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     

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.     

Comparative theoretical studies of substituted bridged bipyridines and their N-oxides

In this work, the experimental synthesized bipyridines azo-bis(2-pyridine),4,4′-dimethyl-3,3′-dinitro-2,2′-azobipyridine, and N,N′-bis(3-nitro-2-pyridinyl)-methane-diamine and a set of designed bipyridines that have similar frameworks but different linkages and substituents were studied theoretically at the B3LYP/6-31G* level of density functional theory. The gas-phase heats of formation were predicted based on the isodesmic reactions, and the condensed-phase heats of formation and heats of sublimation were estimated in the framework of the Politzer approach. The crystal densities have been computed from molecular packing and results show that incorporation of –N=N–, –N=N(O)–, –CH=N–, and –NH–NH– into bipyridines is more favorable than –CH=CH– and –NH–CH₂–NH– for increasing the density. The predicted detonation velocities (D) and detonation pressures (P) indicate that –NH₂, –NO₂, and –NF₂ can enhance the detonation performance, and –NO₂ and –NF₂ are more favorable. Introducing –N=N–, –N=N(O)–, and –NH–NH– bridge groups into bipyridines is also favorable for improving their detonation performance. The oxidation of pyridine N always but that of –N=N– bridge does not always improve the detonation properties. E4–O, the derivative with –N=N– bridge and two –NF₂ substituent groups, has the largest D (9.90 km/s) and P (47.47 GPa). An analysis of the bond dissociation energies shows that all derivatives have good thermal stability.     

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.     

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 predictions on pentaerythritol tetranitrate-based high energy density compounds

A novel family of pentaerythritol tetranitrate (PETN) derivatives based parent PETN skeleton were designed by introducing two energetic groups –NF₂ and –NO₂. Their electronic structure, heats of formation, detonation properties, impact sensitivity, and thermal stability were investigated by using density functional theory. The findings reveal that most of the title compounds have good detonation performance. The –NF₂ group played an important role in improving the densities, heats of detonation, and detonation properties of the designed molecules. The values of h₅₀ for almost all the PETN derivatives are higher than that of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine. An analysis of bond dissociation energy suggests that the N-NO₂ bond tends to be a trigger bond in thermal decomposition. Taking both detonation properties and thermal stabilities into consideration, the three compounds may be selected as potential high-energy-density compounds.     

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.     

Looking for high‐energy density compounds among hexaazaadamantane derivatives with ?CN, ?NC,and ?ONO2 groups

Density functional theory (DFT) was employed to evaluate the heats of formation (HOFs) for hexaazaadamantane (HAA) derivatives with ? CN, ? NC, and ? ONO₂ groups, respectively. This was done by designing isodesmic reactions at the B3LYP/6‐31G* level of theory, where the HAA cage skeletons were kept unbroken to produce more accurate results, and all HOFs for the required reference compounds, NH₂CN, NH₂NC, NH₂ONO₂, and (CH₂NH)₃, were derived from the G₃ theory calculation based on the atomization energies. The calculation results show that the HOFs of HAA derivatives are mainly affected by the number and the position of substituent groups, all the obtained HOFs are positive, and the ? NC derivatives have the most HOFs among the three types of derivatives with the same number of substituent groups. The detonation velocity (D) and detonation pressure (P) were obtained from the empirical Kamlet–Jacobs equations. All the ? NC and ? CN derivatives of HAA have lower densities (ρ), heats of explosion (Q), D, and P. However, these properties of ? ONO₂ derivatives are rather high and vary with the number of ? ONO₂ groups. Considering the easiness for synthesis and relative stability, 2,4,6,8‐hexaazaadamantanenitrate is finally recommended as a potential candidate of a high‐energy density compound (HEDC). © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Prediction of the properties and thermodynamics of formation for energetic nitrogen‐rich salts composed of triaminoguanidinium cation and 5‐nitroiminotetrazolate‐based anions

Density functional theory and volume‐based thermodynamics calculations were performed to study the effects of different substituents and linkages on the densities, heats of formation (HOFs), energetic properties, and thermodynamics of formation for a series of energetic nitrogen‐rich salts composed of triaminoguanidinium cation and 5‐nitroiminotetrazolate anions. The results show that the ? NO₂, ? NF₂, or ? N₃ group is an effective substituent for increasing the densities of the 5‐nitroiminotetrazolate salts, whereas the effects of the bridge groups on the density are coupled with those of the substituents. The substitution of the group ? NH₂, ? NO₂, ? NF₂, ? N₃, or the nitrogen bridge is helpful for increasing the HOFs of the salts. The calculated energetic properties indicate that the ? NO₂, ? NF₂, ? N₃, or ? N?N? group is an effective structural unit for improving the detonation performance for salts. The thermodynamics of formation of the salts show that all the salts may be synthesized easily by the proposed reactions. The structure‐property relationships provide basic information for the molecular design of novel high‐energy salts. © 2012 Wiley Periodicals, Inc.     

A DFT study of cage compounds: 3, 5, 8, 10, 11, 12-hexanitro-3, 5, 8, 10, 11, 12-hexaazatetracyclo [5.5.1.12,6.04,9] dodecane and its derivatives as high energetic materials

A new cage compound, 3, 5, 8, 10, 11, 12-hexanitro-3, 5, 8, 10, 11, 12-hexaazatetracyclo [5.5.1.1^2,6.0^4,9] dodecane (HNHATCD, I) as well as its –ONO₂ (II) and –N₃ (III) derivatives were proposed in the present work. Their molecular structures were optimized at the B3LYP/6-31G(d,p) level of density functional theory. Heat of formation, strain energy, detonation performance, and thermal stability were studied. Results show that the –N₃ group greatly increases the heat of formation, but decreases the strain energy and density, and it is much more helpful for enhancing the detonation energy than the –NO₂ and –ONO₂ groups. An analysis of bond dissociation energies (BDEs) of the weakest bonds implies that the BDE of –N₃ derivatives is the smallest but it is still larger than 120 kJ mol^?1, revealing that these designed compounds have a high thermal stability. Considering the detonation performance and thermal stability, I and II may be potential candidates of high energy density materials.     

Computational insight into energetic cage derivatives based on hexahydro-1,3,5-trinitro-1,3,5-triazine

Four novel cage compounds were designed by introducing –N(NO₂)CH₂–, –N(NO₂)O–, –N(NO₂)N(NO₂)–, and –N=N– linkages into the RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) skeleton. Their molecular geometry, electronic structure, heat of formation, and detonation properties were systematically studied using density functional theory (DFT). In addition, the most stable dimers of the four compounds were constructed to further investigate their stability based on intermolecular interactions. It is found that the unconventional CH⋯O interactions would be the dominant driving force when the title compounds form crystals. Compared with the traditional explosives, the compounds with higher detonation properties and lower impact sensitivity will be considered as promising candidates for high energy density compounds. Our results indicate that our innovative design strategy is extremely useful for developing novel energetic compounds.     

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     

New theoretically predicted RDX‐ and β‐HMX‐based high‐energy‐density molecules

Theoretically new high‐energy‐density materials (HEDM) in which the hydrogens on RDX and β‐HMX (hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine and octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine, respectively) were sequentially replaced by (N NO₂)x functional groups were designed and evaluated using density functional theory calculations in combination with the Kamlet–Jacobs equations and an atoms‐in‐molecules (AIM) analysis. Improved detonation properties and reduced sensitivity compared to RDX and β‐HMX were predicted. Interestingly, the RDX and β‐HMX derivatives having one attached N NO₂ group [RDX‐(NNO₂)1 and HMX‐(NNO₂)1] showed excellent detonation properties (detonation velocities: 9.529 and 9.575 km·s⁻¹, and detonation pressures: 40.818 and 41.570 GPa, respectively), which were superior to the parent compounds. Sensitivity estimations obtained by calculating impact sensitivities and HOMO‐LUMO gaps indicated that RDX‐(NNO₂)1 and HMX‐(NNO₂)1 were less stable than RDX and HMX but more stable than any of the other derivatives. This method of sequential NNO₂ group attachment on conventional HEDMs offers a firm basis for further studies on the design of new explosives. Furthermore, the newly found structures may be promising candidates for better HEDMs.     

Hydrogen‐Bonding Interactions and Properties of Energetic Nitroamino[1,3,5]triazine‐Based Guanidinium Salts: DFT‐D and QTAIM Studies

The intramolecular hydrogen‐bonding interactions and properties of a series of nitroamino[1,3,5]triazine‐based guanidinium salts were studied by using the dispersion‐corrected density functional theory method (DFT‐D). Results show that there are evident LP(N or O; LP=lone pair)→σ*(N? H) orbital interactions related to O???H? N or N???H? N hydrogen bonds. Quantum theory of atoms in molecules (QTAIM) was applied to characterize the intramolecular hydrogen bonds. For the guanidinium salts studied, the intramolecular hydrogen bonds are associated with a seven‐ or eight‐membered pseudo‐ring. The guanylurea cation is more helpful for improving the thermal stabilities of the ionic salts than other guanidinium cations. The contributions of different substituents on the triazine ring to the thermal stability increase in the order of ? NO₂23 (? ONO₂)2. Energy decomposition analysis shows that the salts are stable owing to electrostatic and orbital interactions between the ions, whereas the dispersion energy has very small contributions. Moreover, the salts exhibit relatively high densities in the range of 1.62–1.89 g cm^?3. The detonation velocities and pressures lie in the range of 6.49–8.85 km s^?1 and 17.79–35.59 GPa, respectively, which makes most of them promising explosives.     

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.     

Comparative Theoretical Studies on Several Energetic Substituted Dioxin-imidazole Derivatives

The molecular structures, infrared spectra, heats of formation (HOFs), detonation properties, chemical and thermal stabilities of several tetrahydro-[1,4]dioxino[2,3-d:5,6-d'] diimidazole derivatives with different substituents were studied using DFT-B3LYP method. The properties of the compounds with different groups such as -NO₂, -NH₂, -N₃, and -ONO₂ were further compared. The -NO₂ and -ONO₂ groups are effective substituents for increasing the densities of the compounds, while the substitution of -N₃ group can produce the largest HOF. The compound with -NO₂ group has the same detonation properties as 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane, while the compound with -ONO₂ group has lower detonation properties than those of hexahydro-1,3,5-trinitro-1,3,5-triazine. The nature bond orbital analysis reveals that the relatively weak bonds in the molecules are the bonds between substituent groups and the molecular skeletons as well as C-O bonds in the dioxin rings. The electron withdrawing groups (-NO₂, -N₃, and -ONO₂) have inductive effects on the linkages between the groups and molecular skeletons. In addition, researches show that the electronegativities of the groups are related with the stabilities of the compounds. Considering detonation performance and thermal stability, the 1,5-dinitro-2,6-bis(trinitromethyl)-3a,4a,7a,8a-tetrahydro-[1,4]dioxino-[2,3-d:5,6-d'] diimidazole satisfies the requirements of high energy density materials.     

Computational investigation of the heat of formation, detonation properties of furazan-based energetic materials

The heats of formation (HOFs) for a series of furazan-based energetic materials were calculated by density functional theory. The isodesmic reaction method was employed to estimate the HOFs. The result shows that the introductions of azo and azoxy groups can increase the HOF, but the introduction of azo group can increase the more HOF, when compared with azoxy group. The detonation velocities and detonation pressures of the furazan-based energetic materials are further evaluated at B3LYP/6-31G* level. Dioxoazotetrafurazan and azoxytetrafurazan may be regarded as the potential candidates of high-energy density materials because of good detonation performance. In addition, there are good linear 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. These results provide basic information for the molecular design of novel high-energy density materials.     

Theoretical investigation of a high density cage compound 1,3,5,7,9,11-hexanitrotetradecahydro-1H-1,3,4,5,7,7b,9,11,12a,12b1,12b2,13-dodecaaza-4,8,12-(epimethanetriyl)cyclohepta[l]cyclopenta[def] phenanthrene

The B3LYP/6-31G** method was used to investigate IR and Raman spectra, heat of formation, and thermodynamic properties of a new designed polynitro cage compound 1,3,5,7,9,11-hexanitrotetradecahydro-1H-1,3,4,5,7,7b,9,11,12a,12b¹,12b²,13-dodecaaza-4,8,12-(epimethanetriyl)cyclohepta[l]cyclopenta[def]phenanthrene. The detonation and pressure were evaluated using the Kamlet–Jacobs equations based on the theoretical density and HOFs. The bond dissociation energies and bond orders for the weakest bonds were analyzed to investigate the thermal stability of the title compound. The results show that N₈–NO₂ bond is predicted to be the trigger bond during pyrolysis. There exists an essentially linear relationship between the WBIs of N–NO₂ bonds and the charges – $ Q_{{{\text{NO}}_{ 2} }} $ on the nitro groups. The crystal structure obtained by molecular mechanics belongs to the P2₁ space group, with lattice parameters Z = 2, a = 11.4658 Å, b = 15.2442 Å, c = 10.2451 Å, ρ = 2.07 g cm^?3. The designed compound has high thermal stability and good detonation properties and is a promising high-energy density compound.     

The effect of terminal substituents on crystal structure,mesophase behaviour and optical property of azo-ester linked materials

A series of azo-ester linked mesogen containing liquid crystalline acrylate compounds C1-C6 having different terminal groups (–F, –Cl, –Br, –OCH₃, –OC₂H₅ and –OC₃H₇) were successfully synthesised and characterised. The chemical structure, purity, thermal stability, mesophase behaviour and optical property of the synthesised compounds were investigated by different instrumental techniques. X-ray crystal structure showed that compounds C1, C4 and C5 exhibited more stable E configuration with two bulky group in the opposite side of the N=N double bond motifs. The fluoro-substituted derivative (C1) is connected by the R¹₂(5) type of C–H…O hydrogen bond motifs whereas the molecules of C4, and C5 are connected to each other by means cyclic R²₂(8) type of C–H…O hydrogen bond motifs. Thermogravimetric study revealed that the investigated compounds exhibited excellent thermal stability. All the compounds showed enantiotropic liquid crystal (LC) phase behaviour and the mesophase formation was greatly influenced by the terminal substituents. Alkoxy (–OCH₃, –OC₂H₅ and –OC₃H₇) substituted compounds exhibited greater mesophase stability than those of halogen (–F, –Cl and –Br) terminated derivatives. UV-vis spectroscopic study revealed that the investigated compounds exhibited a broad absorption band around 300–420 nm with absorption maximum (λ_max) of nearly 370 nm.     

The effect of nitro groups on the structures and energetic properties of the derivatives composed of TATB and cubane

Based on the successful experience of synthesis of the TATB (1, 3, 5-triamino-2, 4, 6-trinitrobenzene) and cubane, we propose to consider their nitro derivatives combined by C–N bond as a series of high energy density compounds. First principles molecular orbital calculations have been used to investigate the structural and energetic properties, including the heat of formation, density, detonation performance, and impact sensitivity. Natural bond orbital analysis was carried out to investigate the influence of substituents on the electron delocalization. The results implied that the inclusion of nitro group will decrease the stability of cage skeleton and weaken the C–NO₂ bond. The calculated heats of formation, density, detonation velocity, and detonation pressure are positive and large. The results revealed that two of five derivatives have the close performance and sensitivity to those of CL-20, indicating that they may be explored as new potential high energy materials. Leave them with the notable value to dig out.