Accurate thermochemical properties for energetic materials applications. II. Heats of formation of imidazolium-, 1,2,4-triazolium-, and tetrazolium-based energetic salts from isodesmic and lattice energy calculations

A computational approach to the prediction of the heats of formation (DeltaH(f)degrees' s of solid-state energetic salts from electronic structure and volume-based thermodynamics (VBT) calculations is described. The method uses as its starting point reliable DeltaH(f)degrees' s for energetic precursor molecules and ions. The DeltaH(f)degrees' s of more complex energetics species such as substituted imidazole, 1,2,4-triazole, and tetrazole molecules and ions containing amino, azido, and nitro (including methyl) substituents are calculated using an isodesmic approach at the MP2/complete basis set level. On the basis of comparisons to experimental data for neutral analogues, this isodesmic approach is accurate to <3 kcal/mol for the predicted cation and anion DeltaH(f)degrees' s. The DeltaH(f)degrees' s of the energetic salts in the solid state are derived from lattice energy (U(L)) calculations using a VBT approach. Improved values for the alpha and beta parameters of 19.9 (kcal nm)/mol and 37.6 kcal/mol for the U(L) equation were obtained on the basis of comparisons to experimental U(L)' s for a series of 23 salts containing ammonium, alkylammonium, and hydrazinium cations. The total volumes are adjusted to account for differences between predicted and experimental total volumes due to different shapes of the ions (flat vs spherical). The predicted DeltaH(f)degrees' s of the energetic salts are estimated to have error bars of 6-7 kcal/mol, on the basis of comparisons to established experimental DeltaH(f)degrees' s of a subset of the salts studied. Energetic salts with the highest positive DeltaH(f)degrees' s are predicted for azido-containing cations, coupled with heterocyclic anions containing nitro substituents. The substitution of functional groups on carbon versus nitrogen atoms of the heterocyclic cations has interesting stabilization and destabilization effects, respectively.     

Thermochemical properties of HxNO molecules and ions from ab initio electronic structure theory

Coupled-cluster calculations through noniterative triple excitations were used to compute optimized structures, atomization energies at 0 K, and heats of formation at 0 and 298 K for NH2O, HNOH, NH2O-, NH2OH+, NH3OH+, HNO-, and HON. These molecules are important in the gas-phase oxidation of NH3, as well as its solution-phase chemistry. The O-H, N-H, and N-O bond energies of these molecules are given and compared. The N-H and O-H bond energies are quite low, and, for NH2OH, the O-H bond is weaker than the N-H bond (by 7.5 kcal/mol). The energetics for a variety of ionic chemical processes in the gas phase, including the electron affinities of NH2O and HNO, the proton affinities of NH2O and NH2OH, and the acidities of NH2OH and NH2O, are given. The compounds are weak bases and weak acids in the gas phase. Solvation effects were included at the PCM and COSMO levels. The COSMO model gave better values than the PCM model. The relative values for pKa for NH2O and NH2OH are in good agreement with the experimental values, showing both compounds to be very strong bases in aqueous solution with NH2OH being the stronger base by 1.8 pK units at the COSMO level, compared to the experimental pK difference of 1.1+/-0.3 pK units. We predict that NH2OH+ will not be formed in aqueous solution, because it is a very strong acid. Based on the known acidity of NH3OH+, we predict pKa(NH2OH+)=-5.4 at the COSMO level, which is in good agreement with the experimental estimate of pKa(NH2OH+)=-7+/-2.     

Saturated nitrogen-containing heterocycles. VIII. Synthesis and properties of some substituted pyrrolidylalkanols

Phenyl-substituted pyrrolidylalkanols were synthesized by hydrogenation of the corresponding furan amines in acidic aqueous solution in the presence of nickel on diatomaceous earth. Terephthalates, carbamates, and other pyrrolidylalkanol derivatives were obtained. The ability of (2-pyrrolidyl)-3-alkanols to form an intramolecular hydrogen bond was studied by IR spectroscopy.See [1] for communication VII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 186–190, February, 1976.     

Heats of formation of organic molecules calculated from ab initio theory and a group equivalent scheme: Alkenes

A bond and group equivalent scheme that allows the calculation of heats of formation of alkenes from ab initio 6-31G* energies has been developed. For a group of 26 compounds, the root mean square (rms) error for the calculated heat of formation was 0.78 kcal/mol. Heats of formation have been predicted for an additional nine compounds for which the experimental values are either unknown or suspect. The heats of hydrogenation of barrelene and related compounds are discussed. © 1994 by John Wiley & Sons, Inc.     

Thermodynamic properties and aggregate formation of surfactant-like molecules from theory and simulation

The goal of this work is twofold: to predict the phase equilibria behavior of simplified surfactant models and to predict the population of aggregates as a function of pressure. We compare Monte Carlo simulation results of these systems with predictions from a modified version of the statistical associating fluid theory (soft-SAFT). Surfactant-like molecules are modeled as Lennard-Jones chains of tangent segments with one or two association sites. We study the influence of the number and location of the association sites on the thermodynamic properties and fraction of nonbonded molecules in all cases. The influence of the chain length is also investigated for a particular location of the sites. Results are compared with NPT Monte Carlo simulations to test the accuracy of the theory, and to study the molecular configurations of the system. Soft-SAFT is able to quantitatively predict the MC PVT results, independently of the location of the association sites. The theory is also able to capture the qualitative trend of the population of aggregates with pressure. Quantitative agreement is only obtained for specific locations of the sites.     

Heats of formation of krypton fluorides and stability predictions for KrF4 and KrF6 from high level electronic structure calculations

Atomization energies at 0 K and heats of formation at 0 and 298 K are predicted for KrF+, KrF-, KrF2, KrF3+, KrF4, KrF5+, and KrF6 from coupled-cluster theory (CCSD(T)) calculations with effective core potential correlation-consistent basis sets for krypton. To achieve near chemical accuracy (+/-1 kcal/mol), three corrections were added to the complete basis set binding energies based on frozen core coupled-cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, and a correction for first-order atomic spin-orbit effects. Vibrational zero point energies were computed at the coupled-cluster level of theory. The calculated value for the heat of formation of KrF2 is in excellent agreement with the experimental value. Contrary to the analogous xenon fluorides, KrF2, KrF4, and KrF6 are predicted to be thermodynamically unstable with respect to loss of F2. An analysis of the energetics of KrF4 and KrF6 with respect to fluorine atom loss together with calculations of the transition states for the intramolecular loss of F2 show that fluorine atom loss is the limiting factor determining the kinetic stabilities of these molecules. Whereas KrF4 possesses a marginal energy barrier of 10 kcal/mol toward fluorine atom loss and might be stable at moderately low temperatures, the corresponding barrier in KrF6 is only 0.9 kcal/mol, suggesting that it could exist only at very low temperatures. Although the simultaneous reactions of either two or four fluorine atoms with KrF2 to give KrF4 or KrF6, respectively, are exothermic, they do not represent feasible synthetic approaches because the attack of the fluorine ligands of KrF2 by the fluorine atoms, resulting in F2 abstraction, is thermodynamically favored over oxidative fluorination of the krypton central atom. Therefore, KrF6 could exist only at very low temperatures, and even the preparation of KrF4 will be extremely difficult.     

Saturated nitrogen-containing heterocycles. 18. Catalytic synthesis and formation mechanism of substitutedcis-decahydroquinolines and their isologues

Hydromethylamination of 1,3-diaryl-3-(2-oxocyclohexyl)propan-1-ones produces N-methyl-2,4-diaryldecahydroquinolines with cis-fused hetero- and carbocycles that are stabilized in the A conformation. The reaction involves ^2,3,9,10 intermediates and their subsequent reduction.For No. 17, see [1].N. G. Chernyshevskii, Saratov State University, Saratov 410026, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 929–933, July, 1999.     

Synthesis of nitrogen-containing heterocycles. 3. Formation and structure of new 1,2,4-triazole derivatives

Treatment of N(3)-[(2-cyano-2-ethoxycarbonyl)vinyl]amino-N(4),N(4)-dimethylaminomethylenehydrazones of aromatic carbonyl compounds with hot acetic acid resulted in the formation of symmetrical gem-bis-(3-dimethylamino-1,2,4-triazol-1-yl)methanes, (3-dimethylamino-1,2,4-triazol-1-yl)arylmethyl acetates, and (3-dimethylamino-1,2,4-triazol-1-yl)alkenes of a gem-diaryl type depending upon whether the carbonyl compound was aldehyde or ketone.     

Macrocycles,derivatives of nitrogen-containing heterocycles 2. Synthesis and electrochemical properties of diindolizinadiquinoxalinacyclooxaalkaphanes

Phenylindolizinylquinoxalinomonopodands, obtained by the reaction of 1-(phenylindolizin-2-yl)quinoxalin-2(1H)-one with corresponding dibromotrioxa- and dibromopentaoxaalkanes, undergo oxidative dehydrocyclization assisted by molecular iodine to yield new redox-active diindolizinadiquinoxalinacyclooxaalkaphanes. Using CVA, the indolizine fragments of the heterocyclophanes in acetonitrile are found to undergo three-step oxidation with transfer of one electron in each step. The first and the third steps are reversible, whereas the second is irreversible. The oxidation at potentials of the first peak leads to the stable radical cations registered by ESR (g = 2.0024, a _2N = 0.26 mT).     

Heats of formation of xenon fluorides and the fluxionality of XeF(6) from high level electronic structure calculations

Atomization energies at 0 K and heats of formation at 0 and 298 K are predicted for XeF(+), XeF(-), XeF(2), XeF(4), XeF(5)(-), and XeF(6) from coupled cluster theory (CCSD(T)) calculations with new correlation-consistent basis sets for Xe. To achieve near chemical accuracy (+/-1 kcal/mol), up to four corrections were added to the complete basis set binding energies based on frozen core coupled cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, a correction for first-order atomic spin-orbit effects, and in some cases, a second-order spin-orbit correction. Vibrational zero-point energies were computed at the coupled cluster level of theory. The structure of XeF(6) is difficult to obtain with the C(3)(v)() and O(h)() structures having essentially the same energy. The O(h)() structure is only 0.19 kcal/mol below the C(3)(v)() one at the CCSD(T)/CBS level using an approximate geometry for the C(3)(v)() structure. With an optimized C(3)(v)() geometry, the C(3)(v)() structure would probably become slightly lower in energy than the O(h)() one. The calculated heats of formation for the neutral XeF(n)() fluorides are less negative than the experimental values from the equilibrium measurements by 2.0, 7.7, and 12.2 kcal/mol for n = 2, 4, and 6, respectively. For the experimental values, derived from the photoionization measurements, this discrepancy becomes even larger, suggesting a need for a redetermination of the experimental values. Evidence is presented for the fluxionality of XeF(6) caused by the presence of a sterically active, free valence electron pair on Xe.     

Perturbation theory for excited states of molecules. I

The problem of perturbations of excited states is discussed and three methods are developed. The first of these uses a zero order wave-function made up of a linear sum of singly excited SCF configurations, whereas the second uses just one of these configurations. The third method is restricted to small -systems, the zero order wave-function being a linear sum of all possible determinants formed from the basis set used. The perturbations considered here are one-electron operators. Example calculations are performed on the butadiene molecule within the context of the -electron approximation.

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Zusammenfassung Für das Problem einer Störung von Einelektronen-Operatoren für angeregte Zustände werden drei Verfahren vorgeschlagen: Erstens die Verwendung einer Zustandsfunktion nullter Ordnung, die eine Linearkombination einfach angeregter SCF-Konfigurationen ist, zweitens die entsprechende Verwendung nur einer ausgewählten Konfiguration. Drittens läßt sich, wenn auch nur bei kleinen -Elektronensystemen, als nullte Näherung eine Linearkombination von allen möglichen angeregten Konfigurationen verwenden. Als Beispiel wird das -Elektronensystem des Butadiens gewählt.

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Résumé Discussion du problème de perturbation pour les états excités et développement de trois méthodes. La première utilise une fonction d'ordre zéro combinaison linéaire de configurations SCF monoexcitées, alors que la seconde utilise seulement une de ces configurations. La troisième méthode est restreinte à de petits systèmes , la fonction d'onde d'ordre zéro étant une combinaison linéaire de tous les déterminants construits dans la base utilisée. Les perturbations envisagées ici sont constituées par des opérateurs monoélectroniques. La molécule de butadiène sert d'exemple dans le cadre de l'approximation à électrons .

     

Azomethines of nitrogen-containing heterocycles. I. Synthesis and study of the structures of schiff bases from 3-methyl-2-azafluorenone and arylamines

In an investigation of the conditions for the formation of Schiff bases from 3-methyl-2-azafluorenone and arylamines it was shown that the use of boron trifluoride etherate as the catalyst insures the highest yields. The fundamental possibility of the preparation of Schiff bases by condensation of 3-methyl-2-azafluorene with p-nitrosodimethylaniline and subsequent reduction of the resulting oxazirane structure is demonstrated. The ratio of the cis and trans isomers of the resulting azomethines was established on the basis of PMR spectral data.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 109–115, January, 1976.     

Ensemble representable densities for atoms and molecules. I. General theory

A method to obtain ensemble representable densities from experimental diffraction data is proposed. The method uses ab initio molecular densities instead of the commonly employed one-electron orbital densities, and as a result, few parameters need to be optimized in the fitting procedure to the experimental structure factors. The optimized coefficients can provide information about intra- and intermolecular electronic correlations, spin-orbit coupling, etc. This work also provides new explicit formulas to determine the rank of a fermionic wave function, i.e., the rank of the one-fermion density matrix. © 1995 John Wiley & Sons, Inc.     

The response of electronic and energetic properties of conjugated vs aromatic molecules to an external uniform electric field

The susceptibility of electric and energetic properties of two sets of molecules to perturbation in a uniform electric field was investigated. The molecules of one set were deca-1,3,5,7-pentaene terminated with two functional groups, R₁ and R₂; those of the second set were 4-R₁-4′-R₂-p-diphenylbenzenes, with R₁ and R₂ being the same as in the polyene set. The polyene and aromatic molecules had similar lengths of the system of conjugated bonds between the two most extreme carbon atoms. Dipole moments were used as determinants of the overall charge transfer within the molecules. The electric field was directed along the main (longest) axes of the molecules from the negative pole to the positive. Comparison of the effect of the charge relocation in both sets of conjugated molecules revealed that the charge transfer imposed by the electric field was more efficient in the polyenes than in the aromatic compounds; however, for the molecule pairs with the same R₁ and R₂, reversal of the dipole moment direction falls at the same field strength. Parabolic dependence of the molecules’ energy as a function of field strength can also be interpreted in terms of the response of electron density to an electric field.

     

Variational method for the calculation of the vibrational structure of the electronic spectra of polyatomic molecules. I

A method is proposed to calculate the vibrational structures of the electronic spectra of polyatomic molecules based on the variational solution of the vibrational problem in the excited state with the vibrational wave functions of the ground state as basis set. The electrono-vibrational problem leads to an evaluated and diagonalized variational matrix. The elements of the variational matrix have a simple form which is easily evaluated, has a clear physical meaning and is directly interconnected with observed spectral effects. This allows preliminary estimation of spectral phenomena and correction of the molecular model to take account of experimental results. The use of contemporary methods of diagonalization of the variational matrix, which possesses a characteristic structure, facilitates a tenfold increase in the speed of the method in comparison with traditional methods.K. A. Timiryazev Agricultural Academy. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 141–148, January–February, 1993.     

A perspective on the electronic structure calculations for properties of battery electrode materials

Electronic structure calculations are widely and increasingly utilized for understanding, designing, screening, and analyzing the material properties in various applications. Especially, for the last two decades, researches on the rechargeable battery have grown rapidly with the help of computational materials science. In this perspective, we briefly overview the current status of such progresses in the battery electrode. In particular, the configuration problem to determine the ground structure for estimating thermodynamic properties such as voltage and intermediate phase is discussed, followed by theoretical interpretations on the phase behavior and phase boundary migration. Some future challenges are commented. © 2015 Wiley Periodicals, Inc.     

Prediction of the formation and stabilities of energetic salts and ionic liquids based on ab initio electronic structure calculations

A computational approach to predict the thermodynamics for forming a variety of imidazolium-based salts and ionic liquids from typical starting materials is described. The gas-phase proton and methyl cation acidities of several protonating and methylating agents, as well as the proton and methyl cation affinities of many important methyl-, nitro-, and cyano-substituted imidazoles, have been calculated reliably by using the computationally feasible DFT (B3LYP) and MP2 (extrapolated to the complete basis set limit) methods. These accurately calculated proton and methyl cation affinities of neutrals and anions are used in conjunction with an empirical approach based on molecular volumes to estimate the lattice enthalpies and entropies of ionic liquids, organic solids, and organic liquids. These quantities were used to construct a thermodynamic cycle for salt formation to reliably predict the ability to synthesize a variety of salts including ones with potentially high energetic densities. An adjustment of the gas phase thermodynamic cycle to account for solid- and liquid-phase chemistries provides the best overall assessment of salt formation and stability. This has been applied to imidazoles (the cation to be formed) with alkyl, nitro, and cyano substituents. The proton and methyl cation donors studied were as follows: HCl, HBr, HI, (HO)2SO2, HSO3CF3 (TfOH), and HSO3(C6H4)CH3 (TsOH); CH3Cl, CH3Br, CH3I, (CH3O)2SO2, CH3SO3CF3 (TfOCH3), and CH3SO3(C6H4)CH3 (TsOCH3). As substitution of the cation with electron-withdrawing groups increases, the triflate reagents appear to be the best overall choice as protonating and methylating agents. Even stronger alkylating agents should be considered to enhance the chances of synthetic success. When using the enthalpies of reaction for the gas-phase reactants (eq 6) to form a salt, a cutoff value of -13 kcal mol(-1) or lower (more negative) should be used as the minimum value for predicting whether a salt can be synthesized.     

A principle of linear covariance for quantum mechanics and the electronic structure theory of molecules and other atom clusters

Quantum mechanical equations should look the same in any non-orthonormal or orthonormal basis frame when properly formulated so as to be fully covariant under the largest group indicated. Non-orthonormal frames are crucial especially for the quantum theory of chemistry. Various methods such as valence-bond, localized orbital, molecular orbital, etc. result from a single formulation using the principle of linear covariance which is stated, proved, and exemplified. Molecular quantities with the full inclusion of overlaps are derived with the same ease as without overlaps.