Calculation of the thermodynamic characteristics of ions in vapor over sodium fluoride

The geometric parameters, normal vibration frequencies, and thermochemical characteristics of the ions present in vapor over sodium fluoride, Na₂F⁺, Na₃F ₂ ⁺ , NaF ₂ ^? , and Na₂F ₃ ^? , were calculated ab initio by the Hartree-Fock method and taking into account electron correlation. The main equilibrium configuration of all ions was found to be the linear configuration of D _∞h symmetry. Pentaatomic ions could also exist as two isomers, planar cyclic of C _2v symmetry and bipyramidal of D _3h symmetry. Their energies were higher than that of the D _∞h isomers, and their contents in vapor were negligibly low. The energies and enthalpies of dissociation of the ions with the elimination of the NaF molecule were calculated. The enthalpies of formation of the ions were obtained.     

Energy barriers to gas-phase unimolecular decomposition of trinitrotoluenes

Alternative versions of gas-phase unimolecular decomposition of six isomeric trinitrotoluenes, in particular homolytic dissociation of C_arom–NO₂ and C_arom–CH₃ bonds, nitro–nitrite rearrangement, intramolecular hydrogen transfer from the methyl group to nitro group with formation of aci-trinitrotoluenes, and formation of various bicyclic intermediates, have been simulated at the B3LYP/6-31+G(2df,p) level of theory. Except for 3,4,5-trinitrotoluene, the most energetically favorable for all other examined trinitrotoluenes is intramolecular hydrogen transfer. 3,4,5-Trinitrotoluene preferentially decomposes via formation of [6 + 4]-bicyclic intermediates or homolytic dissociation of the C_arom–NO₂ bond.     

Die thermische Zersetzung von Bariumazid-Einkristallen, 5. Mitt.: Der Einfluß der Korngröße auf die thermische Zersetzung von Bariumazid

Decomposition studies on ground samples of anhydrous Ba(N₃)₂ with defined particle size are described. The kinetic equations derived for single crystals hold for the decomposition of powders too. The far faster decomposition of powders is caused both by the increased numberN ₀ of potential nuclei forming sites and the larger specific surfaceF ₀/V ₀, whereas the rate constantsk ₁ andk ₂ for nucleation and linear nucleus growth, resp., and their respective activation energies coincide with the data for single crystals. The proportionality between the rate of decomposition and the specific surface is confirmed experimentally and thereby a further proof of the geometric decomposition model is established. Independent of particle size and temperture always 75% of the azide are transformed into nitride during thermal decomposition, this value corresponding exactly to the theoretical one. It is shown experimentally that with decomposition conditions no reaction takes place between metallic Ba and N₂ in its electronic ground state and therefore the mechanism proposed for nitride formation is confirmed.     

Heat properties of Bu<Subscript>4</Subscript>NBr solutions in binary mixtures based on formamide

Heat effects of tetrabutylammonium bromide dissolution in mixtures of formamide with methanol and ethylene glycol at 25°C were determined. Partial molar enthalpies of the components of formamide-ethylene glycol mixtures at 25°C were measured by the calorimetric method, and the mixing enthalpies of this system were determined. Within the limits of the second approximation of the Debye-Hueckel theory the standard enthalpies of dissolution Δ_dis H ⁰ were calculated, and the enthalpies of Bu₄NBr transfer from formamide in its mixtures with water methanol and ethylene glycol were found on this basis. The enthalpy parameters of Bu₄NBr pair interactions with the components of the formamide-water, formamide-methanol, and formamide-ethylene glycol mixtures were calculated. The results obtained were compared with the data for the systems containing N-methylformamide and N,N-dimethylformamide.     

Energy barriers to gas-phase unimolecular decomposition of mono- and dinitrotoluenes

Alternative paths of gas-phase unimolecular decomposition of three nitrotoluenes and six dinitrotoluenes, in particular homolytic dissociation of the C–N bond, nitro–nitrite rearrangement, intramolecular hydrogen transfer from the methyl to nitro group with formation of isomeric aci-nitrotoluenes, and various paths involving formation of bicyclic intermediates, have been studied at the DFT B3LYP/6-31+G(2df,p) level of theory using GAUSSIAN 09 software package. The most energetically favorable path for o-nitrotoluene and 2,3-, 2,4-, 2,5-, and 2,6-dinitrotoluenes is the formation of aci-nitrotoluenes. The effect of the substrate structure on the competition between different mechanisms of these reactions has been analyzed.     

A Systematic Search for Structures and Stabilities of Asymmetric Clusters (HfInN<Subscript>3</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 1-6)

In order to find single source precursors (SSP), the structures, relative stabilities, and IR spectra of small asymmetric clusters (HFInN₃) _n (n = 1–6) are systematically investigated by means of the density functional theory at the B3LYP level. The obtained geometries show that the frameworks of clusters (HFInN₃) _n (n = 2–6) prefer to be 2n-membered ring with alternating indium and α-nitrogen atoms. The averaged binding energies reveal that all of asymmetric clusters (HFInN₃) _n (n = 1–6) can continue to gain energy as the cluster size n increasing. The second-order difference of energy (Δ₂E) and the HOMO-LUMO energy gap (E_gap) as a function of the cluster size n both exhibit a pronounced even-odd alternation phenomenon. The influences of cluster size n and temperature T on the thermodynamic properties of clusters are discussed. Judged by enthalpies and Gibbs free energies, the formations of the most stable clusters (HFInN₃) _n (n = 2–6) from the monomer are thermodynamically favorable in the range of 200–800 K.     

Determination of combustion energies and the standard enthalpies of formation for the complexes of RE(Et<Subscript>2</Subscript>dtc)<Subscript>3</Subscript>(phen)

Solid complexes, RE(Et₂dtc)₃(phen) (RE=La, Pr, Nd, Sm—Lu), were synthesized with sodium diethyldithiocarbamate (NaEt₂dtc3H₂O), 1,10-phenanthroline (o-phen?H₂O) and hydrated lanthanide chlorides in absolute ethanol. The constant-volume combustion energies of complexes, Δ _C U, were determined by a precise rotating-bomb calorimeter at 298.15 K. The standard enthalpies of combustion, Δ_CH_m ^θ, and standard enthalpies of formation, Δ_fH_m ^θ, were calculated for these complexes, respectively. The experiment results showed the “tripartite effect” of rare earth.     

<Emphasis Type="Italic">Ab initio</Emphasis> study of scandium fluoride molecules: ScF,ScF<Subscript>2</Subscript>, AND ScF<Subscript>3</Subscript>

Equilibrium geometric parameters, normal mode frequencies and intensities in IR spectra, atomization enthalpy, and relative energies of low-lying electronic states of scandium fluoride molecules (ScF, ScF₂, and ScF₃) are calculated by the coupled-cluster method (CCSD(T)) in triple-, quadruple, and quintuple-zeta basis sets with the subsequent extrapolation of the calculation results to the complete basis set limit. The ScF molecule is also studied by the CCSDT technique. The error in the approximate calculation of triple excitations in the CCSD(T) method does not exceed 0.002 Å for the equilibrium internuclear distance R _e, 4 cm^?1 for the vibrational frequency, and 0.2 kcal/mol for the dissociation energy of the molecule. In the ground electronic state \(\tilde X^2 \) A ₁(C _2ν ) of ScF₂ molecules, R _e(Sc-F) = 1.827 Å and α_e(F-Sc-F) = 124.2°; the energy barrier to bending (linearization) h = E _min(D _g8h ) ? E _min(C_2ν) = 1652 cm^?1. The relative energies of Ã²Δ _g and \(\tilde B^2 \)Π _g electronic states are 3522 cm^?1 and 14633 cm^?1 respectively. The bond distance in the ScF₃ molecule (\(\tilde X^1 \) A′₁, D _3h ) is refined: R _e(Sc-F) = 1.842 Å. The atomization enthalpies Δ_at H ₂₉₈ ⁰ of ScF _k molecules are 139.9 kcal/mol, 289.0 kcal/mol, and 444.8 kcal/mol for k = 1, 2, 3 respectively.     

Effect of the structure of cyclic <Emphasis Type="Italic">N</Emphasis>-nitramines on the rate and mechanism of their thermolysis

Manometry together IR spectroscopy, mass spectrometry, and chromatography were used to study thermolysis of six-membered cyclic N-nitramines containing one, two, or three nitramine fragments, as well as oxo, gem-dinitro, azide, nitroimino, amino, and tetrazolyl functions. An effect of the conformation and functional groups on the rate, mechanism, and activation parameters of the limiting stage of themolysis was revealed.     

Thermodynamics of vaporization of the mixed-ligand complex of sodium dipivaloylmethanate with <Emphasis Type="Italic">o</Emphasis>-phenanthroline Na(thd)(phen)

Vaporization of the complex between sodium dipivaloylmethanate and o-phenanthroline Na(thd)(phen) is studied using the Knudsen effusion method and mass spectral analysis of the gas-phase composition. Sublimation of the compound is found to occur congruently. Saturated vapor predominantly consists of o-phenanthroline molecules C₁₂H₈N₂, trimeric molecules Na₃(thd)₃, and a minor amount of Na₄(thd)₄ and Na(thd)(phen) molecules. The absolute partial pressures and enthalpies of sublimation of the gas-phase components, as well as the Δ_fG⁰(T) of formation of the complex from Na(thd)(s) and Phen(l), are calculated. The standard enthalpy of dissociation of gaseous Na(thd)(phen) into Na₃(thd)₃(g) and Phen(g) is estimated.     

The thermodynamic characteristics of vaporization in the NaI-PrI<Subscript>3</Subscript> system

The vaporization of the NaI-PrI₃ quasi-binary system was studied by high-temperature mass spectrometry over the whole concentration range. At 623–994 K, saturated vapor contained not only (NaI) _n and (PrI₃) _n molecules (n = 1, 2) and Na⁺(NaI) _n (n = 0–4) and I^?(PrI₃) _n (n = 1–2) ions but also mixed molecular and ionic associates recorded for the first time (NaPrI₄, Na₂PrI₅, NaPrI ₃ ⁺ , Na₂PrI ₄ ⁺ , Na₃PrI ₅ ⁺ , Na₄PrI ₆ ⁺ , NaPrI ₅ ^? , and NaPr₂I ₈ ^? ). The partial vapor pressures of molecules were calculated, and the equilibrium constants of the dissociation of neutral and charged associates were measured. The enthalpies of molecular and ion-molecular reactions were determined, and the enthalpies of formation of gaseous molecules and ions were obtained.     

Standard Enthalpies of Formation of <Emphasis Type="Italic">N</Emphasis>-Methylglycine and Products of Its Dissociation in Aqueous Solutions

Enthalpies of dissolution of crystalline N-methylglycine in water and in aqueous potassium hydroxide solutions are determined at 298.15 K via direct calorimetry. Standard enthalpies of formation of the amino acid and products of its dissociation in aqueous solution are calculated.     

Reaction of transsilylation of <Emphasis Type="Italic">N</Emphasis>-methyl-<Emphasis Type="Italic">N</Emphasis>-trimethylsilylacetamide with silanes ClCH<Subscript>2</Subscript>SiR<Superscript>1</Superscript>R<Superscript>2</Superscript>Cl

The reaction of N-methyl-N-trimethylsilylacetamide with silanes ClCH₂SiR¹R²Cl (R¹, R² = H, Me; H, Ph; Ph₂) leads to the formation of (O→Si) chelate compounds with pentacoordinate silicon: N-[chloro(methyl)-silyl]methyl-, N-[chloro(phenyl)silyl]methyl-, and N-[chloro(diphenyl)silyl]methyl-N-methylacetamides. From the data of multinuclear NMR spectroscopy, the intermediates of the reaction of N-methyl-N-trimethylsilylacetamide with ClCH₂SiPhHCl and ClCH₂SiPh²Cl are stable in CDCl₃ solution at room temperature during several days and slowly rearrange to the final (O–Si) chelate compounds.     

Thermochemical analysis of intermolecular interactions between <Emphasis Type="Italic">N</Emphasis>-acetylglycine and polyols in aqueous solutions

The integral enthalpies of dissolution Δ_sol H _m for N-acetylglycine in aqueous solutions of glycerol, ethylene glycol and 1,2-propylene glycol are measured via solution calorimetry. The standard enthalpies of dissolution (Δ_sol Н ⁰) and transfer (Δ_tr Н ⁰) for N-acetylglycine from water to aqueous solutions of polyhydric alcohols are calculated from experimental data. Positive values of enthalpy coefficients of pair interactions h _xy for amino acids and polyol molecules are calculated using the McMillan–Mayer theory. The results are discussed using an approach for evaluating different types of interactions in ternary systems and the effect the structural features of interacting biomolecules have on the thermochemical characteristics of N-acetylglycine dissolution.     

Thermooxidative decomposition of heterocyclic <Emphasis Type="Italic">N</Emphasis>-oxides

Thermooxidative decomposition of pyridine N-oxide, 4-(4-dimethylaminostyryl)pyridine N-oxide, 4-(4-methoxystyryl)pyridine N-oxide, quinoline N-oxide, 2-methylquinoline N-oxide, 4-chloroquinoline N-oxide, 2-styrylquinoline N-oxide, and 2-(4-dimethylaminostyryl)quinoline N-oxide was studied. The kinetic parameters of the thermooxidative processes were calculated according to three independent procedures. The relation between the nature of heterocyclic N-oxide and its stability to thermal oxidation was analyzed.     

Thermodynamic characteristics of complexation between Ho<Superscript>3+</Superscript> and ethylenediamine-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>'-disuccinic acid in aqueous solutions at 298.15 K

The thermodynamic characteristics of complexation between ethylenediamine-N,N'-disuccinic acid (H₄Y; EDDA) and Ho³⁺ ion were determined calorimetrically and potentiometrically at 298.15 K and ionic strengths of 0.1, 0.5, 1.0, and 1.5 (KNO₃). The logK, Δ_rG, Δ_rH, and Δ_rS values for the formation of HoY^– and HOHY complexes were calculated at the studied and zero ionic strength values. The changes in thermodynamic parameters of the reactions are discussed.     

Enthalpies of Dissolution of Crystalline Naproxen Sodium in Water and Potassium Hydroxide Aqueous Solutions at 298 K

The enthalpies of dissolution of crystalline naproxen sodium in water and aqueous solutions of KOH at 298.15 K are measured by direct calorimetric means in a wide range of concentrations. The acid–base properties of naproxen sodium at ionic strength I ~ 0 and I = 0.1 (KNO₃) and a temperature of 298.15 K are studied by spectrophotometric means. The concentration and thermodynamic dissociation constants are determined. The standard enthalpies of the formation of naproxen sodium and the products of its dissociation in aqueous solution are calculated.     

The standard thermodynamic properties of 4<Emphasis Type="Italic">f</Emphasis> metal trichlorides

The enthalpies of sublimation Δ_sub H ⁰(298) of 4f metal trichlorides were calculated by the second and third laws of thermodynamics from saturated vapor pressures using the thermodynamic functions of the condensed and gaseous states suggested by us. The set of the Δ_sub H ^o(298) enthalpies was analyzed to determine the most reliable values. The enthalpies of atomization found from these values were compared with those calculated from the measured equilibrium constants of gas phase reactions with the participation of the compounds under consideration and the enthalpies of atomization found from the experimental appearance potentials AP(Ln⁺/LnCl₃). Recommended Δ_at H ^o(298) values were obtained for all the 4f metal trichlorides.     

Reactions of arylsulfinyl chlorides and <Emphasis Type="Italic">N</Emphasis>-(arylsulfonyl)arylsulfinimidoyl chlorides with <Emphasis Type="Italic">p</Emphasis>-aminophenols

In reactions of arylsulfinyl chlorides and N-(arylsulfonyl)arylsulfinimidoyl chlorides with p-aminophenols formed N-arylthio-1,4-benzoquinone imines, evidently through a stage of N-arylsulfinyl-4-aminophenols and N-(N-arylsulfonyl)arylsulfinylimidoyl-4-aminophenols that under the reaction conditions eliminate respectively H₂O and ArSO₂NH₂.     

Alkylation of 2-(methylsulfanyl)-6-polyfluoroalkylpyrimidin-4(3<Emphasis Type="Italic">H</Emphasis>)-ones with haloalkanes

The alkylation of ambident anions of 2-(methylsulfanyl)-6-(polyfluoroalkyl)pyrimidin-4(3H)-ones with 4-bromobutyl acetate leads to concurrent formation of O- and N-(4-acetoxybutyl) derivatives. Polar aprotic solvents favor formation of the O-isomer, and weakly polar dioxane favors N-alkylation. The reaction of 2-(methylsulfanyl)-6-(trifluoromethyl)pyrimidin-4(3H)-one with an equimolar amount of 1,2-dibromoethane in polar acetonitrile gives a mixture of N,N-, O,O-, and N,O-bridged bis-pyrimidines, as well as N- and O-[2-(methylsulfanyl)ethyl] derivatives, whereas in the presence of 10 equiv of 1,2-dibromoethane the N,O-isomer is formed as the only product. The reaction in weakly polar tetrahydrofuran yields N,N- and N,O-bispyrimidines.