The results of a study aimed at improvement of group-contribution
methodology for estimation of
thermodynamic properties of organic substances are reported.
Specific weaknesses where particular group-contribution terms were unknown, or estimated because of lack of
experimental data, 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 enthalpies of
formation of acetic acid, (Z)-5-ethylidene-2-norbornene,
mesityl oxide (4-methyl-3-penten-2-one), 4-methylpent-1-ene, glycidyl phenyl ether (1,2-epoxy-3-phenoxypropane), and
2,2‘-bis(phenylthio)propane are
reported. An enthalpy of formation of 2-aminoisobutyric acid
(2-methylalanine) in the crystalline phase
was determined. Using a literature value for the enthalpy of
sublimation of 2-aminoisobutyric acid, a
value for the ideal-gas enthalpy of formation was derived. An
enthalpy of fusion was determined for
2,2‘-bis(phenylthio)propane. Two-phase (solid + vapor)
or (liquid + vapor) heat capacities were determined
from 300 K to the critical region or earlier decomposition temperature
for all the compounds except acetic
acid. For mesityl oxide and 4-methylpent-1-ene, critical
temperatures and critical densities were
determined from the DSC results and corresponding critical pressures
derived from the fitting procedures.
Group-additivity parameters and ring strain energies useful in the
application of group-contribution
correlations were derived.