In previous studies, we have used molecular orbital calculations to determine the thermodynamic
changes of dimerization for a number of pure and cross-associated species. We have shown
that by using these results in a physical equation of state, the statistical associating fluid theory
(SAFT), we are able to accurately model the phase behavior of pure self-associating compounds
and binary mixtures of a self-associating compound and a nonassociating compound with a
reduction in the number of adjustable parameters. In this study, we consider the phase behavior
of binary mixtures in which cross-associated species may occur. To determine the equation of
state parameters describing cross association, we introduce a mixing rule based on the results
of our molecular orbital calculations. We show that using information derived from our quantum-mechanical calculations results in correlations of mixture vapor−liquid equilibrium data with
fewer adjustable parameters and no loss of accuracy, indeed frequently with improved accuracy,
compared to the original SAFT model.
We have used Hartree-Fock theory and density functional theory to compute the enthalpy and entropy changes of dimerization for water, methanol, and the family of carboxylic acids. These results are used in a physical equation of state, the statistical associating fluid theory (SAFT), in order to model the phase behavior of these hydrogen-bonding compounds. A procedure has been developed to relate the calculated enthalpy and entropy changes to the association parameters in SAFT using only low-pressure data, as well as to relate molar volumes from molecular orbital calculations to the segment size and chain length parameters in SAFT. By doing so, the SAFT model is reduced to a three-parameter equation of state for associating fluids. The modified equation of state is shown to be as accurate as the original SAFT model for correlating pure-component vapor-liquid equilibrium data with fewer adjustable parameters.
The aluminum complexes (LMes(2-))AlCl(THF) (3) and (LDipp(-))AlCl2 (4) (LMes = N,N'-bis[2,4,6-trimethylphenyl]-2,3-dimethyl-1,4-diazabutadiene, LDipp = N,N'-bis[2,6-diisopropylphenyl]-2,3-dimethyl-1,4-diazabutadiene) were prepared by direct reduction of the ligands with sodium metal followed by salt metathesis with AlCl3. The (LMes(-))AlCl2 (5) complex was prepared through one-electron oxidative functionalization of 3 with either AgCl or CuCl. Complex 3 was characterized using (1)H and (13)C NMR spectoscopies. Single-crystal X-ray diffraction analysis of the complexes revealed that 3-5 are all four-coordinate, with 3 exhibiting a trigonal pyramidal geometry, while 4 and 5 exist between trigonal pyramidal and tetrahedral. Notable in the LMes complexes 3 and 5 is a systematic lengthening of the C-Nimido bonds and shortening of the C-C bond in the N-C-C-N backbone with increased electron density on the ligand. The geometries of the complexes 3 and 5 were optimized using DFT, which showed primarily ligand-based frontier orbitals, supporting the analysis of the solid-state structural data. The complexes 3-5 were also characterized by electrochemistry. The cyclic voltamogram of complex 3 showed an oxidation processes at -0.94 and -0.03 V versus ferrocene, while complexes 4 and 5 exhibit both reduction (-1.37 and -1.34 V, respectively) and oxidation (-0.62 and -0.73 V, respectively) features.
Hartree-Fock theory and density functional theory were used to compute the enthalpy and entropy changes of dimerization for a number of hydrogen-bonding compounds. In Part 1, the calculational methods and procedures use for the water dimer are described, and the results obtained are compared with those of uthers and with experimental estimates in the literature. Here, a variety of organic compounds that can self associate and/or cross associate are considered. The results obtained for the self-association of these compounds are compared with estimates obtained from various types of experimental data. The results are also used to examine the validity of group-contribution methods for hydrogen-bonding mixtures and to test a simple estimation procedure for cross dimerization that can reduce the number of calculations, such as those described here, that need to be done.
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