MOLECULAR-INTERACTIONS IN CHLOROFORM-DILUENT MIXTURES

Plausible stoichiometries for solution and association complexes in bi nary mixtures of chloroform and one of six organic diluents (n-hexane, p-dioxane, acetone, diethyl ether, tri-n-butyl phosphate, or triethyl amine) are examined parametrically. A range of stoichiometric assumpti ons based on hydrogen bonding are examined, but only a few such combin ations yield statistically significant fits to the experimental vapor- liquid equilibria and NMR chemical shift data. Hydrogen bonding consid erations and the ''true'' chemical species are much more important tha n nonspecific physical factors such as molecular sizes, shape differen ces, and regular solution terms. Thermodynamic equilibrium constants a re presented for the most significant chloroform solvation complexes. Nonspecific dilution shift is important and more helpful in fitting NM R data than the assumption of a chloroform dimer. Physical effects and an orientation factor are used to predict excess enthalpy in chlorofo rm/n-hexane mixtures where no solution or association reactions occur. Model parameters are used to predict excess molar volumes and enthalp ies. Commonly reported stability constants are concentration dependent .