Heats of formation of organic molecules by Ab Initio calculations: Carboxylic acids and esters

A bond and group equivalent scheme that allows the calculation of heats of formation for carboxylic acids and esters from ab initio 6-31G* energies has been developed. For a group of 16 compounds, the rms error for the calculated heats of formation was 0.64 kcal/mol. Heats of formation have been predicted for an additional seven compounds for which the experimental values are either unknown or suspect. © 1992 by John Wiley & Sons, Inc.     

Evaluation of MINDO/3 calculated structures. II. Branching errors in alkanes and cycloalkanes

MINDO/3 calculations have been carried out for a series of branched chain alkanes in order to assess effects of branching on calculated geometries and heats of formation (ΔH_f). With vicinal branching, MINDO/3 calculates the central C? C bond to be too long. Bond angles are also found to be distorted. Errors in calculated heats of formation are large when geminal branching is present and significant with vicinal branching. Branching error corrections for ΔH_f have been derived and applied to a separate series of branched acyclic and cyclic compounds. For the test sample, application of the branching error corrections gave calculated structures of acyclic branched hydrocarbons with heats of formation having an average absolute error of 1.3 kcal/mole rather than 17.3 kcal/mole before correction. Cyclic branched hydrocarbons are shown to be less well corrected. Calculations of heats of reaction have also been carried out for some isomerization and cyclization reactions using the MINDO/3 and MNDO methods. It is clear from the comparisons that MNDO calculations give less severe errors for highly branched compounds but the errors are still substantial. For prediction of heats of reaction, the error-corrected calculations are shown to be superior to the “raw” calculations obtained by MINDO/3 or MNDO.     

Ground states of molecules. 56. MNDO calculations for molecules containing sulfur

MNDO has been extended to sulfur, but without inclusion of 3d AO s. Calculations are reported for heats of formation, geometries, dipole moments, and ionization energies of a variety of sulfur-containing molecules. The average discrepancy between calculated and observed heats of formation is larger than for compounds of other elements, a difference probably due, at least partly, to the lower accuracy of the thermochemical data for sulfur compounds. The calculated dipole moments agree well with experiment as do the calculated ionization energies, except for those corresponding to ionization from sulfur “lone-pair” orbitals which are too high by ca. 1 eV, probably as a result of the neglect in NDDO of interactions between inner and valence shell orbitals. As in the case of other third-period elements, the calculated heats of formation of compounds of sulfur in its higher valence states (S^IV, S^VI) were too positive by large amounts, due presumably to the neglect of 3d AO s.     

Application of SINDO1 to chlorine and sodium compounds

SINDO1 calculations are presented for ground state geometries, heats of formation, ionization potentials and dipole moments of chlorine and sodium compounds. These calculations are based on a new parametrization of SINDO1 for second-row elements which features inclusion of 3d orbitals and zero point energies. The comparison shows a substantial improvement over MNDO in geometries and heats of formation of hypervalent compounds and ionization potentials, whereas other properties are of similar quality.     

Molecular mechanics studies (MM4) of sulfides and mercaptans

The MM4 force field has been extended to the title class of compounds. The vibrational spectra, structures, conformational equilibria, and heats of formation have been studied for 47 conformers of 29 compounds. In general, the properties may be calculated with accuracy that is competitive with that for hydrocarbons. The structures are better fit than previously because of the inclusion of a torsion–bend interaction term, which has its origin in the lone pair (Bohlmann) effect. Available experimental data do not suffice to yield detailed torsional potentials, or geometries as a function of torsion angle, and these quantities were determined by ab initio calculations at the MP2/6-31G* level. The rms error in the calculated frequencies of seven representative structures (with a total of 64 experimental and 96 ab initio frequencies) is 25 cm⁻¹. The heats of formation for 23 compounds have a weighted rms error of 0.36 kcal/mol. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1827–1847, 1997     

Dynamic differential calorimetry of intermetallic compounds: III. Heats of formation,heats and entropies of fusion of REIn3 and RETl3 compounds

Dynamic differential calorimetry has been employed to evaluate the heats of formation, heats and entropies of fusion of REIn₃ and RETl₃ compounds. The results obtained have been estimated to be corrected to within ±5–6%. The general trend, for both these series, is a decrease in the heat of formation from La to Lu which is correlated with the magnitude of the lanthanide contraction in these compounds. A simple correlation has been found between the heats of formation of REX₃ compounds and the ionic radii of the elements involved.     

Solvent effect in hydrogen-bond formation betweenp-nitrophenol and amines

Thermodynamic characteristics for the 1:1 complex formation reactions ofp-nitrophenol with amines in benzene, chlorobenzene, ando-dichlorobenzene have been derived from combined spectrophotometric equilibrium constant determinations and calorimetric measurements. For cyclohexane as the reaction medium, approximate values of the reaction heats have been calculated from temperature dependences of the equilibrium constants. The results are analyzed in terms of the separately determined heats of transfer of the reactants between the solvents used. Usingp-nitrophenol andp-fluoronitrobenzene as reference compounds, the hydrogen-bond-type interactions ofp-nitrophenol with the aromatic solvents are shown to be accompanied by other specific interactions of comparable strength.     

Theoretical thermochemistry of some LiXHn and BeXHn compounds

Summary In this theoretical work, we consider the geometrical, electronic and energetic properties of some lithium and beryllium derivatives. The standard heats of formation of these compounds have been calculated at the MP4=SDTQ/6-31+G(2df, p)//MP2=FULL/6-31G(d, p) level. The values obtained at this level of the theory are also compared with the heats of formation deduced from a composite procedure in which it is assumed that some corrections can be treated separately and combined in an additive manner. We find that the values determined with the complete 6-31+G(2df, p) basis set are the more accurate.     

Heats of formation of C1?C4 alkyl nitrites (RONO) and their RO-NO bond dissociation energies

The heats of formation of C₃ and C₄ alkyl nitrites (RONO) have been determined via their heats of combustion by bomb calorimetry, thereby providing a complete set of values of ΔHº_f for C₁-C₄ alkyl nitrites. The experimental values are in excellent agreement with values derived from group additivity rules. For branched compounds these calculations involve corrections for gauche interactions. In these cases, the gauche interactions are reflected in the activation energies E₁ determined by recent kinetic studies, required for breaking the RO-NO bond. The heats of formation of the alkoxy radicals involved together with ΔHº_f(NO) = 21.6 kcal/mole leads to the result D(RO-NO) = 41.5 ± 1 kcal/mole. The concordance between D(thermochemical) and D(kinetic), unlike previous kinetic studies, implies that E₂ = 0 ± 1 kcal/mole.     

Extension of MNDO to d orbitals: Parameters and results for the halogens

A recently proposed extension of the MNDO formalism to d orbitals has been parameterized for the halogens CI, Br, and I. Extensive test calculations indicate slight consistent improvements for normalvalent molecules and dramatic improvements for hypervalent molecules, in comparison with established MNDO -type methods without d orbitals. The mean absolute errors in calculated heats of formation are 3.9 kcal/mol for 155 normalvalent compounds and 2.8 kcal/mol for 23 hypervalent compounds. The predicted structures of the hypervalent molecules are qualitatively correct, with a mean absolute error of 2° in 19 bond angles.     

镍、锌、钴(II)-N-(对位取代苯基)亚氨基二乙酸的量热

使用改进的RD-1型热导式量热计测定了镍（Ⅱ）-、钴（Ⅱ）-、锌（Ⅱ）-N-（对位取代苯基）亚氨基二乙酸等三个二元配位体系的生成热．这些配合物的生成热不仅与配体的质子化热之间存在着线性关系，而且它们的大小按金属离子来说是完全符合Irving-Williams序列的，并利用配体的多环水化结构解释了N-（取代苯基）亚氨基二乙酸根质子化热呈正值（吸热）的实验事实。     

Energetic Properties of Rocket Propellants Evaluated through the Computational Determination of Heats of Formation of Nitrogen‐Rich Compounds

The use of ab initio and DFT methods to calculate the enthalpies of formation of solid ionic compounds is described. The results obtained from the calculations are then compared with those from experimental measurements on nitrogen‐rich salts of the 2,2‐dimethyltriazanium cation (DMTZ) synthesized in our laboratory and on other nitrogen‐rich ionic compounds. The importance of calculating accurate volumes and lattice enthalpies for the determination of heats of formation is also discussed. Furthermore, the crystal structure and hydrogen‐bonding networks of the nitroformate salt of the DMTZ cation is described in detail. Lastly, the theoretical heats of formation were used to calculate the specific impulses (I_sp) of the salts of the DMTZ cation in view of a prospective application in propellant formulations.     

Ground states of molecules. 53.MNDO calculations for molecules containing chlorine

MNDO calculations of heats of formation, dipole moments, ionization potentials, and structures are reported for a wide range of compounds containing chlorine in its characteristic valence state (Cl^I) and one or more of the elements H, B, Be, C, N, O, and F. The calculated errors in the heats of formation and the dipole moments are not significantly greater than those previously reported for compounds containing no chlorine. First vertical ionization potentials were on average 0.95 eV too high. The ordering of higher cationic states was found to be correct, even for species such as Cl₂O, Cl₂, and HOCl, where ab initio–Koopmans' theorem calculations predict the incorrect ordering. The calculated energies and geometries of compounds such as CIF₃ are qualitatively incorrect, probably because of the lack of 3d atomic orbitals in the orbital basis set.     

Calorimetric studies of the heats of formation of IIIB-VB adamantine phases

The techniques of precipitation calorimetry and solution calorimetry, with molten tin as the solvent medium, have been used to measure the heats of formation of six IIIB-VB semiconductor compounds. Standard heats of formation of 298 K obtained from these measurements are: AIP (?17.41), AIAs (?14.43), AISb (?5.97), GaP (?12.49), GaAs (?9.76) and InP (?6.75) ?k cal g atom^?1. These and other data are used to examine the validity of published theoretical estimates of the heats of formation of these phases. The interrelation of their heats of atomization and energy band gaps is briefly discussed.     

Design of Energetic Materials Based on Asymmetric Oxadiazole

A new family of asymmetric oxadiazole based energetic compounds were designed. Their electronic structures, heats of formation, detonation properties and stabilities were investigated by density functional theory. The results show that all the designed compounds have high positive heats of formation ranging from 115.4 to 2122.2 kJ mol⁻¹. −N− bridge/−N₃ groups played an important role in improving heats of formation while −O− bridge/−NF₂ group made more contributions to the densities of the designed compounds. Detonation properties show that some compounds have equal or higher detonation velocities than RDX, while some other have higher detonation pressures than RDX. All the designed compounds have better impact sensitivities than those of RDX and HMX and meet the criterion of thermal stability. Finally, some of the compounds were screened as the candidates of high energy density compounds with superior detonation properties and stabilities to that of HMX and their electronic properties were investigated.     

Application of SINDO1 to sulphur compounds

SINDO1 calculations are presented for ground state geometries, heats of formation, ionization potentials and dipole moments. These calculations are based on a new parametrization of SINDO1 for second-row elements which features inclusion of 3d orbitals and zero point energies. The comparison shows an improvement over MNDO, especially for hypervalent sulphur compounds.     

Application of SINDO1 to phosphorus compounds

SINDO1 calculations are presented for ground state geometries, heats of formation, ionization potentials and dipole moments. These calculations are based on a new parametrization of SINDO1 for second-row elements which features inclusion of 3d orbitals and zero point energies. The comparison shows an improvement over MNDO, especially for hypervalent phosphorus compounds.     

MNDO method for calculations of magnesium clusters

A new set of parameters for the magnesium atom has been developed within the MNDO method. In contrast to previously published parameters, the new parameters correctly describe molecules with different chemical natures: magnesium halides, organomagnesium compounds and the recently found small magnesium clusters Mg _n (n=2-8). The average errors in the calculated heats of formation and bond lengths of magnesium compounds, including clusters are: 10.7 kcal/mol and 0.167 Å, respectively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1384–1388, August, 1994.     

Theoretical investigation on the structures,densities, and detonation properties of polynitrotetraazaoctahydroanthracenes

The polynitrotetraazaoctahydroanthracenes were optimized to obtain their molecular geometries and electronic structures at density functional theory–B3LYP/6‐31+G(d) level. Detonation velocities (D) and detonation pressures (P) were estimated for this nitramine compounds using Kamlet‐Jacobs equations, based on the theoretical densities (ρ) and heats of formation. It is found that there are good linear relationships between volume, density, detonation velocity, detonation pressure and the number of nitro group. Thermal stability of the compounds was investigated by calculating the bond dissociation energies and energy gap (ΔE_LUMO–HOMO). The simulation results reveal that molecule H performs similarly to famous explosive RDX. These results provide basic information for molecular design of novel high energetic density compounds. © 2011 Wiley Periodicals, Inc.     

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.