Publications

Abstract The standard (p(o) = 0.1 MPa) molar energies of combustion in oxygen. at T = 298.15 K, of 5, 6- and 7-methoxy-alpha-tetralone were measured by static bomb calorimetry. The values of the standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry and corrected to T = 298.15 K. Combining these results, the standard molar enthalpies of formation of the compounds, in the gas phase, at T = 298.15 K, have been calculated, 5-methoxy-alpha-tetralone-(244.8 +/- 1.9) kJ . mol(-1), 6- methoxy-alpha-tetralone -(243.0 +/- 2.8) kJ . mol(-1) and 7-methoxy-alpha-tetralone -(242.3 +/- 2.6) kJ . mol(-1). Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets and more accurate correlated computational techniques of the MCCM/3 suite have been performed for the compounds. The agreement between experiment and theory gives confidence to estimate the enthalpy of formation of 8-methoxy-alpha-tetralone. Similar calculations were done for the 5, 6-, 7- and 8-methoxy-beta-tetralone, for which experimental work was not done. (C) 2008 Published by Elsevier Ltd.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation in the condensed state of chromanone, dihydrocoumarin, and 3-isochromanone were derived from the standard molar energies of combustion in oxygen at T = 298.15 K, measured by combustion calorimetry. Calvet microcalorimetry was used to derive the standard molar enthalpies of sublimation and vaporization. [GRAPHICS] From these values the standard molar enthalpies in the gaseous phase, at T = 298.15 K. were derived. Additionally estimates were performed of the enthalpies of formation of all the studied compounds in gas-phase, using DFT and other more accurate correlated calculations, together with appropriate isodesmic or homodesmic reactions. There is a reasonable agreement between computational and experimental results.

Abstract In this work, we have determined the experimental standard (p degrees = 0.1 MPa) molar enthalpies of formation, in gas phase, of flavone and flavanone. These results were obtained by combining the standard molar enthalpies of formation in the condensed phase with the standard molar enthalpies of sublimation. The former values were derived from combustion experiments in oxygen, at T = 298.15 K, in a static bomb calorimeter. The values of the standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry and corrected to T = 298.15 K. High-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets and more accurate correlated computational techniques of the MCCM/3 suite have been performed for the compounds. The obtained results, experimental and computational, for flavone and flavanone were compared with those obtained for chromone and chromanone, respectively.

Abstract The electrochemical oxidation of CO has been studied on Pt(S)[(n - 1)(1 0 0) x (1 1 0)] electrodes to investigate the effect of the step density in the reaction. This series shows two different trends for long (n >= 7) and short terraces. For long terraces, the voltammetric peak shifts towards higher potential as the step density increases, unlike the behaviour observed for other stepped surfaces, which exhibit the opposite behaviour in agreement with the Smoluchowski effect. For short terraces, the "normal" behaviour is observed, that is, as the step density increases the peak shifts towards lower potentials. Chronoamperometric measurements were used to determine rate constants and Tafel slopes using the mean field Langmuir-Hinselwood kinetics. Rate constants follow the same trends as the peak potentials in voltammetry. A Tafel slope of 75 +/- 4 mV has been obtained for the surfaces with long terraces whereas a value of the surfaces with short terraces showed a value of 100-120 mV is obtained. This change of slopes is interpreted as a change in the electrochemical behaviour of the species involved in the mechanism, probably, a change in the adsorption isotherm of adsorbed OH. Pt(5 10) electrode exhibits an intermediate behaviour between those of long and short terraces with two different peaks that can be associated with both behaviours previously described.

Abstract The standard (p degrees = 0.1 MPa) molar energies of combustion in oxygen at T = 298.15 K of 5-hydroxy- and 6-hydroxy-alpha-tetralone were measured by static bomb calorimetry. The values of the standard molar enthalpies of sublimation at T = 298.15 K were obtained by Calvet microcalorimetry. Combining these results, the standard molar enthalpies of formation of the compounds in the gas-phase at T = 298.15 K have been calculated: 5-hydroxy-alpha-tetralone -(262.5 +/- 2.3) kJ.mol(-1) and 6-hydroxy-alpha-tetralone -(268.1 +/- 2.2) kJ.mol(-1). Additionally, high-level single-point calculations based on density functional theory with the B3LYP hybrid exchange-correlation energy functional and extended basis sets as well as on two more accurate correlated computational techniques of the MCCM/3 suite have been performed for the studied compounds. The agreement between experiment and theory gives us confidence to estimate the enthalpies of formation of 7-hydroxy and 8-hydroxy-alpha-tetralone. Similar calculations were done for 5-, 6, 7-, and 8-hydroxy-beta-tetralone, for which experimental work was not done.