Heat Of Formation Values Research Articles

Computational investigation and screening of [1,2,4]triazolo[4,3‐b][1,2,4,5]tetrazine‐based high energy materials

SummaryIn the present work, some [1,2,4]triazolo[4,3‐b][1,2,4,5]tetrazine‐based high energy compounds were designed. The electronic structures, heats of formation (HOF), detonation velocities (D), detonation pressures (P), and thermal stabilities (BDEs) of the titled high energy materials were calculated at B3LYP/6‐311G (d,p) theoretical level of DFT method. Based on the calculated data, the frontier molecular orbital energy gaps were from 1.02 (B2) to 3.91 eV (A4), the values of HOF, D, P, and BDEs were from 1020.6 (A4) to 2286.3 kJ mol−1 (D2), from 6.52 (A1) to 9.44 km s−1 (D8), from 17.5 (A1) to 41.5 GPa (D8), and from 36.1 (D2) to 515.5 kJ mol−1 (B1), respectively. Take D, P, and BDEs into consideration, seven compounds (A8, B8, C8, D7, D8, E8, and F8) were screened as potential candidates for high energy materials due to their high detonation properties (D and P) and proper thermal stabilities. Finally, the electronic structures (such as distribution of frontier molecular orbitals and electrostatic potentials) were presented, which may provide a new research direction to high energy materials.

Critical Evaluation of Thermochemical Properties of C1–C4 Species: Updated Group-Contributions to Estimate Thermochemical Properties

A review of literature on enthalpies of formation and molar entropies for alkanes, alkenes, alcohols, hydroperoxides, and their associated radicals has been compiled and critically evaluated. By comparing literature values, the overall uncertainty in thermochemical properties of small hydrocarbons and oxygenated hydrocarbons can be highlighted. In general, there is good agreement between heat of formation values in the literature for stable species; however, there is greater uncertainty in the values for radical species and for molar entropy values. Updated values for a group-additivity method for the estimation of thermochemical properties based on the evaluated literature data are proposed. The new values can be used to estimate thermochemical data for larger, combustion-relevant species for which no calculations or measurements currently exist, with increased confidence.

Quantum-chemical design of tetrazolo[1,5-b][1,2,4,5]tetrazine based nitrogen-rich energetic materials

The molecular structures of azole substituted tetrazolo[1,5-b][1,2,4,5]tetrazine (AsTT) derivatives were designed and fully optimized at the B3PW91/6-31G(d,p) level of theory. Isodesmic reaction was constructed to predict gas phase heat of formation (HOF) and heat of sublimation derived from Politzer approach was used to calculate HOF at condensed phase. The presence of nitrogen-rich AsTT backbone is found promising in increasing the HOF values. Politzer approach also extended to predict the densities of these derivatives from the calculated surface electrostatic properties. Kamlet–Jacobs equations were used to calculate detonation performances based on predicted solid phase heats of formation, densities and gaseous detonation products. The charge distribution on molecular surface and free space per molecule in the unit cell were used to analyze the sensitivity. The explosive power and power index were calculated to assess the potential of designed compounds. According to our calculations, the designed AsTT derivatives possess interesting explosive properties and could be the potential addition in high energy materials (HEMs).

Evaluation of Antioxidant Activity of Tea Polyphenols by a Quantum Chemistry Calculation Method - PM6

Tea polyphenols arepowerful natural antioxidants. To quickly evaluate theantioxidantactivity of these compounds, a quantum chemistry calculation method - PM6 was employed to calculate the heat of formation (HOF). The HOF valuewas negatively correlated well (r= –0.910, RMS=0.12) with the antioxidant activity of flavanols (catechins), flavonols (kaempferol, quercetin, and myricetin), flavanones (dihydromyricetin), anthocyanins (delphinidin, cyanidin, pelargonidin), proanthocyanidins and theaflavins. The number and position of hydroxyl, and the structural groups influencing the conjugation between the B- and C-rings could affect the HOF value and radical scavenging activity of flavonoids. Therefore, the HOF value could be used as a descriptor for modeling antioxidant activity of polyphenols.

Theoretical study of an energetic material di-1H-1,3,4-triazole derivatives

Abstract Computations by density functional theory (DFT) method are performed on a series of di-1H-1,3,4-triazole derivatives with different substituents and linkages. The heat of formation (HOF) is predicted by the designed isodesmic reactions. The predicted results reveal that –N3 and –N N– groups are effective structural units for increasing the HOF values of the di-1H-1,3,4-triazole derivatives. The HOMO–LUMO gap is affected by the substituents and linkage groups. Detonation performance is evaluated using the Kamlet–Jacobs approach based on the calculated density and HOF. The results indicate that –NO2, –NF2, –NH–, –NH–NH– and –N N– groups are helpful for enhancing the detonation properties of di-1H-1,3,4-triazole derivatives. The bond dissociation energy and bond order of the weakest bonds are analyzed to investigate their stability. It is observed that the –CH2–, –CH2–CH2– and –CH CH– groups are effective structural units for improving the stabilities of these derivatives. Considering the detonation performance and the stability, five compounds are screened as the potential candidates for high energy density materials.

DFT Studies on Two Novel Explosives Based on the Guanidine-Fused Bicyclic Structure

Density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) theoretical level were performed for two novel explosives (compounds B and C) based on the guanidine-fused bicyclic skeleton C4N6H8 (A). The heats of formation (HOFs) were calculated via isodesmic reaction. The detonation properties were evaluated by using the Kamlet-Jacobs equations. The bond dissociation energies (BDEs) for the thermolysis initiation bond were also analyzed to investigate the thermal stability. The results show that the compounds have high positive HOF values (B, 1064.68 kJ·mol; C, 724.02 kJ·mol), high detonation properties (ρ, D and P values of 2.04 g·cm and 2.21 g·cm, 9.98 km·s and 10.99 km·s, 46.44 GPa and 59.91 Gpa, respectively) and meet the basic stability requirement. Additionally, feasible synthetic routes of the these high energy density compounds (HEDCs) were also proposed via retrosynthetic analysis.

Prompt NO formation in flames: The influence of NCN thermochemistry

The influence of the route via the NCN radical on NO formation in flames was examined from a thermochemistry and reaction kinetics perspective. A detailed analysis of available experimental and theoretical thermochemical data combined with an Active Thermochemical Tables analysis suggests a heat of formation of 457.8±2.0kJ/mol for NCN, consistent with carefully executed theoretical work of Harding et al. (2008) [5]. This value is significantly different from other previously reported experimental and theoretical values. A combination of an extensively validated comprehensive hydrocarbon oxidation model extended by the GDFkin3.0_NCN-NOx sub-mechanism reproduced NCN and NO mole fraction profiles in a recently characterized fuel-rich methane flame only when heat of formation values in the range of 445–453kJ/mol are applied. Sensitivity analysis revealed that the sensitivities of contributing steps to NO and NCN formation are strongly dependent on the absolute value of the heat of formation of NCN being used. In all flames under study the applied NCN thermochemistry highly influences simulated NO and NCN mole fractions. The results of this work illustrate the thermochemistry constraints in the context of NCN chemistry which have to be taken into account for improving model predictions of NO concentrations in flames.

One pot synthesis, structural and spectral analysis of some symmetrical curcumin analogues catalyzed by calcium oxide under microwave irradiation

A series of sixteen number of curcumin analogues have been synthesized under microwave irradiation using calcium oxide as a catalyst. The synthesized compounds have been characterized using FT-IR, MS, elemental analysis, 1H and 13C NMR spectroscopic techniques. The UV–Vis absorption studies for these compounds have been studied in order to provide the electronic transitions taking place in the molecule. When compared to the curcumin ((1E,4Z,6E)-5-hydroxy-1,7-bis(4-hydroxy-3-methoxyphenyl)hepta-1,4,6-trien-3-one), the absorption maxima, λmax for all the synthesized curcumin analogues with a variety of substituents gets blue shifted i.e., hypsochromic shift was observed. This shift may be assigned to the change of dipole moment within the solvated molecule. Theoretical calculations regarding the optimization of the synthesized molecules, electronic properties like highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and mapped electron density surface diagrams were done. The geometrical energy, dipole moments and heat of formation values have also been calculated using the ArgusLab package by AM1 semi-empirical method.

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 studies on the heats of formation, energetic properties, and thermal stability of energetic nitrogen-rich furazano[3,4-b]pyrazine-based derivatives

The heats of formation (HOF), energetic properties, and thermal stability for a series of furazano[3,4-b]pyrazine derivatives with different substituents or nitrogen-containing heterocycles were studied by using density functional theory. It is found that –N3 or nitrogen-containing heterocycle is an effective structural unit for improving the HOF values of the derivatives. The calculated detonation velocities and detonation pressures indicate that the substitution of –NO2, –NF2, or NO2-substituted heterocycle is very useful for enhancing their detonation performance. An analysis of the bond dissociation energies for several relatively weak bonds suggests that most of the derivatives have good thermal stability. By and large, the N–O bond in the furazano[3,4-b]pyrazine ring is the weakest one and the ring cleavage may happen in thermal decomposition. Considered the detonation performance and thermal stability, three compounds may be considered as the potential candidates of high energy density materials.

Density functional calculation on a high energy density compound having the formula C2OH4−n (NO2) n

A series of ethylene oxide derivations, C2OH4–n (NO2) n (x = 1–4), 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.

Quantum-chemical Investigation of Substituted s-Tetrazine Derivatives as Energetic Materials

s-Tetrazine is the essential candidate of many energetic compounds due to its high nitrogen content, enthalpy of formation and thermal stability. The present study explores the design of s-tetrazine derivatives in which different -NO2, -NH2 and -N3 substituted azoles are attached to the tetrazine ring via C-N linkage. The density functional theory (DFT) is used to predict the geometries, heats of formation (HOFs) and other energetic properties. The predicted results show that azide group plays a very important role in increasing HOF values of the s-tetrazine derivatives. The densities for designed molecules were predicted by using the crystal packing calculations. The introduction of -NO2 group improves the density as compared to -N3, and -NH2 groups and hence the detonation performance. Bond dissociation energy analysis and insensitivity correlations revealed that amino derivatives are better candidates considering insensitivity and stability.

Characterization of nitrogen-bridged 1,2,4,5-tetrazine-, furazan-, and 1H-tetrazole-based polyheterocyclic compounds: heats of formation, thermal stability, and detonation properties

The heats of formation (HOFs), thermal stability, and detonation properties for a series of nitrogen-bridged 1,2,4,5-tetrazine-, furazan-, and 1H-tetrazole-based polyheterocyclic compounds (3,6-bis(1H-1,2,3,4-tetrazole-5-ylamino)-1,2,4,5- tetrazine (TST), 3,6-bis(furazan-5-ylamino)-1,2,4,5-tetrazine (FSF), 3,4-bis(1,2,4,5- tetrazine-3-ylamino)-furazan (SFS), 3,4-bis(1H-1,2,3,4-tetrazole-5-ylamino)-furazan (TFT), 1,5-bis(1,2,4,5-tetrazine-3-ylamino)-1H-1,2,3,4-tetrazole (STS), and 1,5-bis(furazan-3-ylamino)-1H-1,2,3,4-tetrazole (FTF) derivatives) were systematically studied by using density functional theory. The results show that the -N(3) or -NHNH(2) group plays a very important role in increasing the HOF values of the derivatives. Among these series, the SFS derivatives have lower energy gaps, while the TFT derivatives have higher ones. Incorporation of the -NH(2) group into the FSF, SFS, STS, or FTF ring is favorable for enhancing its thermal stability, whereas the substitution of the -NHNH(2) group could increase the thermal stability of the TST, SFS, STS, or FTF ring. The calculated detonation properties indicate that the -NO(2) or -NF(2) is very helpful for enhancing the detonation performance for these derivatives. Considering the detonation performance and thermal stability, six derivatives may be regarded as promising candidates of high-energy density materials (HEDMs). These results provide basic information for the molecular design of novel HEDMs.

Design and selection of nitrogen-rich bridged di-1,3,5-triazine derivatives with high energy and reduced sensitivity

The heats of formation (HOFs), electronic structures, energetic properties, and thermal stabilities of a series of energetic bridged di-1,3,5-triazine derivatives with different substituents and linkages were studied using density functional theory. It was found that the groups -N(3) and -N=N- are effective structural units for improving the HOF values of the di-1,3,5-triazine derivatives. The effects of the substituents on the HOMO-LUMO gap combine with those of the bridge groups. The calculated detonation velocities and detonation pressures indicate that substituting the -ONO(2), -NF(2), or -N=N- group is very useful for enhancing the detonation performance of these derivatives. Analysis of the bond dissociation energies for several relatively weak bonds suggests that most of the derivatives have good thermal stability. On the whole, the -NH(2), -N(3), -NH-, and -CH=CH- groups are effective structural units for increasing the thermal stabilities of the derivatives. Based on detonation performance and thermal stability, nine of the compounds can be considered potential candidates for high energy density materials with reduced sensitivity.

Thermal Diffusivity and Heat of Formation of Harzburgite and Its Major Constituent Minerals

The thermal diffusivity, D, and its temperature dependence of Oman harzburgite rock and its major mineral olivine have been evaluated from the basic properties such as seismic velocities, density, and Debye temperature. The Arrhenius-type temperature dependence of the diffusivity was utilized to evaluate the heat of formation, ΔH D. The diffusivity values, 1.80mm2 · s−1 and 2.1mm2 · s−1 obtained at room temperature for harzburgite and olivine, respectively, are consistent with available data. The diffusivity values for Oman harzburgite are overestimated by an amount of 0.27mm2 · s−1 relative to those of PNG harzburgite. The ΔH D value (−2.40 kJ · mol−1) for harzburgite rock of the Oman ophiolite suite is comparable with that (−2.90 kJ · mol−1) of the harzburgite rock of Papua New Guinea. The disagreements in the thermal diffusivity and heat of formation values may be partly due to ignoring the effect of pyroxene in Oman harzburgite.

Charge transfer on the metallic atom-pair bond and the bond energy

Abstract

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.

Theoretical study of [Si,O,C,O] species: Prediction of new species on triplet potential energy surface

The intermediates [Si,O,C,O] of the Si + CO2 reaction have been studied in detail using high level ab iniitio methods. Both singlet and triplet [Si,O,C,O] species are characterized structurally and energetically. On the singlet potential energy surface (PES), the vdw-OSi–CO isomer and in the triplet PES, the bent-SiOCO isomer is found to be thermodynamically as well as kinetically most stable species. All possible isomerization transition states (TS) are located on both singlet and triplet potential surfaces. On the triplet surface, the stability of the trans-OSiCO isomer is comparable with that of the bent-SiOCO isomer. A non-planar cis-SiOCO isomer is located on the triplet PES, which is predicted for the first time. Heats of formation at 0 K (ΔfH°, 0 K) for all singlet and triplet species are computed using G3B3, G3MP2, and CBS-Q theories. The discrepancy between G3B3 and the other two methods for the heat of formation value for triplet trans-OSiCO is discussed. The PESs for singlet as well as triplet species with their dissociation asymptotes are explored at the CCSD(T)/6-311G(d,p)//MP2/6-311G(d,p) level of theory. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Theoretical Studies on Energetic Property and Stability of Pyrazine and Pyridine Derivatives

AbstractDensity functional calculations at the B3LYP level with 6‐311G** and aug‐cc‐pVDZ basis sets were performed to predict the heats of formation (HOFs) for two pyrazine derivatives and eight pyridine derivatives. In the isodesmic reactions designed for the computation of heats of formation (HOFs), pyrazine and pyridine were chosen as reference compounds. TheN‐oxidations for the ring nitrogen of pyrazine and pyridine derivatives decrease the HOF values whenN‐oxide oxygen is neighboring with amino groups, but increase when it neighbors with nitro groups. Thermal stability was evaluated via bond dissociation energies (BDE) at the UB3LYP/6‐311G** level. As a whole, the homolysis of C–NO2bonds is the main step for bond dissociation of the title compounds. The BDE values of title compounds are influenced by intramolecular hydrogen bonds. The hydrogen bond effects associated with the length of the H···O bonds were analyzed by the electron density at the critical points and natural bond orbital.

A DFT Study on Nitro Derivatives of Pyridine

The heat of formation values of all possible nitro derivatives of pyridine have been calculated by the application of various density functional theory (DFT) methods by a proper isodesmic reaction. The heat of formation data trends in series are found to be independent of the selected DFT method, although some differences have been observed in value. Total energies and nucleus-independent chemical shift (NICS(0)) values have also been calculated in order to jugde the aromatic stabilities for the nitropyridine derivatives. Moreover, a novel topological (Türker-Gümüş, TG) index has been defined for modeling the detonation properties of the explosives.