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5‐amino‐3‐nitro‐1‐nitramino‐1,2,4‐triazole was synthesized through the nitration reaction of 1,5‐diamino‐3‐nitro‐1,2,4‐triazole, and several energetic salts were prepared based on the reactivity of the acidic proton in nitramino group (−NHNO2). These compounds were fully characterized by NMR (1H and 13C), IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction. Their thermal stabilities were analyzed by differential scanning calorimetric (DSC) and Impact and friction sensitivities were determined using standard BAM technology. Moreover, the structural differences between individual compounds were studied to investigate the potential structure‐property relationship. All compounds possess positive heats of formation calculated based on isodesmic reaction to be between 173.7~454.6 kJ ⋅ mol−1. Among them, 5‐amino‐3‐nitro‐1‐nitramino‐1,2,4‐triazole (D=8682 m ⋅ s−1, P=33.0 GPa, IS=0.75 J), hydrazine salt (D=8908 m ⋅ s−1, P=34.9 GPa, IS=0.5 J) and hydroxylamine salt (D=9117 m ⋅ s−1, P=36.7 GPa, IS=2 J) exhibits desirable detonation properties similar to RDX (D=8795 m ⋅ s−1, P=34.9 GPa), calculated by Kamlet‐Jacobs equations and features comparable impact sensitivity with DDNP (IS=1 J). The simple synthetic route, free of heavy metals and superior detonation properties of above compounds make them serve as promising candidate for green primary explosives. [ABSTRACT FROM AUTHOR]

Density functional theory studies have been performed on a series of highly substituted imidazole and indole derivatives. Heats of formation have been calculated using B3LYP functional with 6-31G basis sets by designing isodesmic reaction conditions. General trend which has been observed in the case of highly substituted imidazoles is that as substitution increases the heat of formation increases. The HOF of 1,2,4,5-tetraphenyl-1H-imidazole is the largest (131.28 kJ/mol) and the HOF of 2-(4-chlorophenyl)-1-benzyl-4,5-diphenyl-1H-imidazole (H) is the smallest (85.82 kJ/mol) at the B3LYP/6-31G level. The relative stability of the substituted imidazoles have been evaluated based on the calculated HOFs and the energy gap between the frontier molecular orbitals. [ABSTRACT FROM AUTHOR]

• Δ f H gas ° for 2- and 8-hydroxy azaazulene and their mercapto analogues were estimated at B3LYP, M06-2X, and G3MP2 levels. • Δ f H gas ° is calculated using atomization and isodesmic reactions. • ketonization/thionization is thermodynamically preferred process. • PA, GB, and DPE for studied structures were calculated at three levels of calculation. • Transfer a proton from keto/thione form is not a preferred process. The gas phase standard enthalpies of formation Δ f H gas ° for the tautomers and rotamers of 2- and 8-hydroxy azaazulene and their mercapto analogues have been estimated at B3LYP/6–311 + G(d,p) and M06-2X/6–311++G(2d,2p) levels of theory. The G3MP2 composite method has also been utilized to obtain more accurate correlated computational results. By using atomization and isodesmic reactions, it has been possible to calculate the theoretical enthalpies of formation for the structures under study. Depending on the enthalpies of formation results, the stability of the examined tautomers and rotamers has been discussed. The gas-phase basicity (GB), proton affinities (PA) of the N and O/S atoms, and the deprotonation enthalpies (DPE) of the NH and OH/SH bonds for the investigated system have been determined at the three levels of theory as well. [ABSTRACT FROM AUTHOR]

Nitro-substituted derivatives of indole were designed by substituting the hydrogen atoms of indole one by one. To explore the thermal stability, the heats of formation were calculated by using the isodesmic reaction and positive values are confirmed for all of them, which indicated their energetic nature. To explore the kinetic stability, the bond dissociation energies are calculated accompanied by the bond orders, and enough kinetic stability is evaluated. To detect the potential application as high-energy-density compounds, the detonation velocity (D), the detonation pressure (P), the explosive heats (Q), and the molecular density (ρ) is calculated further according to the famous Kamlet-Jacobs equation. Based on our calculation, hex-substituted indole has excellent detonation characters (D = 8.80 km/s, P = 35.88 GPa) and can be regarded as high-energy-density compounds for further research. [ABSTRACT FROM AUTHOR]

The ability of three semiempirical methods (PM3, PM5, and PM7) in reproducing the enthalpy of formation (ΔfH°) of polycyclic aromatic phenols (PAPs) was tested by comparing experimental and calculated values for 33 compounds. In addition, the results from the semiempirical methods were compared to those obtained from the suitable isodesmic reactions, performed using the B3LYP–D3 and M06–2X functionals in combination with the 6-311 + G(d,p) basis set. With an average absolute error less than 10 kJ mol−1, all five methodologies yielded mutually comparable results. Considering low computational cost of semiempirical methods, the influence of structural features on ΔfH° of PAPs was investigated using the PM5 and PM7 methods. It was found that the greatest influence on ΔfH° has the size of the molecules, while the effects of other properties, i.e., the position of the OH group, number of bay regions, and molecular branching are weaker. The influence of the OH group position decreases with its moving away from molecular ends, and eventually becomes insignificant. As branching and the number of bay regions are mutually dependent and respective molecules are often nonplanar, it is difficult to examine individual contributions of these two structural features. In general, ΔfH° decreases with increasing number of bay regions and molecular branching. [ABSTRACT FROM AUTHOR]

Various 1,2,5-oxadiazole-1,2,3,4-tetrazole-based high-energy materials were designed and their properties investigated. Their heat of formation, detonation properties, and thermal stability were calculated on the basis of isodesmic reactions, Kamlet-Jacobs equation, and bond dissociation energy, respectively. The results showed that all designed compounds possess high positive heat of formation, and the –N=N–/–N3 substituents were found to be the most effective for improving the heat of formation. The trend of changes in density, detonation pressure, and detonation velocity was almost identical in all compounds, which suggests that density was key to the determination of detonation properties. In view of bond dissociation energy, the –CN/–NH2 substituents improved the thermal stability of the designed compounds, while the other substituents/bridges decreased the stability to some extent. Considering the detonation properties and thermal stability, six compounds (C7, D3, D7, F7, G7, and H7) were selected as potential high-energy materials because they exhibited higher detonation properties and thermal stability than 1,3,5-trinitro-1,3,5-triazinane (RDX). Finally, electronic structures (such as distribution of frontier molecular orbitals and electrostatic potential) of the selected compounds were simulated to obtain detailed information about the electronic structures of the screened compounds. [ABSTRACT FROM AUTHOR]

The DLPNO-CCSD(T1)/CBS and G4 methods combined with isogyric, isodesmic, and homodesmotic working reactions were applied to calculate gas-phase enthalpies of formation for thirty-three C–H–N–O compounds with well-established experimental values. Unlike the G4 method, the DLPNO calculations, even together with isogyric reactions with small reference species, reproduce the experimental enthalpies of formation within chemical accuracy (≈ 4 kJ/mol). For more than half of the compounds, a better accuracy, within 2 kJ/mol, was achieved. These results make the DLPNO-CCSD(T1)/CBS method a promising tool for accurate prediction of enthalpy of formation of medium-sized organic compounds. Being convinced of its reliability, the DLPNO-CCSD(T1)/CBS method was also used to estimate the enthalpies of formation for some challenging compounds with conflicting values reported in the literature (glycerol, nitromethane, nitrobenzene, 1-aminoadamantane, piperazine, and others). [ABSTRACT FROM AUTHOR]

We present a systematic assessment of the density functional tight binding (DFTB) method for calculating heats of formation of fullerenes with isodesmic‐type reaction schemes. We show that DFTB3‐D/3ob can accurately predict ΔfH values of the 1812 structural isomers of C60, reproduce subtle trends in ΔfH values for 24 isolated pentagon rule (IPR) isomers of C84, and predict ΔfH values of giant fullerenes that are in effectively exact agreement with benchmark DSD‐PBEP86/def2‐QZVPP calculations. For fullerenes up to C320, DFTB ΔfH values are within 1.0 kJ mol−1 of DSD‐PBEP86/def2‐QZVPP values per carbon atom, and on a per carbon atom basis DFTB3‐D/3ob yields exactly the same numerical trend of (ΔfH [per carbon] = 722n−0.72 + 5.2 kJ mol−1). DFTB3‐D/3ob is therefore an accurate replacement for high‐level DHDFT and composite thermochemical methods in predicting of thermochemical stabilities of giant fullerenes and analogous nanocarbon architectures. [ABSTRACT FROM AUTHOR]

A combinatorial approach was applied to devise a set of reference Si–C–O–H species that is used to derive group‐additivity values (GAVs) for this class of molecules. The reference species include 62 stable single‐bonded, 19 cyclic, and nine double‐bonded Si–C–O–H species. The thermochemistry of these reference species, that is, the standard enthalpy of formation, entropy, and heat capacities covering the temperature range from 298 to 2000 K was obtained from quantum chemical calculations using several composite methods, including G4, G4MP2, and CBSQB3, and the isodesmic reaction approach. To calculate the GAVs from the ab initio based thermochemistry of the compounds in the training set, a multivariable linear regression analysis is performed. The sensitivity of GAVs to the different composite methods is discussed, and thermodynamics properties calculated via group additivity are compared with available ab initio calculated values from the literature. [ABSTRACT FROM AUTHOR]

Machine learning techniques are increasingly being employed to predict molecular properties. Such models are often trained on large computationally derived datasets, and are only as accurate as the underlying data. We exploit the well-known error cancelling effect of isodesmic and homodesmotic reactions to develop a multi-fidelity data-driven molecular property prediction method. First, we propose an optimization-based scheme to quickly and automatically identify all isofragmented reactions for a target molecule u , i.e., balanced reactions involving u and one or more molecules from a given set of molecules (M), which conserve a predefined set of fragments of arbitrary size. Second, we show that such isofragmented reactions can be leveraged to improve the predictive accuracy of a data-driven model by infusing a small high-accuracy dataset comprising molecules in M. We applied this method with a high-accuracy subset of the NIST thermochemistry database and a simple additive data-driven model trained on a QM9 subset. Our results show that the heats of formation using our method were ∼4.4 kcal/mol more accurate on average than the data-driven model. • An optimization-based method for generalized isofragmented reactions. • Error canceling nature of isofragmented reactions used for multifidelity models. • Method to incorporate isofragmented reactions to correct data-driven models. • A data-driven model for heats of formation improved by 4 kcal/mol. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) has been applied to understand the influence of various linkages on the energetic properties and stability of the polynitro-biphenyl compounds. Structures were optimized using the B3PW91/6-31G(d,p) level, and the heats of formation (HOFs) were computed by employing the selected isodesmic reactions. The results reveal that the –N=N– linkage helps to gain high HOF while the –O–, –NH–C(O)NH–, and –NH–C(O)–C(O)–NH– show a negative impact on energy content. Kamlet-Jacobs (K-J) equations were used to determine detonation properties based on the computed densities and HOFs, while stability and sensitivity were investigated by correlating with the bond dissociation energy (BDE), charge on the nitro group, and the balance parameter on surface potentials. Comparing the effect of different linkages on performance and stability of selected polynitro-biphenyl derivatives reveals that –NH–NH– and –N=N– are suitable for a connection between energetic moieties and these results are expected to demonstrate primary information for designing new energetic materials. [ABSTRACT FROM AUTHOR]

Highlights • There were pure samples dicyclopropyldinitromethane and tricyclopropylmethane. • Energy of combustion of these compounds was determined by calorimetry of combustion. • The enthalpies of vaporization were estimated using electrostatic potential model. • The formation enthalpies of liquid and gas of these compounds were calculated. • Obtained experimental and calculation values of formation enthalpy were compared. Abstract The energies of combustion of liquid dicyclopropyldinitromethane and liquid tricyclopropylmethane were determined by calorimetry of combustion at T = 298.15 K. The enthalpies of vaporization were estimated on the basis of electrostatic potential model. The formation enthalpies of the compounds in liquid and gas states were obtained from these data. The gas enthalpies of formation were also calculated by methods of the group additivity and isodesmic reactions. The obtained experimental and calculation values were compared. [ABSTRACT FROM AUTHOR]

Gas-phase enthalpies of formation of diamantane and some of its derivatives were calculated from isodesmic reactions using adamantane as reference species. The G4 theory was applied to calculate the energies of all molecules involved in the isodesmic reactions. The sublimation enthalpies were predicted by the molecular electrostatic potential (MEP) model. Their values were computed from an equation that describes the relationship between the sublimation enthalpy and computed crystal density, and molecular surface area plus four quantities obtained from the surface electrostatic potential. The coefficients in this equation were determined earlier from least squares fitting to reliable values of sublimation enthalpy of 23 adamantanes. The enthalpy formation of diamantanes in the crystalline phase was estimated on the basis of calculated gas-phase enthalpies of formation and sublimation enthalpies. The difference between experimental and theoretical data and inconsistencies in available experimental data are discussed. [ABSTRACT FROM AUTHOR]

The simplest ideas of antiaromaticity refer to regular monocyclic systems and the eigenfunctions of the Hückel Hamiltonian for 4n electrons in such systems. The antiaromaticity is expressed in the energy penalty for such idealized systems relative to the Hückel energy for 2n noninteracting π pairs. Observed systems seldom achieve the regular planar geometry assumed in this picture, owing to their ability to ease the antiaromaticity penalty by departures from the regular geometry and also by export of the 4n π electrons' charge to substituents. In this report we estimate numerical values for the stabilization derived from such departures from the structure and the charge distribution of the idealized antiaromatic cyclopropenyl anion for a specific case, 3-dehydro-3-methyl carboxylate cyclopropenyl anion 1(-) using the thermochemical scheme CBSQB3 supplemented by CCSD(T) calculations. According to the isodesmic reaction, the anion 1(-) is destabilized by about 10-15 kcal/mol relative to the saturated 3-dehydro-3-methylcarboxylate cyclopropyl anion 2(-). We propose that the anion relieves a portion of the antiaromatic destabilization by (a) pyramidalization of one carbon of the ring, and (b) export of negative charge into the ester substituent. Both of these responses are expressed in the equilibrium structure of the anion. In the course of the study we estimate the acidity of several related anions and the enthalpy of formation of their neutral conjugate acids, and describe the interconversion of 1 to the dehydrotriafulvalene anion 3(-) by reaction with CO2. [ABSTRACT FROM AUTHOR]

The gas-phase enthalpies of formation of four molecules with high flexibility, which leads to the existence of a large number of low-energy conformers, were calculated with the G4 method to see whether the lowest energy conformer is sufficient to achieve high accuracy in the computed values. The calculated values were in good agreement with the experiment, whereas adding the correction for conformer distribution makes the agreement worse. The reason for this effect is a large anharmonicity of low-frequency torsional motions, which is ignored in the calculation of ZPVE and thermal enthalpy. It was shown that the approximate correction for anharmonicity estimated using a free rotor model is of very similar magnitude compared with the conformer correction but has the opposite sign, and thus almost fully compensates for it. Therefore, the common practice of adding only the conformer correction is not without problems. [ABSTRACT FROM AUTHOR]

This paper assesses the performance of quantum chemical models with regard to the calculation of enthalpy of formation of CHON molecules using isodesmic reactions. The high accuracy of prediction of enthalpy of formation of CHON compounds can be achieved by the combination of isodesmic reaction scheme with composite ab initio methods. The best composite methods, such as G4, G4MP2, CBS-QB3, and CBS-APNO, can attain near chemical accuracy or better depending on reaction type. Other composite methods yield the same accuracy only in conjunction with isodesmic or homodesmotic reactions. The DFT and MP2 methods lead to good results if they are used with homodesmotic reactions. For CHO compounds, all composite methods demonstrate the high accuracy not only with isodesmic and homodesmotic reactions, but also with isogyric reactions. Moreover, the DFT and MP2 methods can also yield a high accuracy estimate of the enthalpy of formation when they are used with isodesmic or homodesmotic reactions. Four composite methods (G4, G3, CBS-APNO, and CBS-QB3) employed in conjunction with 45 isogyric reactions yield the enthalpy of formation of hydrazine (97.7 ± 2.0 kJ/mol) in agreement with the best approximating to CCSD(T)/CBS energy, thus calling into question the usually quoted experimental value of 95.5 kJ/mol. [ABSTRACT FROM AUTHOR]

For new high-energy density compounds, a series of new bicyclo[2.2.1]heptane derivatives were designed and studied by density functional theory (DFT) method. The heat of formation (HOF) was evaluated by the isodesmic reaction. The densities and the heats of sublimation were predicted by the electrostatic potential analysis at B3PW91/6-31G(d,p) and B3LYP/6-311++G(2df,2p) levels, respectively. The detonation performances were predicted by the Kamlet-Jacobs equations. The bond dissociation energies (BDE) and impact sensitivity that is evaluated by the free space per molecule were also studied to give a better understanding of the stability. Results show that HOFs increase with the increasing number of N atoms. When the number of NO 2 groups is larger than 4, HOFs generally increase with the increasing number of NO 2 groups. Even though solid-phase HOF is decreasing, detonation energy is always rising with Oxygen Balance (OB) closing to zero-OB, and positive value of OB will largely reduce detonation energy. Detonation velocity and detonation pressure of the designed compounds are in the range of 5.62–9.46 km/s and 11.72–41.44 GPa, respectively. And detonation velocity and detonation pressure always increase with the increasing number of N atoms or NO 2 groups except when OB is positive value. BDEs of all designed compounds are larger than 20 kcal/mol shows that all designed compounds have a reasonable thermal stability. The calculated impact sensitivities show that all designed HEDCs have acceptable sensitivity. Especially impact sensitivity of C7, D7, E7, F6 and G6 are expected to be very close to Tetryl ( h 50 = 25 cm). Considering the thermal stability, impact sensitivity and detonation performance, A8, B8, C7, C8, D7, E7, F6 and G6 might be interesting candidates for use as HEDCs. [ABSTRACT FROM AUTHOR]

Bond dissociation energies (BDEs), radical stabilization energies (RSEs) and the enthalpies of formation (ΔfH°( AA ∙ )) for the Cα-centered radical of 20 common α-amino acids were calculated at the G3MP2 level of theory. In addition, BDEs and ΔfH°( AA ∙ ) for the Cα-centered radicals were calculated via atomization, homolytic, isogyric and isodesmic reactions using 31 reference compounds. RSEs for the α-amino acid radicals reveal a strong captodative effect due to the resonance stabilization. Intramolecular H-bonding and steric repulsion between the side chains and –NH2 and ‒COOH also have an effect on the stability of α-carbon-centered radicals. For the key small reference compounds investigated, the BDEs (ΔfH°( AA ∙ )) computed with isodesmic reactions were found to be quite consistent with each other in terms of mean absolute deviations (MADs) and root-mean-square deviations between 2.0 (2.6) and 3.2 (4.4) kJ mol−1 from experimental data. [ABSTRACT FROM AUTHOR]

Gas-phase O-H homolytic bond dissociation enthalpy in phenol, DH298°(C6H5O-H), is still disputed, despite a large number of experimental and computational studies. In estimating this value, the experimental enthalpy of formation of phenol, ΔfH298°(C6H5OH, g) = -96.4 ± 0.6 kJ/mol (Cox, J. D. Pure Appl. Chem. 1961, 2, 125-128), is often used assuming high accuracy of the experimental value. In the present work a substantially less negative value of ΔfH298°(C6H5OH, g) = -91.8 ± 2.5 kJ/mol was calculated combining G4 theory with an isodesmic reaction approach. A benchmark quality of this result was achieved by using a large number of reliable reference species in isodesmic reaction calculations. Among these are the most accurate ΔfH298° values currently available from the Active Thermochemical Tables (ATcT) for 36 species (neutral molecules, radicals, and ions), anisole with recently reassessed enthalpy of formation, and 13 substituted phenols. The internal consistency of the calculated ΔfH298°(C6H5OH, g) value with the experimental enthalpies of formation of more than 50 reference species suggests that the reported experimental enthalpy of formation of phenol is in error. Taking into account that the enthalpy of formation of phenol has not been investigated experimentally since 1961, the new measurements would be extremely valuable. Using the accurate enthalpies of formation of C6H5OH and C6H5O• calculated in the present work, we obtained DH298°(C6H5O-H) = 369.6 ± 4.0 kJ/mol. This value is in satisfactory agreement with that determined from the most precise experimental measurement. [ABSTRACT FROM AUTHOR]

Heat of formation is one of several important parameters used to assess the performance of energetic compounds. We evaluated the ability of six different methods to accurately calculate gas-phase heat of formation (ΔfH298,go) values for a test set of 45 nitrogen-containing energetic compounds. Density functional theory coupled with the use of isodesmic or other balanced equations yielded calculated results in which 82% (37 of 45) of the ΔfH298,go values were within ±2.0 kcal/mol of the most recently recommended experimental/reference values available. This was compared to a procedure using density functional theory (DFT) coupled with an atom and group contribution method in which 51% (23 of 45) of the ΔfH298,go values were within ±2.0 kcal/mol of these values. The T1 procedure and Benson’s group additivity method yielded results in which 51% (23 of 45) and 64% (23 of 36) of the ΔfH298,go values, respectively, were within ±2.0 kcal/mol of these values. We also compared two relatively new semiempirical approaches (PM7 and RM1) with regard to their ability to accurately calculate ΔfH298,go. Although semiempirical methods continue to improve, they were found to be less accurate than the other approaches for the test set used in this investigation. [ABSTRACT FROM AUTHOR]

The enthalpies of formation for bitetrazole guanidinium salts in the gas and solid phases were calculated using the standard approach and isodesmic reaction method. A comparative analysis of the quality of the methods and the basis sets (HF, 3-21G, 6-31G, 6-311G(d, p); DFT/B3LYP, 3-21G, 6-31G(d)) was performed for the calculation of the molecular volumes necessary for modeling the enthalpies of formation in solid phase, and the optimum set was recommended. The calculated values of enthalpies of formation of the compounds obtained by the isodesmic reaction method are three times lower than the results obtained using standard procedures. [ABSTRACT FROM AUTHOR]

The gas-phase enthalpies of formation ( $${\Delta_{\text{f}}}H_{ 2 9 8}^\circ$$ ) of guanidine and its 10 amino and nitro derivatives were calculated using the isodesmic reaction method at the Gaussian-4 level of theory. The enthalpies of sublimation ( $${\Delta_{\text{sub}}}H_{ 2 9 8}^\circ$$ ) were estimated in the framework of the Politzer approach that combines the empirical equation for enthalpy of sublimation with the B3LYP/cc-pVTZ calculations of the electronic properties of the molecular surfaces. The enthalpies of sublimation of mono-, di-, and triaminoguanidine were also estimated using experimental data for their salts. On the basis of the calculated $${\Delta_{\text{f}}}H_{ 2 9 8}^\circ$$ (g) and $${\Delta_{\text{sub}}}H_{ 2 9 8}^\circ$$ values, the solid-phase enthalpies of formation were estimated for all guanidine derivatives. A predictive model confirms the available experimental data for guanidine, nitroguanidine, and some of their derivatives. The calculated value of solid-phase enthalpy of formation of high-nitrogen energetic compound 3,6-bis(2-nitroguanidino)-1,2,4,5-tetrazine is also in reasonable agreement with the reported experimental values. [ABSTRACT FROM AUTHOR]

The density functional theory (DFT) calculation is performed on 1,1,3,5,5-pentanitro-1,5-bis(difluoramino)-3-azapentane substituted. The heat of formation (HOF) is predicted by B3LYP and B3P86 methods with the 6-311G** and 6-311++G** basis sets via isodesmic reactions. With NF and ONO substitution for NO, HOFs clearly decrease. Furthermore, we designed a detonation reaction for each compound and computed Δ H, the heat of explosion ( Q), and Δ G for each reaction. The general trend is that Q increases as ONO and NO groups are replaced by the NF groups. [ABSTRACT FROM AUTHOR]

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 (NH-N = N-NO). 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. [ABSTRACT FROM AUTHOR]

Density function theory calculations were performed to find comprehensive relationships between the structures and properties of a series of highly energetic polynitroxanthines. The isodesmic reaction method was employed to estimate the gas-phase heat of formation. The solid-state heats of formation for the designed compounds were calculated by the Politzer approach using heats of sublimation. All of the designed compounds were found to possess solid-state heats of formation of >100 kJ mol. Detonation performances were evaluated by the Kamlet-Jacobs equations, based on the predicted densities and solid-state heats of formation. The results indicate that all of the compounds have excellent detonation velocities and pressures. The stabilities of the derivatives were calculated by evaluating their energy gaps, bond dissociation energies, and characteristic heights. The results indicate that all of the compounds have large bond dissociation energies and energy gaps. The characteristic height values of the compounds are more than or close to those of HMX and RDX. Thus, the polynitroxanthine derivatives show good thermodynamic and dynamic stability. Further, the present study may provide useful information on the structure-property relationships of these compounds, and for the development of novel high-energy materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Conformers of nine fluorinated alcohols were determined by theoretical calculations. • Standard enthalpies of formation were predicted from isodesmic reactions. • Enthalpy changes of H-abstraction reactions by OH radicals were computed. • H-abstraction from CH 2 group is the channel thermodynamically most favorable. Molecular conformations, harmonic vibrational frequencies and standard enthalpies of formation for CH 3-n F n CF 2 CH 2 OH, CH 3-n F n CH 2 OH and CH 3-n F n OH (n = 1,2,3) partially fluorinated alcohols were computed at different levels of theory using isodesmic and isogiric work reactions. The lack of data and large uncertainties in the reported thermodynamic properties motivated the present study. As average at the G4 and CBSQB3 levels of theory, standard enthalpies of formation at 298 K of −313.9±1.8, −258.2±1.8 and −208.4±1.8 kcal mol−1 were computed for CF 3 CF 2 CH 2 OH, CHF 2 CF 2 CH 2 OH and CH 2 FCF 2 CH 2 OH, respectively; values of −213.0±1.7, −154.5±1.7 and −100.4±1.7 kcal mol−1 were obtained for CF 3 CH 2 OH, CHF 2 CH 2 OH and CH 2 FCH 2 OH; while −216.9±1.2, −159.8±1.2 and −100.9±1.7 kcal mol−1 were derived for CF 3 OH, CHF 2 OH and CH 2 FOH. The corresponding enthalpies of formation presented here for CF 3 CF 2 CH 2 OH and CH 2 FCF 2 CH 2 OH were predicted for the first time. Hydrogen abstraction reactions enthalpies by OH radicals were also estimated and comparisons with previously reported results were performed. [ABSTRACT FROM AUTHOR]

Density functional theory calculations at B3LYP/6-31G** and B3P86/6-31G** levels were performed to predict the densities ( ρ), detonation velocities (D), pressures (P) and the thermal stabilities for a series of 1,2,4-triazole derivatives for looking 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 position of the subsitutent group has great effect on the BDE and the BDEs of the initial scission step are between 31 and 65 kcal/mol. In addition, the condensed phase heats of formation are also calculated for the title compounds. These results would provide basic information for further studies of HEDCs. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this work, we define an isodesmicity index, which allows the evaluation of the conservation of the error within a given bond conserving reaction. This index is reaction-specific and, therefore, does not rely on the nature of the reference systems. Several aspects of the index are tested, to verify that this measurement shows the desired behavior. The index is a tool, which should allow the user to establish the 'best' bond conserving process for, for instance, the determination of a heat of formation. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: The heat of formation of a number of key C1 and C2 chlorofluorocarbons and hydrochlorofluorocarbons have been calculated by G3, G3MP2, G3MP2B3 and G3B3 methods. Based on the results of the atomization approach, it was found that the errors are approximately dependent upon the number of C–F or C–Cl bonds. Moreover, the bond additive correction (BAC) procedure and isodesmic reactions approach improved the accuracy and decreased these system errors significantly. The extended comparison between the BAC procedure and isodesmic reaction approaches had been made; the latter yielded the best results and showed broader applicability. [Copyright &y& Elsevier]

Quantum chemical calculations are used to compute the heats of formation (HOFs) for 24 nitroester (NE) energetic compounds in which only 5 nitroester energetic compounds have the available experimental heats of formation. The heats of formation of the five compounds are calculated from isodesmic reactions by employing the hybrid density functional theory (DFT) (B3LYP, B3PW91, and B3P86) methods with 6-31G** and 6-311G** basis sets. It is demonstrated that B3PW91/6-31G** method can yield reliable HOFs, which has the mean absolute deviation of 1.1kcal/mol. The HOFs of other 19 nitroester energetic compounds are calculated by using B3PW91/6-31G** method. Through the analysis of the calculated result, it is found that the computed heat of formation decreases when the number of methylene (CH2) group increases for normal chain nitroester compounds. The further study shows that our results about gas-phase heats of formation of nitroester compounds are better than the results of Muthurajan et al. [H. Muthurajan, R. Sivabalan, M.B. Talawar, M. Anniyappan, S. Venugopalan, Prediction of heat of formation and related parameters of high energy materials, J. Hazard. Mater. A133 (2006) 30–45], and Byrd Edward and Rice Betsy [F.C. Byrd Edward, M. Rice Betsy, Improved prediction of heats of formation of energetic materials using quantum mechanical calculations, J. Phys. Chem. A 110 (2006) 1005–1013]. In addition, the condensed phase heat of formation of the nitroester compounds are computed through the same method of Byrd Edward and Rice Betsy. [Copyright &y& Elsevier]

We present density functional theory (DFT) calculations and analysis of some substituted 2,2′, 4,4′, 6,6′- hexanitroazobenzene (HNAB). Geometries of all compounds have been optimized employing by B3LYP method in conjunction with 6-31G** basis set. The heat of formation (Δ f H) is evaluated using isodesmic reaction paths. Density and detonation characteristics including detonation velocity D , detonation pressure P , and detonation energy Q were researched by Kamlet-Jacob equation. We also include study and discuss the relation between sensitivity and molecular/electronic structures. The trigger bonds in the pyrolysis process for HNAB derivatives were calculated and explored. The predicted results indicate that some designed azo bridging (–N N–) compounds outperform traditional energetic materials and may be potential candidates for high-energy materials. [Display omitted] • Substituent effects on the properties related to detonation performance and sensitivity for 2,2′,4,4′,6,6′-hexanitroazobenzene (HNAB) derivatives is proposed. • The sensitivity of HNAB derivatives is explored with molecular/electronic properties. • Several interrelationships of HNAB derivatives is supposed that relate the detonation performance with measured or predicted molecular/electronic properties. Density functional theory (DFT) has been applied to explore the general rules for structure design of azo compounds through energetic properties and stability. Structures of 2,2′, 4,4′, 6,6′- hexanitroazobenzene (HNAB) derivatives were designed and optimized using B3LYP /6-31G(d,p) level, and the heat of formation (Δ f H) were evaluated by constructing isodesmic reactions. Results reveal that the azo bridging (–N N–) is useful for increasing the heat of formation. Kamlet–Jacobs equations were employed to evaluate detonation performance, while the sensitivity was explored by correlating with the bond dissociation energy (BDE), electronic structural parameters (E HOMO , E LUMO , and Δ E LUMO-HOMO), oxygen balance (OB), and charges on nitro group (Q NO2). According to our calculations, some designed HNAB derivatives possess interesting properties, such as good detonation performance and high stability, even beyond RDX and HMX, revealing that the presence of azo bridging (–N N–) backbone together with the introduction of various energetic groups is a promising choice in the design of high energy density materials (HEDMs). [ABSTRACT FROM AUTHOR]

In this work, quantum chemical calculations have been performed on the ionic liquids based on imidazolium, pyridinium, and pyrrolidinium cations with the dicyanamide anion. The dispersion-corrected B3LYP exchange-correlation functional was used to optimize geometries. Enthalpies of formation were calculated at the high-level G3(MP2) theory by employing both the atomization energy and reaction enthalpy approaches. There exists a very good agreement between the predicted enthalpies of formation and available experimental values. For the first time, the enthalpies of formation have been predicted for 21 ion pairs with no available experimental data. The calculated enthalpies of formation are decreased with increasing alkyl chain length. Linear correlations were observed between enthalpy of formation and number of carbon atoms in the alkyl side-chain for all of the studied series of cations. Regardless of the cation type, the contribution of each CH 2 group in the alkyl chain to the enthalpy of formation was also determined. • Enthalpies of formation of dicyanamide based ionic liquids were calculated. • Atomization and isodesmic reactions at the G3(MP2) were used. • Good agreement with experimental data, where available, was achieved. • The calculated enthalpy of formation was found to decrease with increasing alkyl chain length. • A linear correlation was observed between enthalpy of formation and number of carbon atoms in the alkyl side-chain of cations. [ABSTRACT FROM AUTHOR]