Molecular interactions in chloroform-diluent mixtures

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Abstract

Plausible stoichiometries for solvation and association complexes in binary mixtures of chloroform and one of six organic diluents (n-hexane, p-dioxane, acetone, diethyl ether, tri-n-butyl phosphate, or triethylamine) are examined parametrically. A range of stoichiometric assumptions based on hydrogen bonding are examined, but only a few such combinations yield statistically significant fits to the experimental vapor–liquid equilibria and NMR chemical shift data. Hydrogen bonding considerations and the “true” chemical species are much more important than nonspecific physical factors such as molecular sizes, shape differences, and regular solution terms. Thermodynamic equilibrium constants are presented for the most significant chloroform solvation complexes. Nonspecific dilution shift is important and more helpful in fitting NMR data than the assumption of a chloroform dimer. Physical effects and an orientation factor are used to predict excess enthalpy in chloroform/n-hexane mixtures where no solvation or association reactions occur. Model parameters are used to predict excess molar volumes and enthalpies. Commonly reported stability constants are concentration dependent.

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