enthalpy of formation

The temperature dependence of the saturated vapor pressure and the combustion energy of 2-methyl-5-phenylfuran-3-carboxylic acid were determined by experimental methods. Based on the obtained data, the values of the enthalpies of combustion and formation in the condensed state were calculated. The enthalpy of sublimation was recalculated to 298K. The additive Benson scheme is supplemented with new fragments for calculating the enthalpies of formation in the gaseous state.

The formation of associates in aqueous solutions between single- or double-charged anions of 5,5′-dibromo-o-cresolsulfonphthaleine and single-charged cations of cyanine dyes (quinaldine blue, quinaldine red) has been considered. Based on the spectrophotometric data, the equilibrium constants of the association were analyzed. The energy of cation-anion interactions (standard enthalpy of formation of ions and associates) was determined by the semi-empirical AM1 method and probable structures of associates were set.

Combustion energies of esters (ethyl 6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carboxylate; ethyl 6-methyl-4-(4-methylphenyl)-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate; ethyl 4-(4-methoxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate and ethyl 4-(6-methoxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate) were experimentally obtained using a bomb calorimetry. According to the experimental data, the enthalpies of combustion and the enthalpies of formation in a solid state were calculated.

Using the precision bomb combustion calorimeter B-08-MA, the combustion energies of 5- (2-nitrophenyl) -furan-2-carbaldehyde, 5- (2-nitro-4-methylphenyl) -furan-2-carbaldehyde and 5- ( 2-nitro-4-oxymethylphenyl) -furan-2-carbaldehyde. Based on the obtained data, the values of enthalpies of combustion and formation of substances in the condensed state are calculated. A comparative analysis of experimentally determined values with theoretically calculated values by additive calculation methods is given.

The formation of associates between one- or two-charged anions of sulfonephthalein dyes – thymolsulfonephthalein, cresolsulfonephthalein – and cyanine cations (pinacyanol, quinaldine red) has been considered in aqueous solution. Equilibrium association constants have been determined using spectrophotometric data. By semiempirical methods the enthalpy of formation and the eventual structure of ions and associates have been established.