Publications

Abstract This work is part of a comprehensive study of the thermal properties of several molecules of tetradentate Schiff bases, obtained as condensation products of salicylaldehyde with alkyldiamines. Herein, we report an experimental thermochemical study of SALPN (N,N'-bis(salicylaldehydo)propylenediimine) and a computational thermochemical study of SALEN (N,N' -bis(salicylaldehydo)dimethylenediimine), SALPN and SALBUTEN (N,N'-bis(salicylaldehydo)tetramethylenediimine) ligands. The standard (p degrees =0.1 MPa) molar enthalpy of formation of crystalline SALPN, at T = 298.15 K, was determined using the static-bomb calorimetry technique. Also, the enthalpy of fusion of this ligand has been determined by differential scanning calorimetry. Additionally, using quantum chemical calculations at the CCSD(T) level of theory, we have calculated the gas-phase standard molar enthalpies of formation of three Schiff base ligands, SALEN, SALPN and SALBUTEN. Moreover, a computational study of the molecular structures of the ligands has been carried out.

Abstract The energetic study of 2-methylnaphtho[1,2-d] oxazole (MN12O), 2-methylnaphtho-[2,3-d] oxazole (MN23O) and 2-methylnaphtho[1,2-d] thiazole (MN12T) has been performed experimental and computationally. The enthalpies of combustion and sublimation/vaporization of these compounds were determined, respectively, from static or rotating bomb combustion calorimetry and high temperature Calvet microcalorimetry and/or the Knudsen-effusion studies. These experimental data allow derivation of the corresponding gas-phase standard molar enthalpies of formation of the three compounds. Additionally, we have obtained the gas-phase standard molar enthalpies of formation of these three compounds, as well of the 2-methylnaphtho[2,3-d] thiazole (MN23T), through high level ab initio calculations, at the G3(MP2)//B3LYP and DLPNO-CCSD(T)/cc-pVTZ levels of theory. The computational study of the molecular structures of the compounds has been carried out. Furthermore, a relationship between the energetic and structural characteristics of these molecules was also evaluated. (C) 2018 Elsevier Ltd.

Abstract The energetic study of 2-phenylbenzoxazole (PBO), 2-phenylbenzothiazole (PBT), 2-(2-hydroxyphenyl) benzoxazole (HBO) and 2-(2-hydroxyphenyl) benzothiazole (HBT) has been developed either using experimental techniques or computational calculations. The enthalpies of combustion and of sublimation of these compounds were determined and the gas-phase standard molar enthalpies of formation were derived. The experimental techniques used were static or rotating bomb combustion calorimetry, high temperature Calvet microcalorimetry and/or the Knudsen-effusion method. Additionally, we have obtained the gas-phase standard molar enthalpies of formation of these compounds, as well of 2-(2-hydroxyphenyl) benzimidazole (HBI), through high level ab initio calculations, at the G3(MP2)//B3LYP level. The computational study of the molecular structures of all these compounds has been carried out and four possible conformers were observed for the molecules of each compound, where the keto tautomers have always higher energy than the enol forms. Furthermore, the energetic effects associated to the presence of the hydroxyl group on the core of the 2-phenylbenzazole rings, in particular the hydrogen bond network, were also evaluated. (C) 2017 Elsevier Ltd.

Abstract The standard (p(o) = 0.1 MPa) molar enthalpy of formation of crystalline uridine, (C9H12N2O6), was determined from its specific energy of combustion, measured by static bomb combustion calorimetry, in oxygen, at T = 298.15 K, as - (1159.8 +/- 1.8) kJ mol(-1). Gas-phase standard molar enthalpy of formation of uridine was determined as - (992.8 +/- 3.2) kJ mol(-1) from quantum-chemical calculations using the G3(MP2) method. The enthalpy of sublimation of uridine at T = 298.15 K, determined as the difference between standard molar enthalpies of formation of uridine in crystalline and gaseous states, was found to be (167.0 +/- 3.7) kJ mol(-1). (C) 2018 Elsevier Ltd.

Abstract The standard (pA degrees A = 0.1 MPa) molar enthalpy of formation at T = 298.15 K for 4,5-dicyanoimidazole, in the crystalline phase, was derived from the standard molar energy of combustion measured by static bomb combustion calorimetry. This value and the literature value of the standard molar enthalpy of sublimation of the compound allow the calculation of the corresponding gas-phase standard molar enthalpy of formation, at T = 298.15 K. Additionally, theoretical calculations for 4,5-dicyanoimidazole were performed by density functional theory with the hybrid functional B3LYP and the 6-31G(d) basis set, extending the study to the 2,4- and 2,5-dicyanoimidazole isomers. Single-point energy calculations for both molecules were determined at the B3LYP/6-311+G(2df,2p) level of theory. With the objective of assessing the quality of the results, standard ab initio molecular orbital calculations at the G3 level were also performed. Enthalpies of formation, obtained using appropriate working reactions, were calculated and compared with the experimental data.

Abstract Condensed phase standard (p degrees = 0.1 MPa) molar enthalpies of formation for 2-coumaranone and 3-coumaranone were derived from the standard molar enthalpies of combustion, in oxygen, at T = 298.15 K, measured by mini-bomb combustion calorimetry. Standard molar enthalpies of sublimation of both isomers were determined by Calvet microcalorimetry. These results were combined to derive the standard molar enthalpies of formation of the compounds, in gas phase, at T = 298.15 K. Additionally, accurate quantum chemical calculations have been performed using DFT methods and high level composite ab initio calculations. Theoretical estimates of the enthalpies of formation of the compounds are in good agreement with the experimental values thus supporting the predictions of the same parameters for isobenzofuranone, an isomer which has not been experimentally studied. The relative stability of these isomers has been evaluated by experimental and computational results. The importance of some stabilizing electronic intramolecular interactions has been studied and quantitatively evaluated through Natural Bonding Orbital (NBO) analysis of the wave functions and the nucleus independent chemical shift (NICS) of the studied systems have been calculated in order to study and establish the effect of electronic delocalization upon the relative stability of the isomers.

Abstract The vapour pressures of the three crystalline isomers of aminobenzamide were measured using the Knudsen mass-loss effusion technique. From the temperature dependence of the vapour pressures, the standard (p degrees = 0.1 MPa) molar enthalpies, Gibbs energies and entropies of sublimation, at T = 298.15 K, were derived. The standard molar enthalpies of formation of the three isomeric aminobenzamides in the crystalline phase, at T = 298.15 K, were determined from static bomb calorimetric experiments. These values were combined with the results of standard molar enthalpies of sublimation to derive the standard molar enthalpy of formation in gaseous phase, at T = 298.15 K, of ortho-aminobenzamide, -(113.1 +/- 1.5) kJ.mol(-1), meta-aminobenzamide, -(98.9 +/- 1.6) kJ.mol(-1), and para-aminobenzamide, -(100.3 +/- 1.6) kJ.mol(-1). The temperature and molar enthalpy of fusion of the studied compounds were measured using differential scanning calorimetry. Additionally, very high-level quantum-chemical calculations at the composite G3 level have been conducted in an attempt to accurately describing the energetic of all isomers. The experimentally observed enthalpies of formation have been fully corroborated by the very accurate calculations.

Abstract The standard (p = 0.1 MPa) molar enthalpy of formation of 6,7-dihydro-4(5H)-benzofuranone was measured, at T = 298.15 K, by static bomb calorimetry and the standard molar enthalpy of vaporization, at T = 298.15 K, was obtained using Calvet microcalorimetry. These values were combined together to derive the standard molar enthalpy of formation of the title compound in gaseous phase, at T = 298.15 K, -(226.0 +/- 2.8) kJ . mol (1). [GRAPHICS] Additionally, density functional theoretical calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets and also other higher-level ab initio quantum calculations have been performed.

Abstract We have performed a study of the structure and energetics of some chlorohydroxypyridines based on experimental calorimetry techniques and high level ab initio computational calculations. The standard (p degrees = 0.1 MPa) molar enthalpies of formation of 2-chloro-3-hydroxypyridine (2-Cl-3-OHPy), 2-chloro-6-hydroxypyridine (2-Cl-6-OHPy) and 3-chloro-5-hydroxypyridine (3-Cl-5-OHPy) in the crystalline phase, at T = 298.15 K, were derived from the respective standard massic energies of combustion measured by rotating-bomb combustion calorimetry, in oxygen, at T = 298.15 K. The standard molar enthalpies of sublimation, at T = 298.15 K, were measured by Calvet microcalorimetry. From these experimentally determined enthalpic parameters we have derived the standard molar enthalpies of formation of the three compounds in the gaseous phase, at T = 298.15 K: 2-Cl-3-OHPy, -(76.8 +/- 2.0) kJ . mol(-1); 2-Cl-6-OHPy, -(105.0 +/- 1.7) kJ . mol(-1), 3-Cl-5-OHPy -(61.2 +/- 2.4) kJ . mol(-1). These values were compared with estimates obtained from very accurate computational calculations using the G3(MP2)//B3LYP composite method and appropriately chosen reactions. These calculations have also been extended to the remaining chloro hydroxypyridine isomers that were not studied experimentally. Based on B3LYP/6-31G* optimized geometries and calculated G3(MP2)//B3LYP absolute enthalpies some structure-energy correlations were discussed.

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressures of the three crystalline isomers of methylbenzamide. From the temperature dependence of the vapour pressures, the standard molar enthalpies of sublimation and the enthalpies of the intermolecular hydrogen bonds N-H center dot center dot center dot O were calculated. The temperature and molar enthalpy of fusion of the studied isomers were measured using differential scanning calorimetry. The values of the standard (p degrees = 0.1 MPa) molar enthalpy of formation in the crystalline phase, at T = 298.15 K, of the compounds studied were derived from their standard massic energies of combustion measured by static-bomb combustion calorimetry. From the experimental values, the standard molar enthalpies of formation in the gaseous phase, at T = 298.15 K, were calculated and compared with the values estimated by employing computational calculations that were conducted using different quantum chemical methods: G3( MP2), G3, and CBS-QB3. Good agreement between experimental and theoretical results is verified. The aromaticity of the compounds has been evaluated through nucleus independent chemical shifts (NICS) calculations.