Thermodynamic properties of pyruvic acid and its methyl ester

© 2018 Elsevier B.V. In present work, a complete study of thermodynamic properties of pyruvic acid and methyl pyruvate in the condensed and gaseous phases was carried out using experimental and theoretical approaches. Enthalpies of combustion and formation of compounds were evaluated using combustion calorimetry. The transpiration method was used to determine the temperature dependence of the vapor pressures of acid and its methyl ester for the vaporization enthalpy calculation. With ab initio calculation it has been determined, that in gas phase pyruvic acid exists predominantly in monomeric form. The values of the enthalpy characteristics of the substances obtained using the composite method G4 were checked for reliability. A good agreement between the calculated and experimental values of the enthalpies of formation of the acid and its methyl ester in the gaseous phase is observed. The methods of quantum chemistry and statistical physics were used to calculate thermodynamic functions of compounds in the ideal gas state in temperature range 298.15–1500 K

Thermodynamic properties of 1,2-cyclohexanediols

© 2015 Pleiades Publishing, Ltd. The enthalpy values for the combustion and formation of crystalline cis and trans-1,2-cyclohexanediols are determined via bomb calorimetry. The vapor pressures of the compounds and their enthalpies of sublimation are measured. Using quantum-chemical methods, the reliability of the experimental data is estimated, the molecular structures of the compounds are studied, and the structures of the most stable conformers are established. The energy values of the intramolecular hydrogen bonds in the diol molecules are found

Experimental and theoretical thermodynamic properties of RS-(±)- and S-(+)-mandelic acids

© 2018 Elsevier B.V. The enthalpies of formation of RS-(±)- and S-(+)-mandelic acids were measured using high-precision combustion calorimetry. Vapor pressures of the acids were measured using the transpiration method. The enthalpies of sublimation of these compounds at 298.15 K were derived from vapor pressure temperature dependencies. Molar enthalpies of the solid state phase transitions were measured by the DSC. Thermodynamic data on mandelic acids available from the published sources were collected and combined with our experimental results. Thermochemical properties of studied compounds were evaluated and tested for internal and external consistency with different approaches. The methods of quantum chemistry and statistical physics were used to calculate thermodynamic functions of compounds in the ideal gas state in temperature range 298.15 K–1500 K

Thermodynamic functions of lactams in the ideal gas state

Thermodynamic functions (enthalpy, entropy, free energy, and heat capacity) of azacycloalkan-2-ones with ring sizes n = 4-8 in the ideal gas state are calculated by means of quantum chemistry and statistical physics, using an anharmonic approximation in the range of 298-1500 K with allowance for all known conformers and optical isomers. Equilibrium structures and total energies of lactams are calculated using the B3LYP/6-311++G(3df, 3pd), B3LYP/aug-cc-pVQZ, and MP2/6-311++G(3df, 3pd) methods, and the anharmonic frequencies of the fundamental vibrations of all the investigated structures were found via B3LYP/6-311++G(3df, 3pd). © 2014 Pleiades Publishing, Ltd

Thermodynamic properties of dimethylene urethane

© 2015 Pleiades Publishing, Ltd. Abstract Enthalpies of the combustion and formation of crystalline dimethylene urethane (oxazolidin-2-one) are determined via combustion calorimetry. The enthalpy of sublimation is determined via the transpiration method, and the enthalpy of fusion is found by means of differential scanning calorimetry. The temperature dependence of the saturated vapor pressure is measured in the range of 323-353 K. Thermodynamic functions in the ideal gas state are calculated using the rigid rotator-anharmonic oscillator model in the range of T = 298.15-1500 K