Theoretical investigation on the heats of formation and detonation performance in polydinitroaminocubanes

A series of polydinitroaminocubanes have been designed computationally. We calculated the heats of formation, the detonation velocity (D) and detonation pressure (P) of the title compounds by density function theory (DFT) with 6-311?G** basis set. The relationship between the heats of formation and the molecular structures is discussed. The result shows that all cubane derivatives have high and positive heats of formation, which increase with increasing number of dinitroamino groups. The detonation performances of the title compound were estimated by Kamlet-Jacobs equation, and the result indicated that most cubane derivatives have good detonation performance over RDX (hexahydro-1,3,5-trinitro-1,3,5-trizine) and HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane). In addition, we also found that the heat of detonation (Q) is another very important impact in increasing detonation performance except density. The relative stabilities of the title compound are discussed in the terms of the calculated heats of formation, and the energy gaps between the frontier orbitals. The results have not only shown that these compounds may be used as high energy density compounds (HEDCs), but also provide some useful information for further investigation.     

Density functional study on the derivatives of purine

The derivatives of purine are designed through substituting the hydrogen atoms on it for nitro and amino functional groups. Geometries and frequency are analyzed at the B3LYP/6-31 G** level of density functional theory(DFT). Heats of formation (HOF), bond dissociation energy(BDE) and detonation parameters (detonation velocity and detonation pressure) are obtained in detail at the same level. It is found that the BDE values of all derivatives are over 120KJ·mol(-1), and have high positive heats of formation. These derivatives possess excellent detonation properties, for B1, B2, and C, the detonation velocity are 9.58, 9.57,and 9.90 km·s(-1), and the detonation pressure are 43.40,46.05, and 46.37 Gpa, respectively, the detonation performances are better than cyclotrimethylenetrinitramine (RDX)and cyclotetramethylenetetranitramine (HMX). Hence, the derivations of purine may be promising well-behaved high energy density materials.     

Density functional calculations for a high energy density compound of formula C6H6?n (NO2) n

A series of polynitroprismanes, C(6)H(6-n )(NO(2))(n) (n?=?1-6) intended for use as high energy density compounds (HEDCs) were designed computationally. Their electronic structures, heats of formation, interactions between nitro groups, specific enthalpies of combustion, bond dissociation energies, and explosive performances (detonation velocities and detonation pressures) were calculated using density functional theory (DFT) with the 6-311 G** basis set. The results showed that all of the polynitroprismanes had high positive heats of formation that increased with the number of substitutions for the prismane derivatives, while the specific enthalpy of combustion decreased as the number of nitro groups increased. In addition, the range of enthalpy of combustion reducing is getting smaller. Interactions between ortho (vicinal) groups deviate from the group additivity rule and decrease as the number of nitro groups increases. In terms of thermodynamic stability, all of the polynitroprismanes had higher bond dissociation energies (BDEs) than RDX and HMX. Detonation velocities and detonation pressures were estimated using modified Kamlet-Jacobs equations based on the heat of detonation (Q) and the theoretical density of the molecule (ρ). It was found that ρ, D, and P are strongly linearly related to the number of nitro groups. Taking both their energetic properties and thermal stabilities into account, pentanitroprismane and hexanitroprismane are potential candidate HEDCs.     

Looking for high energy density compounds among polynitraminecubanes

Based on fully optimized geometric structures at DFT-B3LYP/6-311G** level, we calculated electronic structures, heats of formation, strain energies, bond dissociation energies and detonation performance (detonation velocity and detonation pressure) for a series of polynitraminecubanes. Our results have shown that energy gaps of cubane derivatives are much higher than that of triaminotrinitrobenzene (TATB), which means that cubane derivatives may be more sensitive than TATB. Polynitraminecubanes have high and positive heats of formation, and a good linear relationship between heats of formation and nitramine group numbers was presented. As the number of nitramine groups in the molecule increases, the enthalpies of combustion values are increasingly negative, but the specific enthalpy of combustion values decreases. It is found that all cubane derivatives have high strain energies, which are affected by the number and position of nitramine group. The calculated bond dissociation energies of C-NHNO₂ and C-C bond show that the C-C bond should be the trigger bond in the pyrolysis process. It is found that detonation velocity (D), detonation pressure (P) and molecule density (ρ) have good linear relationship with substituented group numbers. Heptanitraminecubane and octanitraminecubane have good detonation performance over 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX), and they can be regarded as potential candidates of high energy density compounds (HEDCs). The results have not only shown that these compounds may be used as HEDCs, but also provide some useful information for further investigation.     

Dinitroamino benzene derivatives: a class new potential high energy density compounds

Dinitroamino benzene derivatives are designed and studied in detail with quantum chemistry method. The molecular theory density, heats of formation, bond dissociation energies, impact sensitive and detonation performance are investigated at DFT-B3LYP/6-311G** level. The results of detonation performance indicated most of the compounds have better detonation velocity and pressure than RDX and HMX. The N-N bond can be regard as the trigger bond in explosive reaction, and the bond dissociation energies of trigger bond are almost not affected by the position and number of substituent group. The impact sensitive are calculated by two different theory methods. It is found that the compounds, which can become candidates of high energy materials, have smaller H₅₀ values than RDX and HMX. It is hoped that this work can provide some basis information for further theory and experiment studies of benzene derivatives.     

Theoretical studies on nitrogen rich energetic azoles

Different nitro azole isomers based on five membered heterocyclics were designed and investigated using computational techniques in order to find out the comprehensive relationships between structure and performances of these high nitrogen compounds. Electronic structure of the molecules have been calculated using density functional theory (DFT) and the heat of formation has been calculated using the isodesmic reaction approach at B3LYP/6-31G* level. All designed compounds show high positive heat of formation due to the high nitrogen content and energetic nitro groups. The crystal densities of these energetic azoles have been predicted with different force fields. All the energetic azoles show densities higher than 1.87 g/cm³. Detonation properties of energetic azoles are evaluated by using Kamlet-Jacobs equation based on the calculated densities and heat of formations. It is found that energetic azoles show detonation velocity about 9.0 km/s, and detonation pressure of 40GPa. Stability of the designed compounds has been predicted by evaluating the bond dissociation energy of the weakest C-NO₂ bond. The aromaticity using nucleus independent chemical shift (NICS) is also explored to predict the stability via delocalization of the π-electrons. Charge on the nitro group is used to assess the impact sensitivity in the present study. Overall, the study implies that all energetic azoles are found to be stable and expected to be the novel candidates of high energy density materials (HEDMs).     

Is 1-nitro-1-triazene a high energy density material?

An azo bridge (–N?=?N–) can not only desensitize explosives but also dramatically increase their heats of formation and explosive properties. Amino and nitro are two important high energy density functional groups. Here, we present calculations on 1-nitro-1-triazene (NH₂–N?=?N–NO₂). Thermal stability and detonation parameters were predicted theoretically at CCSD(T)/6-311G* level, based on the geometries optimized at MP2/6-311G* level. It was found that the p?→?π conjugation interaction and the intramolecular hydrogen bonding that exist in the system together increase the thermal stability of the molecule. Moreover, the detonation parameters were evaluated to be better than those of the famous HMX and RDX. Finally, the compound was demonstrated to be a high energy density material.     

Quantum chemical studies on the aminopolynitropyrazoles

We have explored the geometric and electronic structures, band gap, thermodynamic properties, density, detonation velocity and detonation pressure of aminopolynitropyrazoles using the density functional theory (DFT) at the B3LYP/aug-cc-pVDZ level. The calculated detonation velocity and detonation pressure, stability and sensitivity of model compounds appear to be promising compared to the known explosives 3,4-dinitro-1 H-pyrazole (3,4-DNP), 3,5-dinitro-1 H-pyrazole (3,5-DNP), hexahydro-1,3,5-trinitro-1,3,5-triazinane (RDX) and octahydro-1,3,5,7-tetranitro-l,3,5,7-tetraazocane (HMX). The position of NH₂ group in the polynitropyrazoles presumably determines the structure, stability, sensitivity, density, detonation velocity and detonation pressure.     

Computational design and structure–property relationship studies on heptazines

This study aimed to design novel nitrogen-rich heptazine derivatives as high energy density materials (HEDM) by exploiting systematic structure–property relationships. Molecular structures with diverse energetic substituents at varying positions in the basic heptazine ring were designed. Density functional techniques were used for prediction of gas phase heat of formation by employing an isodesmic approach, while crystal density was assessed by packing calculations. The results reveal that nitro derivatives of heptazine possess a high heat of formation and further enhancement was achieved by the substitution of nitro heterocycles. The crystal packing density of the designed compounds varied from 1.8 to 2 g cm⁻³, and hence, of all the designed molecules, nitro derivatives of heptazine exhibit better energetic performance characteristics in terms of detonation velocity and pressure. The calculated band gap of the designed molecules was analyzed to establish sensitivity correlations, and the results reveal that, in general, amino derivatives possess better insensitivity characteristics. The overall performance of the designed compounds was moderate, and such compounds may find potential applications in gas generators and smoke-free pyrotechnic fuels as they are rich in nitrogen content.     

Comparative theoretical studies of differently bridged nitramino-substituted ditetrazole 2-<Emphasis Type="Italic">N</Emphasis>-oxides with high detonation performance and an oxygen balance of around zero

In this work, six (A–F) nitramino (–NHNO₂)-substituted ditetrazole 2-N-oxides with different bridging groups (–CH₂–, –CH₂–CH₂–, –NH–, –N=N–, and –NH–NH–) were designed. The six compounds were based on the parent compound tetrazole 2-N-oxide, which possesses a high oxygen balance and high density. The structure, heat of formation, density, detonation properties (detonation velocity D and detonation pressure P), and the sensitivity of each compound was investigated systematically via density functional theory, by studying the electrostatic potential, and using molecular mechanics. The results showed that compounds A–F all have outstanding energetic properties (D: 9.1–10.0 km/s; P: 38.0–46.7 GPa) and acceptable sensitivities (h ₅₀: 28–37 cm). The bridging group present was found to greatly affect the detonation performance of each ditetrazole 2-N-oxide, and the compound with the –NH–NH– bridging group yielded the best results. Indeed, this compound (F) was calculated to have comparable sensitivity to the famous and widely used high explosive 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), but with values of D and P that were about 8.7% and 19.4% higher than those for HMX, respectively. The present study shows that tetrazole 2-N-oxide is a useful parent compound which could potentially be used in the design of new and improved high-energy compounds to replace existing energetic compounds such as HMX.     

Molecular design of aminopolynitroazole-based high-energy materials

The density functional theory (DFT) was employed to calculate the energetic properties of several aminopolynitroazoles. The calculations were performed to study the effect of amino and nitro substituents on the heats of formation, densities, detonation performances, thermal stabilities, and sensitivity characteristics of azoles. DFT-B3LYP, DFT-B3PW91, and MP2 methods utilizing the basis sets 6-31 G* and 6-311 G (2df, 3p) were adopted to predict HOFs via designed isodesmic reactions. All of the designed aminopolynitroazoles had heats of formation of >220 kJ mol(-1). The crystal densities of the aminopolynitroazoles were predicted with the cvff force field. All of the energetic azoles had densities of >1.83 g/cm(3). The detonation velocities and pressures were evaluated using the Kamlet-Jacobs equations, utilizing the predicted densities and heats of formation. It was found that aminopolynitroazoles have a detonation velocity of about 9.1 km/s and detonation pressure of 36 GPa. The bond dissociation energies for the C-NO(2) and N-NO(2) bonds were analyzed to investigate the stabilities of the designed molecules. The charge on the nitro group was used to assess impact sensitivity in the present study. The results obtained imply that the designed molecules are stable and are expected to be candidates for high-energy materials (HEMs).     

Theoretical insights into the stabilities,detonation performance,and electrostatic potentials of cocrystals containing α- or β-HMX and TATB,FOX-7, NTO,or DMF in various molar ratios

A molecular dynamics method was employed to study the binding energies associated with the cocrystallization (at selected crystal planes) of either 1,3,5-triamino-2,4,6-trinitro-benzene (TATB), 1,1-diamino-2,2-dinitroethylene, 3-nitro-1,2,4-triazol-5-one (TATB, FOX-7, and NTO, respectively, all of which are explosives), or N,N-dimethylformamide (DMF, a nonenergetic solvent) in various molar ratios with 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane in its α and β conformations (α-HMX and β-HMX, respectively). The results showed that the cocrystals with low molar ratios (2:1, 1:1, 1:2, and 1:3) were the most stable. The binding energies of HMX/NTO and HMX/DMF were larger than those of HMX/TATB and HMX/FOX-7. According to the calculated stabilities, HMX prefers to adopt its α form in HMX/TATB and its β form in HMX/NTO, whereas the two forms coexist in HMX/FOX-7. For HMX/TATB, HMX/NTO, and α-HMX/FOX-7, increasing the proportion of the cocrystal component with the highest detonation heat (HMX in the first two cases, FOX-7 in the latter) increases the detonation heat, velocity, and pressure of the cocrystal. However, increasing the proportion of the component with the highest detonation heat in β-HMX/FOX-7 and γ-CL-20/FOX-7 increases the detonation heat of the cocrystal but decreases its detonation velocity. An investigation of the surface electrostatic potential revealed how the sensitivity changes upon cocrystal formation.

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Graphical Abstract Surface electrostatic potential of HMX/TATB

     

Molecular design of new nitramine explosives: 1,3,5,7-tetranitro-8-(nitromethyl)-4-imidazolino[4,5-b]4-imidazolino-[4,5-e] pyridine and its N-oxide

Two new nitramine compounds containing pyridine, 1,3,5,7-tetranitro-8-(nitromethyl) -4-imidazolino[4,5-b]4-imidazolino-[4,5-e]pyridine and its N-oxide 1,3,5,7-tetranitro-8- (nitromethyl)-4-imidazolino[4,5-b]4-imidazolino-[4,5-e]pyridine-4-ol were proposed. Density functional theory (DFT) has been employed to study the molecular geometries, electronic structures, infrared spectra, and thermodynamic properties at the B3LYP/6-31G* level. Their detonation performances evaluated using the Kamlet-Jacobs equations with the calculated densities and heats of formation are superior to those of HMX. The predicted densities of them were ca. 2 g*cm^-3, detonation velocities were over 9 km*s^-1, and detonation pressures were about 40 GPa, showing that they may be potential candidates of high energy density materials (HEDMs). The natural bond orbital analysis indicated that N-NO₂ bond is the trigger bond during thermolysis process. The stability of the title compounds is slightly lower than that of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12- hexaazaisowurtzitane (CL-20). The results of this study may provide basic information for the molecular design of new HEDMs.     

Theoretical studies on the thermodynamic properties, densities, detonation properties, and pyrolysis mechanisms of trinitromethyl-substituted aminotetrazole compounds

Trinitromethyl-substituted aminotetrazoles with –NH₂, –NO₂, –N₃, and –NHC(NO₂)₃ groups were investigated at the B3LYP/6-31G(d) level of density functional theory. Their sublimation enthalpies, thermodynamic properties, and heats of formation were calculated. The thermodynamic properties of these compounds increase with temperature as well as with the number of nitro groups attached to the tetrazole ring. In addition, the detonation velocities and detonation pressures of these compounds were successfully predicted using the Kamlet–Jacobs equations. It was found that these compounds exhibit good detonation properties, and that compound G (D = 9.2 km/s, P = 38.8 GPa) has the most powerful detonation properties, which are similar to those of the well-known explosive HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocine). Finally, the electronic structures and bond dissociation energies of these compounds were calculated. The BDEs of their C–NO₂ bonds were found to range from 101.9 to 125.8 kJ/mol^-1. All of these results should provide useful fundamental information for the design of novel HEDMs.     

Comparative theoretical studies of energetic pyrazole-pyridine derivatives

The pyrazole-pyridine derivatives were optimized to obtain their molecular geometries and electronic structures at the DFT-B3LYP/6-31G(d,p) and DFT-B3P86/6-31G(d,p) levels. Molecular mechanics (MM) calculations were performed for the title compounds. Heats of formation (HOFs) were predicted through designed isodesmic reactions. Detonation performance was evaluated by using the Kamlet-Jacobs equations based on the calculated densities and heats of formation. The thermal stability of the title compounds was investigated via the bond dissociation energies (BDEs). The simulation results reveal that the compound with one pyrazole ring that is fully nitro-substituted performs similarly to the famous explosive HMX, and the compound with two pyrazole rings that are fully nitro-substituted outperforms HMX. According to the quantitative standard of energetics and stability as high energy density materials (HEDMs), the compound with two pyrazole rings that are fully nitro-substituted essentially satisfies this requirement.     

Theoretical investigation on detonation performances and thermodynamic stabilities of the prismane derivatives

Based on DFT-B3LYP/6-311G** method, the molecular geometric structures of polynitramineprismanes are fully optimized. The detonation performances, energy gaps, strain energies, as well as their stability were investigated to look for high energy density compounds (HEDCs). Our results show that all polynitramineprismanes have high and positive heat of formation. To construct the relationship between stabilities and structures, energy gaps and bond dissociation energies are calculated, and these results show that the energy gaps of prismane derivatives are much higher than that of TATB (0.1630). In addition, the C-C bonds on cage are confirmed as trigger bond in explosive reaction. All polynitramineprismanes have large strain energies, and the strain energies of all compounds are slightly smaller than prismane, which indicated that the strain energies were somewhat released compared to prismane. Considering the quantitative criteria of HEDCs, hexanitramineprismane is a good candidate of high energy compounds.     

Theoretical studies on the crystal structure, thermodynamic properties, detonation performance and thermal stability of cage-tetranitrotetraazabicyclooctane as a novel high energy density compound

The B3LYP/6-31G (d) method of density functional theory (DFT) was used to study molecular geometry, electronic structure, infrared spectrum (IR) and thermodynamic properties. The heat of formation (HOF) and calculated density were estimated to evaluate the detonation properties using Kamlet–Jacobs equations. Thermal stability of 3,5,7,10,12,14,15,16-octanitro- 3,5,7,10,12,14,15,16-octaaza-heptacyclo[7.5.1.1^2,8.0^1,11.0^2,6.0^4,13.0^6,11]hexadecane (cage-tetranitrotetraazabicyclooctane) was investigated by calculating the bond dissociation energy (BDE) at unrestricted B3LYP/6-31G (d) level. The calculated results show that the N–NO₂ bond is a trigger bond during thermolysis initiation process. The crystal structure obtained by molecular mechanics (MM) methods belongs to Pna2₁ space group, with cell parameters a?=?12.840 Å, b?=?9.129 Å, c?=?14.346 Å, Z?=?6 and ρ?=?2.292 g·cm^?3. Both the detonation velocity of 9.96 km·s^?1 and the detonation pressure of 47.47 GPa are better than those of CL-20. According to the quantitative standard of energetics and stability, as a high energy density compound (HEDC), cage-tetranitrotetraazabicyclooctane essentially satisfies this requirement.     

Theoretical study on benzoheterocycle based energetic materials,effect of heterocyclic-fused,conjugation, hydrogen bond,and substitutional group on the detonation performance

In this paper, four series of benzoheterocycle based energetic materials (EMs) have been designed to plan out a strategy to improve the density and safety of EMs, such as combining the insensitive group with aminobenzene ring and the high energetic nitramine explosives, benzo-heterocycle mother ring, designing multi-nitrogen heterocycles with a conjugated system containing N-N and C-N high energy bonds, and hydrogen bonding. Their optimized structure and detonation properties were first calculated and discussed using DFT methods. After calculation, these designed explosives all showed good detonation from 7352 m/s to 8788 m/s. Among them, the compounds with six nitro groups, 1c, 2c, 3c, and 4c, exhibit better performance and rather poor impact sensitivity. However, we found that the compounds with five nitro groups and one amino group have a limited performance reduction and a rapid stability improvement. These four compounds, 1b, 2b, 3b, and 4b, have good detonation performance and better stability. Moreover, the synthesis routes for these four compounds were also designed. The precursor 4–0 and mononitro product 4–1 were successfully synthesized. Their 1H NMR, single crystal, and elemental analysis were also done to verify the structures.     

DFT study on the structure and explosive properties of nitropyrazoles

Ab initio molecular orbital calculations at the B3LYP/aug-cc-pVDZ level have been carried out to explore the structure, stability, sensitivity and band gap of nitropyrazoles. Kamlet and Jacob equations were used to calculate the detonation velocity and detonation pressure of designed compounds. The explosive properties of polynitropyrazole-N-oxides appear to be higher compared with those of octanitrocubane and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexa azaisowurtzitane. The sensitivity, heat of explosion, density, detonation velocity and detonation pressure are presumably related to the number and the relative positions of NO₂ groups on the pyrazole ring.     

Theoretical studies on the structure, thermochemical and detonation properties of amino and nitroso substituted 1,2,4-triazol-5-one-N-oxides

DFT calculations at the B3LYP/aug-cc-pVDZ level have been carried out to explore the structure, stability, electron density, heat of formation, detonation velocity and detonation pressure of substituted amino- and nitroso-1,2,4-triazol-5-one-N-oxides. Heats of formation of substituted triazol-5-one-N-oxides have been computed at the B3LYP/aug-cc-pVDZ level via isodesmic reaction procedure. Materials Studio 4.1 package was used to predict the crystal density of model compounds. Kamlet-Jacob equations were used to calculate detonation properties based on the calculated heat of explosion and crystal density. The designed compounds 4, 6, 7 and 8 have shown higher performance compared with those of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane and octanitrocubane. Atoms-in-molecule (AIM) analyses have also been carried out to understand the nature of intramolecular interactions in the designed molecules.