The osmotic coefficients and densities of aqueous and CCl 4 solutions involving 18-crown-6 (18C6) as solute in the concentration range 0.1 to 2.0 m at 25°C were measured. The data obtained is used to calculate activities of solvent and activity coefficient of solute and solvent at 25°C as a function of concentration. It has been observed that activity coefficient of 18C6 increases with increase in concentration of 18C6 while the reverse is true for CCl 4 solutions. Using the partial molar volume of the solute at infinite dilution, the solute-solvent cluster integral values were evaluated which yielded information on solute-solvent interaction. Application of McMillan-Mayer theory enabled us to obtain second and third virial coefficients for solute, which have been decomposed into attractive and repulsive contributions to solute-solute interactions. These are compared with other solutes such as sucrose, glucose, urea, etc. On the basis of attractive and repulsive contributions to solute-solvent and solute-solute interactions in aqueous solutions, the results are interpreted in terms of hydrogen-bonding of water molecules in the crown cavity and hydrophobic stacking interactions mediated through water molecules. The results of CCl 4 solutions are further examined from the point of view of effect of conformational characteristics of 18C6 on the properties in a nonaqueous solvent.

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