17th IUPAC Conference on Chemical Thermodynamics will be held July 28–August 2, 2002 in Rostock,Germany http://icct.chemie.uni-rostock.de

Journal of Thermal Analysis and Calorimetry -     

Chemical characterization of gallium droplets grown by LP-MOCVD

This study is concerned with the chemical characterization of metallic gallium droplets, obtained on silicon (1 0 0) substrates with a single growth step, by the LP-MOCVD technique with TMGa like precursor. These structures are characterized by SIMS, XPS and TEM. The analyses results lead to a structure proposition for the droplets. The core is composed of metastable metallic gallium with a non-negligible carbon quantity probably coming from incomplete precursor decomposition. The outer part, composed of gallium oxide maintains the structure stability. Covering of the substrate by a thin gallium layer of gallium compounds is observed.     

Erkennung von Rubidium neben Caesium

Ohne Zusammenfassung     

Bestimmung der Salpeters?ure in Wismuthverbindungen

Ohne Zusammenfassung     

Comprehensive experimental and theoretical study of chemical equilibria in the reacting system of the tert-amyl methyl ether synthesis

The chemical equilibrium of the reactive system (methanol+isoamylenes<-->methyl tert-amyl ether) was studied in the temperature range 298-393 K in the liquid phase using the method of sealed ampoules as well as in the gaseous phase using a tubular flow reactor in the temperature range 355-378 K. In both cases, a cation exchanger Amberlist-15 was used as a heterogeneous catalyst. The reactive system of the methyl tert-amyl ether synthesis exhibits a strong nonideal behavior of the mixture compounds in the liquid phase. The knowledge of the activity coefficients is required in order to obtain the thermodynamic equilibrium constants Ka. Two well-established procedures, UNIFAC and COSMO-RS, have been used to assess activity coefficients of the reaction participants in the liquid phase. Thermodynamic equilibrium constants KP measured in the gaseous phase together with the vapor pressures of the pure compounds have been used to obtain Ka in the liquid phase on a consistent experimental basis in order to check the results obtained from the UNIFAC and COSMO-RS methods. Enthalpies of reactions DeltarH degrees of the methyl tert-amyl ether synthesis reaction in the gaseous and in the liquid phase were obtained from temperature dependences of the corresponding thermodynamic equilibrium constants. Consistency of the experimental data of DeltarH degrees was verified with help of enthalpies of formation and enthalpies of vaporization of methyl tert-amyl ether, methanol, and methyl-butenes, available from the literature. For the sake of comparison, high-level ab initio calculations of the reaction participants have been performed using the Gaussian-03 program package. Absolute electronic energy values, normal frequencies (harmonic approximation), and moments of inertia of the molecules have been obtained using G2(MP2), G3(MP2), and G3 levels. Using these results, calculated equilibrium constants and the enthalpy of reaction of the methyl tert-amyl ether synthesis in the gaseous phase based on the principles of statistical thermodynamics are found to be in acceptable agreement with the data obtained from the thermochemical measurements.     

Pairwise-substitution effects and intramolecular hydrogen bonds in nitrophenols and methylnitrophenols. Thermochemical measurements and ab initio calculations

The standard molar enthalpies of formation in the gaseous state of a series of nitrophenols, 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 5-methyl-2-nitrophenol, 2-methyl-5-nitrophenol, and 3-methyl-4-nitrophenol, have been obtained from combustion calorimetry and results from the temperature dependence of the vapor pressure measured by the transpiration method. To verify the experimental data, ab initio calculations of all compounds have been performed using MP, DFT, and G3 methods. Enthalpies of formation derived from the G3 methods are in a good agreement with the experimental results. The quantitative analysis of ortho, meta, and para pairwise-substituent effects in nitrophenols has been performed, and the strength of intramolecular hydrogen bonding in o-nitrophenol has been derived from thermochemical results and compared with those obtained from spectroscopic experiments and ab initio calculations. The new results help to resolve uncertainties in the available thermochemical data on extended series of nitrophenols.     

Hopfen

Ohne Zusammenfassung