Gas-phase thermochemical properties of some tri-substituted phenols: A density functional theory study

The study of the energetics of phenolic compounds has a considerable practical interest since this family of compounds includes numerous synthetic and naturally occurring antioxidants. In this work, density functional theory (DFT) has been used to investigate gas-phase thermochemical properties of the following tri-substituted phenols: 2,4,6-trimethylphenol, 2,6-dimethyl-4-tert-butylphenol, 2,6-dimethyl-4-methoxyphenol, 2,4,6-tri-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-methoxyphenol, 2,4,6-trimethoxyphenol, 2,6-dimethoxy-4-methylphenol and 2,6-dimethoxy-4-tert-butylphenol. Molecular structures were computed with the B3LYP and the ωB97X-D functionals and the 6-31G(d) basis set. More accurate energies were obtained from single-point energy calculations with both functionals and the 6-311++G(2df,2pd) basis set. Standard enthalpies of formation of the phenolic molecules and phenoxyl radicals were derived using an appropriate homodesmotic reaction. The OH homolytic bond dissociation enthalpies, gas-phase acidities and adiabatic ionization enthalpies were also calculated. The general good agreement found between the calculated and the few existent experimental gas-phase thermochemical parameters gives confidence to the estimates concerning the phenolic compounds which were not yet experimentally studied.     

Addendum to “Volumetric properties of binary liquid-phase mixture of (water + glycerol) at temperatures of (278.15 to 323.15) K and pressures of (0.1 to 100) MPa” [J. Chem. Thermodyn. 79 (2014) 135–158]: Effect of pressure on excess thermodynamic characteristics of mixture water + glycerol

Experimentally determined volumetric properties of the liquid binary mixture of {water (1) + glycerol (2)} were processed to calculate the changes of the following thermodynamic parameters with pressure: excess molar Gibbs free energy, ${\mathrm{\Delta }}_{P_o\to P}{G}_m^E$, excess molar entropy, ${\mathrm{\Delta }}_{P_o\to P}{S}_m^E$, excess molar enthalpy, ${\mathrm{\Delta }}_{P_o\to P}{H}_m^E$, as well as the enthalpy of mixing of water and glycerol, $H_m^E$, at 100 MPa. The mixing enthalpies of water and glycerol, $H_m^E$, became more exothermic with pressure increasing at all temperatures studied.     

Thermodynamic mixing properties of liquids in the system Na2O-SiO2

Enthalpies of fusion have been measured by differential scanning calorimetry for a Na₂O-SiO₂ system at 50, 66.6, and 74.4 mol% SiO₂. Enthalpies of mixing of liquids obtained from different calorimetry techniques are critically evaluated. The data on calorimetric enthalpy, activity of Na₂O, cristobalite liquidus, and immiscibility gap are used to determine the enthalpy and entropy of mixing of sodium-silicate liquids are determined as a function of composition by the least squares method. The derived mixing properties are based only on the experimental data and are independent of any assumption about the structure and chemical species in liquids. The enthalpy of mixing has a minimum value of −120 kJ/mol at 35-40 mol% SiO₂ and is convex upward around 80-90 mol% SiO₂. The entropy of mixing have a maximum value of + 6 J/K-mol at 75 mol% SiO₂, and it decreases with the SiO₂ content to −5 J/K-mol at 40 mol% SiO₂. This decrease in entropy can be accounted for by ideal mixing of Q⁴, Q³, and Q^{0 + 1 + 2} (= Q⁰ + Q¹ + Q²) species in the liquids and is responsible for the negative temperature dependence of the partial molar Gibbs energy of mixing of Na₂O, observed in activity measurements. Comparison of the present results with previous values suggests that a quasi-chemical model and the Adam-Gibbs model overestimate the configurational entropy of mixing of liquids.     

G2 PREDICTION OF THE ENTHALPIES OF FORMATION FOR SOME DIATOMIC CATIONS AND NEUTRALS

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Thermodynamics of electrolytes. X. Enthalpy and the effect of temperature on the activity coefficients

Heat of dilution and of solution data are fitted to the form of equation corresponding to that used successfully for activity and osmotic coefficients over a wide range of concentrations. The resulting parameters give the change with temperature of the activity and osmotic coefficients. Results are reported for 84 electrolytes of 1-1, 2-1, 3-1, and 2-2 valence types.     

Di-hydroxybenzenes: Catechol, resorcinol, and hydroquinone: Enthalpies of phase transitions revisited

Molar enthalpies of sublimation of 1,2-di-hydroxybenzene, 1,3-di-hydroxybenzene, and 1,4-di-hydroxybenzene were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. The molar enthalpies of fusion of 1,2- and 1,4-isomers were measured by differential scanning calorimetry (DSC). A large number of the primary experimental results on the temperature dependences of vapor pressure and phase transitions have been collected from the literature and have been treated in a uniform manner in order to derive sublimation, vaporization and fusion enthalpies of di-hydroxybenzenes at the reference temperature 298.15 K. The data sets on phase transitions were checked for internal consistency. This collection together with the new experimental results reported here has helped to resolve contradictions in the available thermochemical data and to recommend consistent and reliable sublimation, vaporization and fusion enthalpies for all three isomers under study.     

Thermodynamical studies of designed ligands binding to Cel7A using partial-filling capillary electrophoresis

A convenient experimental method for thermodynamical studies based on partial-filling affinity CE is presented. The advantages of this approach are the possibility to determine binding energies from relatively weak interactions as well as the small amounts of samples consumed. In order to explore the affinity and selectivity of the cellobiohydrolase Cel7A, a number of propranolol analogues were recently designed. The affinities of a selection of these ligands were determined in the temperature interval 15-40 degrees C, and DeltaG degrees , DeltaH degrees and DeltaS degrees were obtained by means of Van't Hoff plots. Through these experiments, the importance of the entropy contribution in the complexation between the ligands and Cel7A has been demonstrated.