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).     

Density function theory study on energetic nitro-triaziridine derivatives

The series of nitro-triaziridines had been studied as high-energy density compounds at B3LYP/6-311G** and MP2/6-311G** levels by means of density functional theory. The heats of formation (HOFs), bond dissociation energies, and detonation performance had been calculated in detail. It was found that all nitro-triaziridines have high position HOFs, and electron-withdrawing of nitro, the steric hindrance, and abundant N–N bond had positive effect with increasing values of HOFs. The thermodynamic stability is estimated by bond dissociation energy and available free space per molecule in unit cell. The detonation performance had been estimated via Kamlet–Jacobs equation and relative specific, However, two different consequences were obtained for detonation performance. Hence, for nitro-triaziridines derivatives, we assumed that a large number of extra oxygen was produced in combustion reaction or explosive reaction, which was negative for the energy released. Therefore, the oxygen balance must be considered for designing high-energy compounds. We also assumed that the Kamlet–Jacobs equation may not be applicable for the compounds, which was constituted of only oxygen, hydrogen, and nitrogen elements.     

Molecular design of trinitromethyl-substituted nitrogen-rich heterocycle derivatives with good oxygen balance as high-energy density compounds

Density functional theory method was used to study the heats of formation (HOFs), electronic structure, energetic properties, and pyrolysis mechanism of a series of trinitromethyl-substituted heterocycle (including triazole, tetrazole, furazan, tetrazine, and fused heterocycles) derivatives. It is found that the fused ring, tetrazine, and tetrazole are effective structural units for increasing the HOFs of the derivatives. The substitution of the combination of nitro and trinitromethyl is very useful for improving their HOFs. The calculated energetic properties indicate that the combination of the nitro and trinitromethyl is very helpful for improving their detonation properties and oxygen balances (OB). Most of the title compounds have a good OB over zero. The OB of six compounds are very high and over 22. An analysis of the bond dissociation energies for several relatively weak bonds suggests that the N–O bond in the ring is a trigger bond for BIII-1, CI-3, and CI-4, and the ring–NO₂ and (NO₂)₂C–NO₂ bond cleavage is likely to happen in thermal decomposition for the remaining compounds. Considering the detonation performance and thermal stability, seven compounds could be regarded as potential candidates for high-energy compounds. Four compounds may be used as the novel high-energy oxidizers.     

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.     

高能量密度材料3,3′-偶氮-1,2,4,5-四嗪衍生物的分子设计

运用密度泛函理论(DFT)方法,计算系列3,3′-偶氮-1,2,4,5-四嗪衍生物的生成热.结果显示:—N3取代基在增加3,3′-偶氮-1,2,4,5-四嗪衍生物的生成热方面起了非常重要的作用.通过分析标题化合物的最弱键离解能发现:—NH2或—N3取代基非常有利于增加衍生物的热稳定性.计算的爆速(D)和爆压(p)数值表明:—NO2或—NF2取代基有利于提高3,3′-偶氮-1,2,4,5-四嗪衍生物的爆轰性能.综合爆轰性能和热稳定性的计算结果,3种3,3′-偶氮-1,2,4,5-四嗪衍生物可以作为潜在的品优高能量密度材料(HEDM)候选物.     

Theoretical studies of furoxan-based energetic nitrogen-rich compounds

Density functional theory calculations were performed to study the effects of different substituents and nitrogen-containing heterocyclic rings on the heats of formation (HOFs), energetic properties, and thermal stability for a series of furoxan derivatives. The isodesmic reaction method was employed to calculate the HOFs of the derivatives using total energies obtained from electronic structure calculations. The detonation velocities and pressures were evaluated by using the semiempirical Kamlet–Jacobs equations, based on the theoretical densities and HOFs. The bond dissociation energies and bond orders for the weakest bonds were analyzed to investigate the thermal stability of the furoxan derivatives. These results provide basic information for the molecular design of novel high energy density materials.     

Density functional calculation on a high energy density compound having the formula C2OH4?n (NO2) n

A series of ethylene oxide derivations, C₂OH_4?Cn (NO2) _n (x?=?1?C4), has been designed computationally. We calculated the heats of formation (HOFs), bond dissociation energy (BDE), and explosive performances (detonation velocity and detonation pressure) of the title compounds by using density functional theory with 6-311G** basis set. The results show that most of ethylene oxide derivations have positive HOFs values except I. All the calculated BDE and the bond dissociation energies without zero-point energy corrections (BDE⁰) are larger than 200?kJ?mol^?1, which indicate that all the ethylene oxide derivations have good thermal stabilities. The explosive performances of most of ethylene oxide derivations would rank up with cyclotrimethylenetrinitramine (RDX). The results have not only shown that these compounds may be used as high energy density compounds, but also provide some useful information for further syntheses.     

Theoretical studies on heats of formation,detonation properties,and bond dissociation energies of monofurazan derivatives

The heats of formation (HOFs) for a series of monofurazan derivatives were calculated by using density functional theory. It is found that the ? CN or ? N₃ group plays a very important role in increasing the HOF values of the furazan derivatives. The detonation velocities and detonation pressures of the furazan derivatives are evaluated at two different levels. The results show that the ? NF₂ group is very helpful for enhancing the detonation performance for the furazan derivatives, but the case is quite the contrary for the ? CH₃ group. An analysis of the bond dissociation energies and bond orders for the weakest bonds indicate that the substitutions of ? CN group are favorable and enhances the thermal stability of the furazan derivatives, but the ? NO₂ groups produce opposite effects. These results provide basic information for the molecular design of novel high‐energy density materials. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Theoretical Studies on Energetic Property and Stability of Pyrazine and Pyridine Derivatives

Density functional calculations at the B3LYP level with 6‐311G** and aug‐cc‐pVDZ basis sets were performed to predict the heats of formation (HOFs) for two pyrazine derivatives and eight pyridine derivatives. In the isodesmic reactions designed for the computation of heats of formation (HOFs), pyrazine and pyridine were chosen as reference compounds. The N‐oxidations for the ring nitrogen of pyrazine and pyridine derivatives decrease the HOF values when N‐oxide oxygen is neighboring with amino groups, but increase when it neighbors with nitro groups. Thermal stability was evaluated via bond dissociation energies (BDE) at the UB3LYP/6‐311G** level. As a whole, the homolysis of C–NO₂ bonds is the main step for bond dissociation of the title compounds. The BDE values of title compounds are influenced by intramolecular hydrogen bonds. The hydrogen bond effects associated with the length of the H···O bonds were analyzed by the electron density at the critical points and natural bond orbital.     

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 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.     

Computational study of energetic nitrogen‐rich derivatives of 1,1′‐ and 5,5′‐bridged ditetrazoles

Density functional theory method was used to study the heats of formation (HOFs), electronic structure, energetic properties, and thermal stability for a series of bridged ditetrazole derivatives with different linkages and substituent groups. The results show that the ? N₃ group and azo bridge (? N?N? ) play a very important role in increasing the HOF values of the ditetrazole derivatives. The effects of the substituents on the HOMO–LUMO gap are combined with those of the bridge groups. The calculated detonation velocities and detonation pressures indicate that the ? NO₂, ? NF₂, ? N?N? , or ? N(O)?N? group is an effective structural unit for enhancing the detonation performance for the derivatives. An analysis of the bond dissociation energies for several relatively weak bonds suggests that the N? N bond in the ring or outside the ring is the weakest one and the N? N cleavage is possible to happen in thermal decomposition. Overall, the ? CH₂? CH₂? or ? NH? NH? group is an effective bridge for enhancing the thermal stability of the bridged ditetrazoles. Because of their desirable detonation performance and thermal stability, five compounds may be considered as the potential candidates of high‐energy density materials (HEDMs). These results provide basic information for the molecular design of novel HEDMs. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Theoretic design of 1,2,3,4-tetrazine-1,3-dioxide-based high-energy density compounds with oxygen balance close to zero

Density functional theory method was used to study the heats of formation (HOFs), electronic structure, energetic properties, and thermal stability for a series of 1,2,3,4-tetrazine-1,3-dioxide derivatives with different substituents and bridge groups. It is found that the groups –NO₂, –C(NO₂)₃, and –N=N– play a very important role in increasing the HOFs of the derivatives. The effects of the substituents on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and HOMO–LUMO gaps are coupled to those of different substituents and bridges. The calculated detonation velocities and pressures indicate that the group –NO₂, –NF₂, –ONO₂, –C(NO₂)₃, or –NH– is an effective structural unit for enhancing the detonation performance for the derivatives. An analysis of the bond dissociation energies for several relatively weak bonds indicates that incorporating the groups –NO₂, –NF₂, –ONO₂, –C(NO₂)₃, and –N=N– into parent ring decreases their thermal stability. Considering the detonation performance and thermal stability, 18 compounds may be considered as the target compounds holding the greatest potential for synthesis and use as high-energy density compounds. Among them, the oxygen balances of four compounds are equal to zero. These results provide basic information for the molecular design of the novel high-energy compounds.     

Theoretical studies on the structures, heats of formation, energetic properties and pyrolysis mechanisms of nitrogen-rich difurazano[3,4-b:3′,4′-e]piperazine derivatives and their analogues

The molecular structure, heats of formation, energetic properties, strain energy and thermal stability for a series of substituted difurazano[3,4-b:3′,4′-e]piperazines and their analogues were studied using density functional theory. The results show that it is a useful way to increase the heat of formation values of energetic compounds by incorporating a five- or six-membered aromatic heterocycle to construct a fused ring system. The calculated detonation properties reveal that introducing one heterocycle to construct a fused ring structure greatly enhances their detonation properties. The substitution of the –NF₂, –NO₂ or –NHNO₂ group is very useful for enhancing the detonation performance for the substituted derivatives. According to molecular structure and natural bond orbital analysis, the introduction of the –NO₂, –NF₂ or –NHNO₂ group decreases the stability of the substituted derivative. There is a weak N–NO₂ bond conjugation in the NO₂-substituted derivatives. An analysis of the bond dissociation energies for several relatively weak bonds suggests that all the unsubstituted derivatives have good thermal stability, but the substitution of –NO₂ or –NF₂ remarkably decreases their stability. Considering the detonation performance and thermal stability, eight compounds may be considered as the potential candidates of high-energy density materials with less sensitivity.     

Substituent effects on the properties related to detonation performance and sensitivity for 2,2',4,4',6,6'-hexanitroazobenzene derivatives

To look for superior and safe high energy density compounds (HEDCs), 2,2',4,4',6,6'-hexanitroazobenzene (HNAB) and its -NO(2), -NH(2), -CN, -NC, -ONO(2), -N(3), or -NF(2) derivatives were studied at the B3LYP/6-31G* level of density functional theory (DFT). The isodesmic reactions were applied to calculate the heats of formation (HOFs) for these compounds. The theoretical molecular density (ρ), detonation energy (E(d)), detonation pressure (P), and detonation velocity (D), estimated using the Kamlet-Jacobs equations, showed that the detonation properties of these compounds were excellent. The effects of substituent groups on HOF, ρ, E(d), P, and D were studied. The order of contribution of the substituent groups to P and D was -NF(2) > -ONO(2) > -NO(2) > -N(3) > -NH(2). Sensitivity was evaluated using the nitro group charges, frontier orbital energies, and bond dissociation enthalpies (BDEs). The trigger bonds in the pyrolysis process for all these HNAB derivatives may be Ring-NO(2), Ring-N═N, Ring-NF(2), or O-NO(2) varying with the attachment of different substituents. BDEs of trigger bonds except those of -ONO(2) derivatives are relatively large, which means these compounds suffice the stability request of explosives. Taking both detonation properties and sensitivities into consideration, some -NF(2) and -NO(2) derivatives may be potential candidates for HEDCs.     

Theoretical studies of 1,2,4,5-tetrazine-based energetic nitrogen-rich compounds

Density functional theory calculations were performed to find the relationships between the structures and performance of a series of 1,2,4,5-tetrazine-based energetic derivatives. The isodesmic reaction method was employed to estimate the heats of formation (HOFs). The result shows that the azo or azoxy group is one of the most energetic functional groups known and its substitution can drastically increase HOFs of a molecule. The detonation properties were also evaluated by the Kamlet–Jacobs equations based on the theoretical densities and HOFs. Results show that NO₂ group is an effective substituent for enhancing the detonation performance. There exist better correlations between OB and detonation velocities and OB and detonation pressures. The energy gaps between the HOMO and LUMO of the studied compounds are also investigated, and from the data we estimated the relative thermal stability ordering of the title compounds.     

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.     

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 Study of Heterocyclic Nitro Compounds for Use as Novel Explosives and Propellants

The heats of formation (HOFs) of heterocyclic nitro compounds were obtained by using a density functional theory B3LYP method with 6‐31G* and 6‐311+G** basis sets. The isodesmic reactions designed for the evaluation of HOFs keep most of the basic ring structures of the title compounds and thus ensure the credibility of the results. The values of HOFs are 567.90, 874.29 and 975.83 kJ/mol at the B3LYP/6‐31G* level for hexanitrohexazaadamantane ( A ), nonanitrononaza‐tetracyclo[7.3.1.1^3,7.1^5,11] pentadecane ( B ) and tetranitrotetrazacubane ( C ) respectively. The predicted detonation velocities of the title compounds are larger than, and detonation pressures are much larger than that of the widely used 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane (HMX). The dissociation energy for the weakest C‐N bonds in the cage skeleton of the title compounds are 137‐144 kJ/mol at the B3LYP/6‐31G* level.     

Looking for High Energy Density Molecules in the Nitro-substituted Derivatives of Pyridazine

A series of derivatives of pyridazine were designed through substituting hydrogens on the pyridazine ring with nitro groups. To explore the thermal stability of the title molecules, heats of formation, bond dissociation energies, and bond orders were calculated at the B3PW91/6-311+G(d,p) level. To confirm the potential usage as high energy density compounds, the detonation pressure and detonation velocity were predicted by using the empirical Kamlet-Jacobs(K-J) equation. Based on our calculated results, both thermal and kinetic stabilities of the title molecules are confirmed with good detonation characters. Especially, 3,4,5-trinitropyridazide and 3,4,6-trinitropyridazide represent excellent detonation parameters better than 1,3,5-trinitro-1,3,5-triazacyclohexane(RDX) and are screened out as potential high energy density compounds.