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     

DFT Studies on Detonation Properties,Pyrolysis Mechanism,and Stability of the Nitro and Hydroxyl Derivatives of Benzene

Ninety‐one nitro and hydroxyl derivatives of benzene were studied at the B3LYP/6‐31G?? level of density functional theory. Detonation properties were calculated using the Kamlet‐Jacobs equation. Three candidates (pentanitrophenol, pentanitrobenzene, and hexanitrobenzene) were recommended as potential high energy density compounds for their perfect detonation performances and reasonable stability. The pyrolysis mechanism was studied by analyzing the bond dissociation energy (BDE) and the activation energy (E_a) of hydrogen transfer (H–T) reaction for those with adjacent nitro and hydroxyl groups. The results show that E_a is much lower than BDEs of all bonds, so when there are adjacent nitro and hydroxyl groups in a molecule, the stability of the compound will decrease and the pyrolysis will be initiated by the H–T process. Otherwise, the pyrolysis will start from the breaking of the weakest C–NO₂ bond, and only under such condition, the Mulliken population or BDE of the C–NO₂ bond can be used to assess the relative stability of the compound.     

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.     

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.     

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.     

高能化合物热解机理和撞击感度的理论研究-苯和苯胺类硝基衍生物

在DFT-B3LYP/6-31G*水平求得苯和苯胺类硝基衍生物的全优化分子几何和电子结构。通过非限制性 (U) B3LYP/6-31G*计算求得标题物各化学键离解能(BDE)。用UHF-PM3 MO方法求得引发键C-NO2键均裂反应的活化能(Ea)。以静态指标(键集居数、前线轨道能级差和硝基上净电荷)和动态理论指标(BDE和Ea) 阐明了热解引发机理,关联了实验撞击感度。运用SPSS程序关联静态和动态理论指标,表明它们可平行或等价地用作预示标题物的热解引发机理和撞击感度。     

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.     

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.     

Theoretical studies on the structures, thermodynamic properties, detonation properties, and pyrolysis mechanisms of spiro nitramines

Density function theory (DFT) has been employed to study the geometric and electronic structures of a series of spiro nitramines at the B3LYP/6-31G level. The calculated results agree reasonably with available experimental data. Thermodynamic properties derived from the infrared spectra on the basis of statistical thermodynamic principles are linearly correlated with the number of nitramine groups as well as the temperature. Detonation performances were evaluated by the Kamlet-Jacobs equations based on the calculated densities and heats of formation. It is found that some compounds with the predicted densities of ca. 1.9 g/cm3, detonation velocities over 9 km/s, and detonation pressures of about 39 GPa (some even over 40 GPa) may be novel potential candidates of high energy density materials (HEDMs). 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 and the activation energies (E(a)) with the selected PM3 semiempirical molecular orbital (MO) based on the unrestricted Hartree-Fock model. The relationships between BDE, E(a), and the electronic structures of the spiro nitramines were discussed in detail. Thermal stabilities and decomposition mechanisms of the title compounds derived from the B3LYP/6-31G BDE and the UHF-PM3 E(a) are basically consistent. Considering the thermal stability, TNSHe (tetranitrotetraazaspirohexane), TNSH (tetranitrotetraazaspiroheptane), and TNSO (tetranitrotetraazaspirooctane) are recommended as the preferred candidates of HEDMs. These results may provide basic information for the molecular design of HEDMs.     

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.     

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 studies on a series of 1,2,3-triazoles derivatives as potential high energy density compounds

Based on the full-optimized molecular geometric structures at B3LYP/6-31G* and B3P86/6-31G* levels, the densities (ρ), detonation velocities (D), and pressures (P) for a series of 1,2,3-triazole 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 53 and 70 kcal/mol, and 4-nitro-1,2,3-triazole is the most reactive compound, while 1-(2′,4′-dinitrophenyl)-5-nitro-1,2,3-triazole is the least reactive compound for 1,2,3-triazole derivatives studied. The condensed phase heats of formation are also calculated for the title compounds. These results would provide basic information for the further studies of HEDCs. The detonation data of 1-(3′,4′-dinitrophenyl)-4-nitro-1,2,3-triazole and 1-(2′,4′-dinitrophenyl)-4-nitro-1,2,3-triazole show that they meet the requirement for HEDCs.     

Theoretical investigations on structure,density, detonation properties,and sensitivity of the derivatives of PYX

The ? NH₂, ? NO₂, ? N₃, ? NHNO₂, and ? ONO₂ substitution derivatives of PYX (2,6‐bis(picrylamino)‐3,5‐dinitropyridine) were studied at the B3LYP/6‐31G** level of density functional theory. The sublimation enthalpies and heats of formation (HOFs) in gas phase and solid state of these compounds were calculated. The theoretical predicted density (ρ), detonation pressure (P), and detonation velocity (D) showed that these derivatives have better detonation performance than PYX. The effects of substituent groups on HOF, ρ, P, and D were discussed. The order of contribution of various groups to P and D was ? ONO₂ > ? NO₂ > ? NHNO₂ > ? N₃ > ? NH₂. Sensitivity was evaluated using the frontier orbital energies, bond orders, bond dissociation enthalpies (BDEs), and characteristic heights (h₅₀). The trigger bonds in the pyrolysis process for these PYX derivatives may be Ring‐NO₂, NH? NO₂, or O? NO₂ varying with the substituents. The h₅₀ of most compounds are larger than that of CL‐20, and those of ? NH₂, ? NO₂, and most ? ONO₂ derivatives are larger than that of RDX. The BDEs of the trigger bonds of all but the ? ONO₂ derivatives are sufficiently large. Taking both detonation performance and sensitivity into consideration, some derivatives of PYX may be good candidates of explosives. © 2012 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。     

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.     

Inequivalence of substitution pairs in hydroxynaphthaldehyde: A theoretical measurement by intramolecular hydrogen bond strength,aromaticity, and excited‐state intramolecular proton transfer reaction

The inequivalence of substitution pair positions of naphthalene ring has been investigated by a theoretical measurement of hydrogen bond strength, aromaticity, and excited state intramolecular proton transfer (ESIPT) reaction as the tools in three substituted naphthalene compounds viz 1‐hydroxy‐2‐naphthaldehyde (HN12), 2‐hydroxy‐1‐naphthaldehyde (HN21), and 2‐hydroxy‐3‐naphthaldehyde (HN23). The difference in intramolecular hydrogen bond (IMHB) strength clearly reflects the inequivalence of substitution pairs where the calculated IMHB strength is found to be greater for HN12 and HN21 than HN23. The H‐bonding interactions have been explored by calculation of electron density ρ(r) and Laplacian ?²ρ(r) at the bond critical point using atoms in molecule method and by calculation of interaction between σ* of OH with lone pair of carbonyl oxygen atom using NBO analysis. The ground and excited state potential energy surfaces (PESs) for the proton transfer reaction at HF (6‐31G**) and DFT (B3LYP/6‐31G**) levels are similar for HN12, HN21 and different for HN23. The computed aromaticity of the two rings of naphthalene moiety at B3LYP/6‐31G** method also predicts similarity between HN12 and HN21, but different for HN23. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Density functional study of platinum polyyne monomer,oligomer, and polymer: Ground state geometrical and electronic structures

Geometries of monomers and oligomers of a platinum polyyne and its free ligands were optimized using density functional theory with B3LYP hybrid functional. The LANL2DZ basis set was used for Pt and the 6‐31G* for other atoms in geometry optimizations. The electronic structures of these compounds were analyzed using Stuttgart/Dresden ECPs (SDD) basis set for metal atoms and 6‐311G* for others. The polymerization has very little effect on the bond lengths and by introducing the metal, the acetylide bond length increases slightly. The strong overlap between metal sp_x orbitals and σp_x orbitals of acetylides results in localized σ bonding. The hybridization between the ligand pπ orbitals and the platinum dπ orbital resulted in the π‐conjugation enhancement. This conjugation enhancement causes some effects such as the highest‐occupied molecular orbital–lowest‐unoccupied molecular orbital gap reduction and charge transfer characteristic of low‐energy vertical transitions. © 2013 Wiley Periodicals, Inc.     

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).