| There are many kinds of solution theories and models at present for the reliable prediction of phase equilibria and excess properties. They are very important and necessary for the development, design, and optimization of separation processes and other applications in industry. Experimental measurements and theoretic researches for basic solution thermodynamics are still fundamentally important in laboratory and industry.Thermodynamic properties for mixing of isomers and enantiomers, which have the similar or same or symmetric functional groups in the molecular structure, are especially difficult to distinct from theoretic models and were so little reports. Searching for correlations between the properties of molecular structures and the thermodynamic properties is very difficult to understand. To clarifiy how these similar molecules constituted a solution in a liquid state mutually recognize each other, and to understand the subjects that to find major interaction power in solution and get correlations between the properties of molecular structures and the thermodynamic properties, the excess enthalpies for series binary mixing of (o+m), (o+p), (m+p)-isomers, homo disubstituted isomers, and 12 binary mixtures of (o-dimethylbenzene+o-isomers) have been measured systematically by the heat-conduction microcalorimeter at 298.15 K in this paper.The subjects of our research were summarized as follows:(1) The excess molar enthalpies for series binary mixtures of (o+m), (o+p) and (m+p)-isomers have been measured by microcalorimeter at 298.15 K. All the measured excess enthalpies were very small. The experimental results were fitted with the Redlich-Kister equation. As convenience to study, isomers were classified into F-group and A-group, which one of the two substituents on benzene ring is fluorine and aliphatic group respectively. The total substituted groups on the benzene ring for all isomers in this study including:-NH2,-CH3,-C2H5,-CH3O,-F,-Cl,-Br,-I,-CN,-NO2, and-CH2CN. A relatively simple formula:H0.5E= a0+a1?m+a2?p was established to reveal the effect of mate and para Hammett constants of the substutied group on excess enthalpies at equalmolar solution H0.5E of (m+p)-isomers. (m+p)-difluorobenzene/chlorofluorobenzene/bromofluorobenzene/ iodofluorobenzene in F-group and (m+p)-fluorotoluene/chlorotoluene/ bromotoluene/iodotoluene in A-group, where?m and?p was the Hammett constants of halogens. The correlated results have a good agreement with the experimental results.The intermolecular interaction (IE) on excess enthalpies for binary mixtures of isomers were computed from quantum chemistry by using the method of MP2/6-311++G(d,p). According to the correlations between IE and excess enthalpies at equalmolar solution H0.5E, the effect of IE on excess enthalpies was considerable different based on A-group and F-group. The slopes of correlations for systems in A-group were close to zero, which of that in F-group were changed from positive to negative from the mixtures of (o+ m)-isomers to (o+p) and (m+p)-isomers. This means the effect of IE on H0.5E for the compounds containing aliphatic-substituted was smaller than that of containing fluorine-substituted isomers.The correlations between the differences of the dipole between the two components of a mixture for binary mixture and H0.5E were also inverstigated. The larger the difference of dipole moment between two compounds of a solution was, the more positive excess enthalpies would be for this mixture. Binary systems of mixtures in A-group showed more stablization compared with that of in F-group.The typical theories of intermolecular force of the pair wise molecules have been reviewed to find out the contributions of dipole-dipole, dipole-induced dipole, dipole-quadrupole, quadrupole-quadrupole interaction energies to the thermodynamic properties by correlated relationships. Based on the rules of correlations, it was consided that the effects on excess enthalpies for F-group mainly came from the different dipole, induce dipole, quadrapole interaction energies, while for A-group mainly came from the different mixtures of (o+ m), (o+p) and (m+p)-isomers.(2) To understand the effect of different substituted groups on thermodynamic properties, the excess molar enthalpies for 12 binary mixtures of (o-dimethylbenzene+o-isomers) have been measured by microcalorimeter at 298.15 K. The Keesom-Debye-London (K-D-L) energies between homo and hetero molecules have been calculated and correlated with H0.5E respectively. The effect of dipole moment on thermodynamic properties becomes visible evidently according to the calculations. For binary mixtures of (o-dimethylbenzene+o-isomers), when o-isomers contains a methyl and a-C2H5 or-CH3O/-F/-Cl/-Br/-I, excess enthalpies decreased rapidly with the increasing of total K-D-L interaction energy(Etotal); while o-isomers contain two substituted groups of halogens, excess enthalpies also decreased with the increasing of Etotal; when these o-isomers contain the substitutes of-CH2CN/-CN/-NH2, which showed unruly behaviours in the correlations.Approximations from the (UNIFAC,Dortmund) model, conductor like screening model for realistic solvents (COSMO-RS), and regular solution theory were compared with the experimental results for (o-dimethylbenzene+ o-isomers) binary system. COSMO-RS approximations were comparatively closed to the experimental results.(3) To reveal the solvent effect on chiral recognition of the enantiomers molecules, microcalorimetric measurements were carried out at 298.15 K to obtain accurate thermodynamic quantities for (R+S)-fenchone and (R+S)-fenchone in different solvents of ethanol, benzene, cyclohexane with different specified molar fractions. Excess enthalpies increased with the decreasing of the specified molar fraction of chiral fenchone in different solvents. Experimental results of (R+S)-fenchone in ethanol solution at equal molar solution H0.5E were compared with the results of (R+S)-limonene in ethanol solution.Excess enthalpies for binary mixture of (S-fenchone+ethanol/benzene/ cyclohexane/carbon tetrachloride) were measured by microcalorimeter and experimental results were compared with the approximations from Modified UNIFAC(Dortmund) model, COSMO-RS theory, and regular solution theory. The predicted results from UNIFAC model had a good agreement with the experimental results. |
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