THERMODYNAMIC PROPERTIES AND IDEAL-GAS ENTHALPIES OF FORMATION FOR 2-AMINOISOBUTYRIC ACID (2-METHYLALANINE), ACETIC-ACID, (Z)-5-ETHYLIDENE-2-NORBORNENE, MESITYL OXIDE (4-METHYL-3-PENTEN-2-ONE), 4-METHYLPENT-1-ENE, 2,2'-BIS(PHENYLTHIO)PROPANE, AND GLYCIDYL PHENYL ETHER (1,2-EPOXY-3-PHENOXYPROPANE)

The results of a study aimed at improvement of group-contribution meth odology for estimation of thermodynamic properties of organic substanc es are reported. Specific weaknesses where particular group-contributi on terms were unknown, or estimated because of lack of experimental da ta, are addressed by experimental studies of enthalpies of combustion in the condensed phase, vapor-pressure measurements, and differential scanning calorimetric (DSC) heat-capacity measurements. Ideal-gas enth alpies of formation of acetic acid, (Z)-5-ethylidene-2-norbornene, mes ityl oxide (4-methyl-3-penten-2-one), 4-methylpent-1-ene, glycidyl phe nyl ether (1,2-epoxy-3-phenoxypropane), and 2,2'-bis(phenylthio)propan e are reported. An enthalpy of formation of 2-aminoisobutyric acid (2- methylalanine) in the crystalline phase was determined. Using a litera ture value for the enthalpy of sublimation of 2-aminoisobutyric acid, a value for the ideal-gas enthalpy of formation was derived. An enthal py of fusion was determined for 2,2'-bis(phenylthio)propane. Two-phase (solid + vapor) or (liquid + vapor) heat capacities were determined f rom 300 K to the critical region or earlier decomposition temperature for all the compounds except acetic acid. For mesityl oxide and 4-meth ylpent-1-ene, critical temperatures and critical densities were determ ined hom the DSC results and corresponding critical pressures derived from the fitting procedures. Group-additivity parameters and ring stra in energies useful in the application of group-contribution correlatio ns were derived.