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.     

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.     

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.     

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.     

Intramolecular hydrogen bonding in 3‐imino‐propenylamine: Theoretical investigations

Intramolecular H‐bonds existing for derivatives of 3‐imino‐propenylamine have been studied using the B3LYP/6‐311++G** level of theory. The nature of these interactions, known as resonance‐assisted hydrogen bonds, has been discussed. Vibrational frequencies for α‐derivatives were calculated at the same level of theory. The topological properties of the electron density distributions for N? H···N intramolecular bridges have been analyzed in terms of the Bader theory of atoms in molecules (AIM). Calculation for 3‐imino‐propenylamine derivatives in water solution were also carried out at B3LYP/6‐311++G** level of theory. Finally, the analysis of hydrogen bond in this molecule and their derivatives by quantum theory of natural bond orbital methods fairly support the ab initio results. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

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.     

DFT study of the C-Cl bond dissociation enthalpies and electronic structure of substituted chlorobenzene compounds

Quantum chemical calculations were used to estimate the bond dissociation energies (BDEs) for 13 substituted chlorobenzene compounds. These compounds were studied by employing the hybrid density functional theory methods (B3LYP, B3PW1, B3P86) with 6-31G** and 6-311G** basis sets. It was demonstrated that B3P86/6-311G** method is the best method for computing the reliable BDEs for substituted chlorobenzene compounds which contain the C-Cl bond. It was found that the C-Cl BDE depends strongly on a computational method and basis set used. Substitution effect on the C-Cl BDE of substituted chlorobenzene compounds is further discussed. It is shown that the effects of substitution on the C-Cl BDE of substituted chlorobenzene compounds are very insignificant. Frontier orbital energy gap of studied compounds was also investigated. From the data on frontier orbital energies gap, we estimated the relative thermal stability of substituted chlorobenzene compounds.     

Conformers and intramolecular hydrogen bonding of the oxalic acid monomer and its anions

Density functional theory, B3LYP/6‐31G** and B3LYP/6‐311+G(2d,p), and ab initio MP2/6‐31G** calculations have been carried out to investigate the conformers, transition states, and energy barriers of the conformational processes of oxalic acid and its anions. QCISD/6‐31G** geometrical optimization is also performed in the stable forms. Its calculated energy differences between the two most stable conformers are very near to the related observed value at 7.0 kJ/mol. It is found that the structures and relative energies of oxalic acid conformers predicted by these methods show similar results, and that the conformer L1 (C_2h) with the double‐interfunctional‐groups hydrogen bonds is the most stable conformer. The magnitude of hydrogen bond energies depends on the energy differences of various optimized structures. The hydrogen bond energies will be about 32 kJ/mol for interfunctional groups, 17 kJ/mol for weak interfunctional groups, 24 kJ/mol for intra‐COOH in (COOH)₂, and 60 kJ/mol for interfunctional groups in (COOH)COO⁻¹ ion if calculated using the B3LYP/6‐311+G(2d,p) method. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 76: 541–551, 2000     

Factors influencing the C?ON bond strength of the alkoxyamines in the styrene–acrylonitrile–TEMPO copolymerization system

Homolytic bond dissociation energy (BDE) of the (C? ON) bond for several N‐alkoxyamines derived from 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) and the corresponding (C? H) bonds were determined from quantum‐mechanical calculations including the B3‐LYP6‐31G(d), B3‐LYP/6‐311++G(2df,p), UB3‐LYP/6‐311+G(3df,2p), and integrated IMOMO (G3:ROMP2/6‐31G(d)) method. The investigated N‐alkoxyamines were considered as models for dormant forms of propagating chains in the radical copolymerization process of styrene with acrylonitrile in the presence of TEMPO according to the terminal and penultimate model. The substituent effect on BDE was investigated. Radical stabilization energies (RSE) for radicals created from homolysis of the investigated N‐alkoxyamines were calculated according to Rüchardt's method. Polar, steric, and stabilization effects on C? ON alkoxyamine bond homolysis were studied. A dramatically weakened C? ON bond in the alkoxyamine‐containing two consecutive styrene units in the propagating chain was ascribed to geometric parameters characterizing energetically unfavorable conformation of the substituents. These phenomena can be regarded as the penultimate effect in the radical living/controlled copolymerization system of styrene with acrylonitrile. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1165–1177, 2008     

Intramolecular hydrogen bond in 3‐imino‐propenylamine isomers: AIM and NBO studies

The molecular structure and intramolecular hydrogen bond energy of 18 conformers of 3‐imino‐propenyl‐amine were investigated at MP2 and B3LYP levels of theory using the standard 6‐311++G** basis set. The atom in molecules or AIM theory of Bader, which is based on the topological properties of the electron density (ρ), was used additionally and the natural bond orbital (NBO) analysis was also carried out. Furthermore calculations for all possible conformations of 3‐imino‐propenyl‐amin in water solution were also carried out at B3LYP/6‐311++G** and MP2/6‐311++G** levels of theory. The calculated geometrical parameters and conformational analyses in gas phase and water solution show that the imine–amine conformers of this compound are more stable than the other conformers. B3LYP method predicts the IMA‐1 as global minimum. This stability is mainly due to the formation of a strong N? H···N intramolecular hydrogen bond, which is assisted by π‐electrons resonance, and this π‐electrons are established by NH2 functional group. Hydrogen bond energies for all conformers of 3‐imino‐propenyl‐amine were obtained from the related rotamers methods. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Intramolecular hydrogen bonding in derivatives of 3‐amino‐propenethial

Intramolecular H‐bonds existing for derivatives of 3‐amino‐propenethial have been studied using the B3LYP/6‐311++G** level of theory. The nature of these interactions, known as resonance assisted hydrogen bonds, has been discussed. The topological properties of the electron density distributions for N—H—S intramolecular bridges have been analyzed in terms of the Bader theory of atoms in molecules. Correlations between the H‐bond strength and topological parameters have been also studied. Furthermore, we obtained the exact value of the intramolecular hydrogen bond energies by the related rotamers method. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Theoretical Study of the N-NO2 Bond Dissociation Energies for Energetic Materials with Density Functional Theory

The N-NO2 bond dissociation energies （BDEs） for 7 energetic materials were computed by means of accurate density functional theory （B3LYP, B3PW91 and B3P86） with 6-31G＊＊ and 6-311G＊＊ basis sets. By comparing the computed energies and experimental results, we find that the B3P86/6-311G＊＊ method can give good results of BDE, which has the mean absolute deviation of 1.30kcal/mol. In addition, substituent effects were also taken into account. It is noted that the Hammett constants of substituent groups are related to the BDEs of the N-NO2 bond and the bond dissociation energies of the energetic materials studied decrease when increasing the number of NO2 group.     

Quantum Monte Carlo calculations of bond dissociation energies for some nitro and amino molecules

Bond dissociation energies (BDEs) for some nitro or amino contained prototypical molecules in energetic materials are computed by fixed‐node diffusion quantum Monte Carlo method. The nodes are determined from a Slater determinant calculated within density functional theory at the B3LYP/6‐311G** level. The possible errors, the nodal error, and the cancellation of nodal errors in calculating BDE are discussed, and the accuracy is compared with other available ab initio computations and experimental results. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

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

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

Substituent effect on intramolecular hydrogen bonding in 2‐hydroxybenzaldehyde

The effect of some substituents on intramolecular hydrogen bonding of 5‐X‐2‐hydroxybenzaldehyde (5‐X‐2‐HBA) has been studied by B3LYP and MP2 methods using 6‐311++G** and AUG‐cc‐PVTZ basis sets. The relationship between hydrogen bond energy E_HB and electron donation (or withdrawal) of substituents has been investigated. An approximately good linear relationship has been detected between Hammett coefficients and hydrogen bond formation energy (R² = 0.98). Herein, population analysis has been performed by atoms in molecules (AIM) and natural bond orbital (NBO) methods. The results of AIM and NBO analyses are in a good agreement with calculated energy values. Furthermore, correlation between ring aromaticity and hydrogen bonding has been investigated by nucleus‐independent chemical shift (NICS) at GIAO/B3LYP/6‐311++G** level of theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Investigation of correlation between impact sensitivities and bond dissociation energies in some triazole energetic compounds

In this article, density functional theory has been utilized to study on the correlation between impact sensitivities h _50% and the bond dissociation energies (BDEs) of nine triazole energetic explosives. By employing B3LYP and B3P86 method with the 6-311G** basis set, all the molecules have been fully optimized. The BDEs for removal of the NO₂ group in these compounds have also been calculated at the same level. Computed results show that BDEs calculated by B3LYP method are all less than those by B3P86 method. The relationship between the impact sensitivities and the weakest C–NO₂ bond dissociation energy (BDE) values have been investigated. The results indicate a good linear correlation between the impact sensitivity h _50% and the ratio (BDE/E) of the weakest BDE to the total energy E.     

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.     

The O···H intramolecular hydrogen bond in 4‐X‐2‐hydroxybenzaldehydes: The relationships between geometrical parameters,estimated binding energies,and NMR data

The relationships among geometrical parameters, estimated binding energies, and nuclear magnetic resonance data in –C?O···H? O? intramolecular H‐bond of some substituted 2‐hydroxybenzaldehyde have theoretically been studied by B3LYP and MP2 methods with 6‐311++G** and AUG‐cc‐PVTZ basis sets. All substituents increase estimated hydrogen bond energies E_HBs (with the exception of NO₂ and C₂H₅), which are in good correlation with geometrical parameters, topological properties of electron density calculated at O···H bond critical points and ring critical points by using atoms in molecules method, the results of natural bond orbital analysis, and calculated nuclear magnetic resonance data. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Density Functional Theory Study of Hydrogen Bonding Dimers with 4-Pyridinecarboxylic Acid Hydrazine

The H‐bonding dimers of 4‐pyridinecarboxylic acid hydrazine were studied using density functional theory (DFT) at B3LYP/6‐311++G** level. The results showed that the most stable dimer D1 had two same linear N H···O hydrogen bonds, and the interaction energy between them was 51.038 kJ·mol⁻¹ which was corrected by the basis set superposition error and zero‐point. The stretching vibration frequency of N H bond had a red shift because of the hydrogen bonds. The natural bond orbital analysis showed that each N H···O hydrogen bond in D1 had the biggest interaction stabilization energy of 69.078 kJ·mol⁻¹. Thermodynamic analysis indicated that the formation process of D1 was exothermic and spontaneous at low and room temperatures.