions. For azetidine compounds, the NF2 group connecting N atom in the ring decrease the SE of title compounds. Thermal stability were evaluated via bond dissociation energies (BDE) at the UB3LYP/6-311G** level. For the oxetane compounds, the O--NO2 bond is easier to break than that of the ring C--C bond. For the azetidine and cyclobutane compounds, the homolyses of C--NX2 and/or N--NX2 (X = O, F) bonds are primary step for bond dissociation. Detonation properties of the title compounds were evaluated by using the Kamlet-Jacobs equation based on the calculated densities and HOFs. It is found that 1,1-dinitro-3,3-bis(difluoroamino)-cyclobutane, with predicted density of ca. 1.9 g/cm(3), detonation velocity (D) over 9 km/s, and detonation pressure (P) of 41 GPa that are lager than those of TNAZ, is expected to be a novel candidate of high energy density materials (HEDMs). The detonation data of nitro-BDFAA and TNCB are also close to the requirements for HEDMs.     

Substituent effect on the molecular stability, group interaction, detonation performance, and thermolysis mechanism of nitroamino-substituted cyclopentanes and cyclohexanes

Density functional theory (DFT) method has been employed to study the effect of nitroamino group as a substituent in cyclopentane and cyclohexane, which usually construct the polycyclic or caged nitra-mines. Molecular structures were investigated at the B3LYP/6-31G** level, and isodesmic reactions were designed for calculating the group interactions. The results show that the group interactions ac-cord with the group additivity, increasing with the increasing number of nitroamino groups. The dis-tance between substituents influences the interactions. Detonation performances were evaluated by the Kamlet-Jacobs equations based on the predicted densities and heats of formation, while thermal stability and pyrolysis mechanism were studied by the computations of bond dissociation energy (BDE). It is found that the contributions of nitroamino groups to the detonation heat, detonation velocity, detonation pressure, and stability all deviate from the group additivity. Only 3a, 3b, and 9a-9c may be novel potential candidates of high energy density materials (HEDMs) according to the quantitative cri-teria of HEDM (ρ≈ 1.9 g/cm3, D ≈ 9.0 km/s, P ≈ 40.0 GPa). Stability decreases with the increasing number of N-NO2 groups, and homolysis of N-NO2 bond is the initial step in the thermolysis of the title com-pounds. Coupled with the demand of thermal stability (BDE > 20 kcal/mol), only 1,2,4-trinitrotriazacy-clohexane and 1,2,4,5-tetranitrotetraazacyclohexane are suggested as feasible energetic materials. These results may provide basic information for the molecular design of HEDMs.     

Theoretical studies on the structures, densities, detonation properties and pyrolysis mechanism of energetic compounds containing pyridine ring

Density function theory has been employed to study a series of compounds containing pyridine ring at the B3LYP/6-31G* level. Detonation performance was evaluated by using the Kamlet–Jacobs equations based on the calculated densities and heats of formation. Some compounds have high densities (ca. 1.9 g cm⁻³) and good performance (detonation velocities over 9 km s⁻¹, detonation pressures about 39 GPa) and may be the potential candidates of high energy density materials. The thermal stability and the pyrolysis mechanism of the title compounds were investigated by the bond dissociation energies and the impact sensitivity predicted. Solvent effect has been investigated and it makes the title compounds more stable in solutions.     

A theoretical investigation on the structures,densities, detonation properties,and pyrolysis mechanism of the nitro derivatives of phenols

The nitro derivatives of phenols are optimized to obtain their molecular geometries and electronic structures at the DFT‐B3LYP/6‐31G* level. Detonation properties are evaluated using the modified Kamlet–Jacobs equations based on the calculated densities and heats of formation. It is found that there are good linear relationships between density, detonation velocity, detonation pressure, and the number of nitro and hydroxy groups. Thermal stability and pyrolysis mechanism of the title compounds are investigated by calculating the bond dissociation energies (BDEs) at the unrestricted B3LYP/6‐31G* level. The activation energies of H‐transfer reaction is smaller than the BDEs of all bonds and this illustrates that the pyrolysis of the title compounds may be started from breaking O? H bond followed by the isomerization reaction of H transfer. Moreover, the C? NO₂ bond with the smaller bond overlap population and the smaller BDE will also overlap may be before homolysis. According to the quantitative standard of energetics and stability as a high‐energy density compound, pentanitrophenol essentially satisfies this requirement. In addition, we have discussed the effect of the nitro and hydroxy groups on the static electronic structural parameters and the kinetic parameter. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Theoretical investigation on density,detonation properties,and pyrolysis mechanism of nitro derivatives of benzene and aminobenzenes

Nitro derivatives of benzene and aminobenzenes are optimized at the DFT‐B3LYP/6‐31G* level. The heat of formation (ΔH_f) and crystal theoretical density (ρ) are estimated to evaluate the detonation properties using the modified Kamlet–Jacobs equations. Thermal stability and the pyrolysis mechanism of the title compounds are investigated by calculating the bond dissociation energies (BDE) at the unrestricted B3LYP/6‐31G* level. The kinetic parameter and the static electronic structural parameters can be used to predict the stability and the relative magnitude of the impact sensitivity of homologues. According to the quantitative standard of the energy and the stability as an HEDC, the title compounds having more than four nitro groups satisfy this requirement. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Computational studies on tetrazole derivatives as potential high energy materials

The tetrazole is an important functionality of the most of energetic materials due to 80% nitrogen content, stability, and high enthalpy of formation. The present structure–property relationship study focuses on the optimized geometries of tetrazole derivatives obtained from density functional theory (DFT) calculations at B3LYP/6-31G* levels. The heat of formation (HOF) of tetrazole derivatives have been calculated by designing the appropriate isodesmic reactions. The increase in nitro groups on azole rings shows the remarkable increase in HOF. Density has been predicted by using CVFF force field. Increase in the nitro group increases the density. Detonation properties of the designed compounds were evaluated by using the Kamlet–Jacobs equation based on predicted densities and HOFs. Designed tetrazole derivatives show detonation velocity (D) over 8 km/s and detonation pressure (P) of about 32 GPa. Thermal stability was evaluated via bond dissociation energies (BDE) of the weakest C–NO₂ bond at B3LYP/6-31G* level. Charge on the nitro group has been used to assess the sensitivity correlation. Overall, the study implies that designed compounds of this series are found to be stable and expected to be the novel candidates of high energy materials (HEMs).     

Theoretical studies on the heats of formation, detonation properties, and pyrolysis mechanisms of energetic cyclic nitramines

Density functional theory calculations were performed to find comprehensive relationships between the structures and performance of a series of highly energetic cyclic nitramines. The isodesmic reaction method was employed to estimate the heat of formation. The detonation properties were evaluated by using the Kamlet-Jacobs equations based on the theoretical densities and HOFs. Results indicate the N-NO(2) group and aza N atom are effective substituents for enhancing the detonation performance. All cyclic nitramines except C11 and C21 exhibit better detonation performance than HMX. The decomposition mechanism and thermal stability of these cyclic nitramines were analyzed via the bond dissociation energies. For most of these nitramines, the homolysis of N-NO(2) is the initial step in the thermolysis, and the species with the bridged N-N bond are more sensitive than others. Considering the detonation performance and thermal stability, twelve derivatives may be the promising candidates of high energy density materials (HEDMs). The results of this study may provide basic information for the further study of this kind of compounds and molecular design of novel HEDMs.     

Theoretical studies on the structures, thermodynamic properties, detonation properties, and pyrolysis mechanisms of four trinitrate esters

Density function theory (DFT) has been employed to study the geometric and electronic structures of four trinitrate ester including nitroglycerin (NG), butanetriol trinitrate (BTTN), trimethanolethane trinitrate (TMETN) and trimethylolpropane trinitrate (TMPTN) at the B3LYP/6-31G^* level. Their IR spectra were obtained and assigned by vibrational analysis. Based on the frequencies scaled by 0.96 and the principle of statistic thermodynamics, the thermodynamic properties were evaluated, which were linearly related with the number of methylene groups as well as the temperature, obviously showing good group additivity. Detonation performances were evaluated by the Kamlet–Jacobs equations based on the calculated densities and heats of formation. It is found that density, detonation velocity, detonation pressure are decrease with the increase of the number methylene groups. Thermal stability and the pyrolysis mechanism of the title compounds were investigated by calculating the bond dissociation energies (BDE) at the B3LYP/6-31G^* level. For the nitrate esters, the ONO₂ bond is a trigger bond during thermolysis initiation process.     

Computational DFT studies on a series of toluene derivatives as potential high energy density compounds

Based on the full optimized molecular geometric structures at B3LYP/6-31G**, B3LYP/6-31+G**, B3P86/6-31G**, and B3P86/6-31+G** levels, the densities (ρ), detonation velocities (D), and pressures (P) for a series of toluene derivatives, as well as their thermal stabilities, were investigated to look for high energy density compounds (HEDCs). The heats of formation (HOFs) are also calculated via designed isodesmic reactions. The calculations on the bond dissociation energies (BDEs) indicate that the BDEs of the initial scission step are between 48 and 59 kcal/mol, and pentanitrotoluene is the most reactive compound, while 2,4,6-trinitrotoluene is the least reactive compound for toluene derivatives studied. A good linear relationship between BDE/E and impact sensitivity is also obtained. The condensed phase HOFs are calculated for the title compounds. These results would provide basic information for the further studies of HEDCs. The detonation data of pentanitrotoluene show that it meets the requirement for HEDCs.     

Theoretical Studies on the Structures,Thermodynamic Properties,Detonation Performance,and Pyrolysis Mechanisms for Six Dinitrate Esters

Density functional theory (DFT) has been employed to study the geometric and electronic structures of six dinitrate esters including ethylene glycol dinitrate (EGDN), diethylene glycol dinitrate (Di‐EGDN), triethylene glycol dinitrate (Tri‐EGDN), tetraethylene glycol dinitrate (Tetra‐EGDN), pentaethylene glycol dinitrate (Penta‐EGDN) and hexaethylene glycol dinitrate (Hexa‐EGDN) at the B3LYP/6‐31G* level. Their IR spectra were obtained and assigned by vibrational analysis. Based on the frequencies scaled by 0.96 and the principle of statistic thermodynamics, the thermodynamic properties were evaluated, which were linearly related with the number of CH₂CH₂O groups as well as the temperature, obviously showing good group additivity. Detonation performances were evaluated by the Kamlet‐Jacobs equations based on the calculated densities and heats of formation. It was found that density, detonation velocity, detonation pressure decreased with the increase of the number of CH₂CH₂O groups. Thermal stability and the pyrolysis mechanism of the title compounds were investigated by calculating the bond dissociation energies (BDE) at the B3LYP/6‐31G* level. For the nitrate esters, the O‐NO₂ bond is a trigger bond during a thermolysis initiation process.     

Computational characterization of 2, 4, 6, 8, 10, 12, 13-heptaazatetracyclo [5.5.1.03,11.05,9]tridecanes as potential energetic compounds

The characters of high density and high heat of formation of cage molecules have attracted a lot of investigations as potential energetic materials. Several such compounds have been synthesized, e.g., octanitrocubane, hexanitrohexaazaisowurzitane (CL-20), and 4-trinitroethyl-2, 6, 8, 10, 12-pentanitrohexaazaisowurtzitane(TNE-CL-20). In the present study, a new cage compound, namely 2, 4, 6, 8, 10, 12, 13-heptaazatetracyclo [5.5.1.0^3,11.0^5,9] tridecane (HATT), was proposed. Density functional theory has been employed to study the geometric and electronic structures for a series of nitro derivatives of HATT at the B3LYP/6-31G(d,p) level. Thermodynamic properties derived on the basis of statistical thermodynamic principles are linearly correlated with the numbers of nitro group as well as the temperature. Detonation performance was evaluated based on the calculated densities and heats of formation. It is found that some title compounds have high densities of ca. 1.9 g cm^?3, detonation velocities over 9.0 km s^?1, and detonation pressures of about 40.0 GPa and may be novel potential candidates of high energy density compounds (HEDCs). Thermal stability and pyrolysis mechanism of the nitro HATTs were investigated by calculating the bond dissociation energies (BDE). In conjunction with the detonation performance and thermal stability, HATTs with no less than five nitro groups are recommended as the preferred candidates of HEDCs. These results provide basic information for the further studies of cage compounds.     

Theoretical investigation on the structures,densities, and detonation properties of polynitrotetraazaoctahydroanthracenes

The polynitrotetraazaoctahydroanthracenes were optimized to obtain their molecular geometries and electronic structures at density functional theory–B3LYP/6‐31+G(d) level. Detonation velocities (D) and detonation pressures (P) were estimated for this nitramine compounds using Kamlet‐Jacobs equations, based on the theoretical densities (ρ) and heats of formation. It is found that there are good linear relationships between volume, density, detonation velocity, detonation pressure and the number of nitro group. Thermal stability of the compounds was investigated by calculating the bond dissociation energies and energy gap (ΔE_LUMO–HOMO). The simulation results reveal that molecule H performs similarly to famous explosive RDX. These results provide basic information for molecular design of novel high energetic density compounds. © 2011 Wiley Periodicals, Inc.     

Theoretical studies on polynitrobicyclo[1.1.1]pentanes in search of novel high energy density materials

Bicyclo[1.1.1]pentane is a highly strained hydrocarbon system due to close proximity of nonbonded bridge head carbons. Based on fully optimized molecular geometries at the density functional theory using the B3LYP/6-31G* level, densities, detonation velocities, and pressures for a series of polynitrobicyclo[1.1.1]pentanes, as well as their thermal stabilities were investigated in search for high energy density materials (HEDMs). The designed compounds with more than two nitro groups are characterized by high heat of formation and magnitude correlative with the number and space distance of nitro groups. Density was calculated using the crystal packing calculations and an increase in the number of nitro groups increases the density. The increase in density shows a linear increase in the detonation characteristics. Bond dissociation energy was analyzed to determine thermal stability. Calculations of the bond length and bond dissociation energies of the C-NO₂ bond indicate that this may be the possible trigger bond in the pyrolysis mechanism. 1,2,3-Trinitrobicyclo[1.1.1]pentane (S3), 1,2,3,4-tetranitrobicyclo[1.1.1]pentane (S4), and 1,2,3,4,5-pentanitrobicyclo[1.1.1]pentane (S5) have better energetic characteristics with better stability and insensitivity, and as such may be explored in defense applications as promising candidates of the HEDMs series.     

反式-1,4,5,8-四硝基-1,4,5,8-四氮杂萘烷异构体热解机理与稳定性的理论研究

运用密度泛函理论和半经验分子轨道方法,对一系列高能杂环硝胺—反式-1,4,5,8-四硝基-1,4,5,8-四氮杂萘烷异构体的热解机理和稳定性进行了系统地计算研究。在B3LYP/6-31G**和PM3水平上,分别计算了标题物的化学键离解能(BDE)和热解反应活化能(Ea),并根据BDE和Ea数值考察了硝胺取代基对化合物稳定性和热解机理的影响;同时,还详细考察了BDE与Ea、化学键重叠布居数、前线轨道能级以及能隙之间的相关性。结果表明,由BDE、Ea和静态电子结构参数推断的标题物热稳定性和热解机理的结论基本是一致的,N-NO2键均裂是标题物的热解引发步骤,间位取代异构体较对位取代异构体稳定,而邻位取代的异构体稳定性最差。     

Computational studies on polynitrohexaazaadmantanes as potential high energy density materials

Polynitrohexaazaadamantanes (PNHAAs) have been the subject of much recent research because of their potential as high energy density materials (HEDMs). The B3LYP/6-31G method was employed to evaluate the heats of formation (HOFs) for PNHAAs by designing isodesmic reactions. The HOFs are found to be correlative with the number (n) and the space orientations of nitro groups. Detonation velocities (D) and detonation pressures (P) were estimated for PNHAAs by using the well-known Kamlet-Jacobs equations, based on the theoretical densities (rho) and HOFs. It is found that D and P increase as n ranges from 1 to 6, and PNHAAs with 4-6 nitro groups meet the criteria of an HEDM. When n is over 6, rho of PNHAAs slightly increases; however, the chemical energy of detonation (Q) decreases so greatly that both D and P decrease. The calculations on bond dissociation energies suggest that the N-N bond be the trigger bond during the pyrolysis initiation process of each PNHAA, and with increasing n, N-N bond dissociation energy (E(N-N)) decreases on the whole, that is to say, the relative stability of PNHAAs decreases. All E(N-N)(s) of PNHAAs are more than 30 kcal.mol(-1), which further proves that four PNHAAs with 4-6 nitro groups can be used as the candidates of HEDMs. Considering the synthesis difficulty and the performance as an energetic compound, we finally recommended 2,4,6,8,10-pentanitrohexaazaadamantane as the target HEDM for PNHAAs.     

Theoretical studies on high energetic density nitramine explosives containing pyridine

The insensitive property of explosives containing pyridine is combined with the high energy of nitramine explosives,and the concept of new nitramine explosives containing pyridine is proposed,into which nitramine group with N N bonds is introduced as much as possible.Based on molecular structures of nitramine compounds containing pyridine,density functional theory(DFT) calculation method was applied to study designed molecules at B3LYP/6-31+G(d) level.The geometric and electronic structures,density,heats of formation(HOF),detonation performance and bond dissociation energies(BDE) were investigated and comparable to 1,3,5-trinitro-1,3,5-triazinane(RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane(HMX).The simulation results reveal that molecules B and D perform similarly to traditionally used RDX.Molecule E outperform RDX,with performance that approach that of HMX and may be considered as potential candidate of high energy density compound(HEDC).These results provide basic information for molecular design of novel high energetic density compounds.     

Substituent effects on heats of formation, group interactions, and detonation properties of polyazidocubanes

We have calculated the heats of formation (HOFs) for a series of polyazidocubanes by using the density functional theory (DFT), Hartree-Fock, and MP2 methods with 6-31G* basis set as well as semiempirical methods. The cubane skeleton was chosen for a reference compound, that is, the cubane skeleton was not broken in the process of designing isodesmic reactions. There exists group additivity for the HOF with respect to the azido group. The semiempirical AM1 method also produced reliable results for the HOFs of the title compounds, but the semiempirical MINDO3 did not. The relationship between HOFs and molecular structures was discussed. It was found that the HOF increases 330-360 kJ/mol for each additional number of the azido group being added to the cubane skeleton. The distance between azido groups slightly influences the values of HOFs. The interacting energies of neighbor azido groups in polyazidocubanes are in the range of 2.3 approximately 6.6 kJ/mol, which are so small and less related to the substituent numbers. The average interaction energy between nearest neighbor --N3 groups in the most stable conformer of octaazidocubane is 2.29 kJ/mol at the B3LYP/6-31G* level. The relative stability related to the number of azido groups of the title compounds was assessed based on the calculated HOFs, the energy gaps between the frontier orbitals, and the bond orders of the C--N3 and C--C bonds. The predicted detonation velocity of hepta- and octa-derivatives is over 9 km/s, and the detonation pressure of them is ca. 40 GPa or over.     

Looking for high energy density compounds applicable for propellant among the derivatives of DPO with -N3, -ONO2, and -NNO2 groups

The derivatives of DPO (2,5-dipicryl-1,3,4-oxadiazole) are optimized to obtain their molecular geometries and electronic structures at the DFT-B3LYP/6-31G* level. The bond length is focused to primarily predict thermal stability and the pyrolysis mechanism of the title compounds. Detonation properties are evaluated using the modified Kamlet-Jacobs equations based on the calculated densities and heats of formation. It is found that there are good linear relationships between density, detonation velocity, detonation pressure, and the number of azido, nitrate, and nitramine groups. According to the largest exothermic principle, the relative specific impulse is investigated by calculating the enthalpy of combustion (ΔH(comb)) and the total heat capacity (C(p,gases)). It is found that the introduction of -N(3), -ONO(2), and -NNO(2) groups could increase the specific impulses and II-4, II-5, and III-5 are potential candidates for High Energy Density Materials (HEDMs). The effect of the azido, nitrate, and nitramine groups on the structure and the properties is discussed.     

Theoretical investigations on the structure, density, thermodynamic and performance properties of amino-, methyl-, and nitroimidazoles and their N-oxides

Density functional theory calculations at the B3LYP/aug-cc-pVDZ level have been performed to explore the structure, stability, heat of explosion, density, and the performance properties of amino-, methyl-, and nitroimidazoles. N-Nitroimidazoles have shown lower densities compared with those of C-nitroimidazoles. Detonation properties of title compounds were evaluated by using Kamlet–Jacob semi-empirical equations based on the predicted densities and the calculated heats of detonation. It has been found that some compounds with the calculated densities 2.0 g/cm³, detonation velocities over 9.10 km/s and detonation pressures of about 45 GPa (some even over 50 GPa) may be novel potential high energy materials. The higher performance of nitroimidazole-N-oxides is apparently due to their higher densities (2.0–2.515 g/cm³). Heat of explosion, stability, density, and performance properties are related to the number and relative positions of –NO₂, –NH₂, and –CH₃ groups of the imidazole ring. The designed nitroimidazoles satisfy the criteria of high energy materials.     

Theoretical Study on Nitroso-Substituted Derivatives of Azetidine as Potential High Energy Density Compounds

At the B3 PW91/6-311+G(d,p)//MP2/6-311+G(d,p) level, molecular densities, detonation velocities, and detonation pressures of nitroso substituted derivatives of azetidine with their thermal stabilities were investigated to look for high energy density compounds(HEDCs). It was found that the azetidine derivatives had high heat of formation(HOF) and large bond dissociation energy(BDE). Intramolecular hydrogen bonds were located in three molecules(1, 4, and 5), and the molecular stability were improved markedly as well. For 5 and 6, the detonation performances(D= 9.36 km/s and 10.80 km/s, P= 44.42 GPa and 60.70 GPa, respectively) meet requirements as high energy density compounds. This work may provide basic information for further study of title compounds.