Structural and thermodynamic aspects of electron diffraction by lithium fluoride dimers

Ivanovo Chemical Engineering Institute. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 1, pp. 60–67, January–February, 1991.     

A gas-phase electron-diffraction study of trvinylborane

Trivinylborane has been studied by standard electron-diffraction techniques. The best agreement with experiment is obtained with a planar dynamic model in which steric strain within the molecule is reduced by distortion of the vinyl groups, and shrinkages simulate considerable torsional motion about the B-C bonds. The following parameters (r_a basis) and e.s.d. were obtained: C-H = 1.092± 0.003 Å; C-C = 1.370 ± 0.006 Å; B-C = 1.558± 0.003 Å; ∠BCH = 116.5 ± 0.9 °; ∠BCC = 122.4 ± 0.9°; ∠CCH (trans to B) = 124.0 ± 1.6°; ∠CCH (cis to B) = 132.2 ± 2.3°. A static non-planar model has also been considered.The probable planarity of the molecule and the length of the C C bond are interpreted as evidence for π-electron delocalisation from carbon to boron.     

Kinetics of saturated water vapor sorption on soot particles

In order to study the condensation activity of carbon-containing aerosols, the kinetics of sorption of saturated water vapors was investigated on model soot samples modified by the deposition of organic and inorganic substances corresponding to different classes of compounds contained in solid state products of natural fuel combustion. The values of limiting water sorption were determined and rate constants were calculated. It was established that the limiting sorption on graphitized thermal soot (GTS) modified by acids and salts (e.g., phenol, benzoic, phthalic, trimellitic, and sulfuric acids; sodium benzoate; and ammonium sulfate) per modifier molecule rose by two orders of magnitude, relative to the initial carbon matrix, and ranged from ≈2 to 200 molecules. It was found that hydrophilic centers covalently bound to the surface of furnace black (FB) and its oxidized form are shielded to a considerable degree as a result of modification by hydrophobic substances (hexadecane, octacosane, anthracene, and stearic acid). We conclude that hexadecane modification of GTS containing hydrophilic centers not bound to its surface (sulfuric acid and ammonium sulfate molecules) have no effect on the sorption of saturated water vapors.     

Composition of saturated vapor over Ytterbium bromides

The vaporization process of ytterbium di- and tribromide was studied using high-temperature mass spectrometry over the temperature range of 850 to 1300 K. It was ascertained that, at the early vaporization stages, the vapor contained molecules YbBr₃, YbBr₂, YbBr, Br₂, Yb₂Br₂, Yb₂Br₃, Yb₂Br₄, Yb₂Br₅, Yb₂Br₆, and atoms Yb and Br. The partial pressures of all components of saturated vapor were calculated. It was found that vapor composition reflected the course of the reactions of decomposition of tribromide and disproportionation of dibromide in the condensed phase. It was concluded that vaporization of di- and tribromide was incongruent at the initial stages; vaporization of both agents acquired a congruent character with the Yb: Br = 1.0: 1.9_±0.2 ratio with time.     

Water dimer equilibrium constant of saturated vapor

The value and temperature dependence of the dimerization constant for saturated water vapor are determined. A general expression that links the second virial coefficient and the dimerization constant is obtained. It is shown that the attraction between water monomers and dimers is fundamental, especially at T > 350 K. The range of application for the obtained results is determined.     

Structural and thermodynamic aspects of ionic solvation in concentrated aqueous poly(ethylene glycol)

Solvation of ions in concentrated aqueous poly(ethylene glycol) (PEG) has been studied from thermodynamic and structural viewpoints using ion-transfer voltammetry at the interface between aqueous and nitrobenzene phases and X-ray absorption fine structure (XAFS). Systematic changes in the ion-transfer potential from water to aqueous PEG have been confirmed for several ions relative to the corresponding potential of tetraethylammonium ion (Et4N+), which is almost independent of PEG concentration. The results obtained for alkali cations strongly suggest the involvement of their complexation with PEG even in relatively diluted PEG solutions. It has been implied that the solvation circumstances of Br- and ClO4- are drastically altered when the PEG concentration becomes higher than particular critical values (e.g., 30-50% PEG200), where free water molecules are diminished because of the hydration of PEG. XAFS measurements have also been performed for K+ and Br- to get direct evidence for these findings. Although the spectra at the K K-edge clearly indicate the presence of a PEG complex of K+ in relatively diluted PEG solutions ( approximately 33% PEG200), an obvious increase in its ion-transfer potential has been detected at lower PEG concentrations, indicating that complexes formed at the interface rather than in bulk solution are transferred into an organic phase. Br- is fully hydrated in 0-50% PEG solutions, whereas some water molecules are replaced by PEG when the PEG concentration increases. Increasing the PEG concentration causes decreases in the coordination number from 6 in water to 2-3 in neat PEG. Thus, the present approach not only has elucidated the structural and thermodynamic aspects of ionic solvation in aqueous PEG but also has provided the information of the hydration of PEG.     

Heat capacity and cluster structure of saturated water vapor

The value and temperature dependence of the heat capacity of saturated water vapor are studied. It is shown that the behavior of the heat capacity is determined by the formation of dimers, tetramers, and higher-order clusters, and by excitation of the hydrogen bond vibrations within these clusters. The temperature regions that correspond to water vapor as (a) a mixture of monomers and dimmers and (b) as a mixture of monomers, dimmers, and tetramers, are determined.     

The viscosity of triethylamine vapor at low densities and in the saturated vapor phase

For the first time, results of high-precision measurements of the viscosity coefficient of triethylamine vapor at low densities are reported. The relative measurements with an all-quartz oscillating-disk viscometer were carried out along seven isochores at densities from 0.002 to 0.009 mol m⁻³ in the temperature range between 298 and 498 K. The uncertainty is estimated to be ±$\pm$0.2% at ambient temperature, increasing up to ±$\pm$0.3% at higher temperatures. First isothermal values were recalculated from the original experimental data and then evaluated with a first-order expansion for the viscosity, in terms of density. In addition, viscosity values of the saturated vapor were determined at low temperatures. The results are utilized to model the viscosity coefficient of triethylamine vapor at moderately low densities. A so-called individual correlation on the basis of the extended theorem of corresponding states was employed to describe the zero-density viscosity coefficient, whereas the Rainwater–Friend theory was used to represent the initial density dependence expressed as second viscosity virial coefficient.     

Synthesis and thermodynamic and structural characteristics of thallium(I) pivalate

Thallium pivalate was first synthesized and studied by mass spectrometry. It was shown that the set of characteristics makes thallium pivalate suitable as a precursor for the CVD preparation of oxide films and oxide materials.     

Interaction of indium antimonide with saturated sulfur vapor

The chemical reaction of single-crystal indium antimonide with saturated elemental sulfur vapor is diffusion-limited and leads to the formation of the triple layer In₂S₃–(xIn₂S₃ + (1–x)Sb₂S₃)–Sb on the surface of the samples. A model explaining the experimental facts is proposed.     

Structural and thermodynamic characterization of polyphenylbenzenes

The thermodynamic and structural study of a series of polyphenylbenzenes, from benzene, n(Ph) = 0, to hexaphenylbenzene, n(Ph) = 6, is presented. The available literature data for this group of compounds was extended by the determination of the relevant thermodynamic properties for 1,2,4-triphenylbenzene, 1,2,4,5-tetraphenylbenzene, and hexaphenylbenzene, as well as structural determination by X-ray crystallography for some of the studied compounds. Gas phase energetics in this class of compounds was analyzed from the derived standard molar enthalpies of formation in the gaseous phase. The torsional profiles relative to the phenyl-phenyl hindered rotations in some selected polyphenylbenzenes, as well as the gas phase structures and energetics, were derived from quantum chemical calculations. In the ideal gas phase, a significant enthalpic destabilization was observed in hexaphenylbenzene relative to the other polyphenylbenzenes, due to steric crowding between the six phenyl substituents. A relatively low enthalpy of sublimation was observed for hexaphenylbenzene, in agreement with the decreased surface area able to establish intermolecular interactions. The apparently anomalous low entropy of sublimation observed for hexaphenylbenzene is explained by its high molecular symmetry and the six highly hindered phenyl internal rotations. For the series of polyphenylbenzenes considered, it was shown that the differentiation in the entropy of sublimation can be chiefly ascribed to the torsional freedom of the phenyl substituents in the gas phase and the entropy terms related with molecular symmetry.     

Kinetic and thermodynamic aspects of miniemulsion copolymerization

Miniemulsion polymerization involves initiation of polymerization in preformed stable monomer emulsion droplets with average droplet diameter of 50–500 nm. At the end of the polymerization, only a fraction of the initial number of monomer droplets become polymer particles. The emulsifier system used for the preparation of such emulsions comprises a mixture of ionic surfactant and a fatty alcohol or long chain alkane (termed cosurfactant). The cosurfactant is essential for the formation of stable emulsion droplets and in addition it plays an important role in the interparticle monomer transport. Kinetic results are presented on conventional emulsion and miniemulsion copolymerization of different pairs of monomers, showing the main differences for both processes. These differences were related to the particle formation mechanism and the influence of the cosurfactant in the miniemulsion process. A theoretical model was developed, based on mass balances and equilibrium thermodynamics, which was found to describe accurately the experimentally generated data on comonomer distribution during the course of the copolymerization process and the interdroplet mass transport process.