MICROWAVE ABSORPTION AND MOLECULAR STRUCTURE IN LIQUIDS .73. A DIELECTRIC STUDY OF SOLUTE-SOLVENT INTERACTIONS

Measurements of dielectric constant and loss at 0.2, 1.2, 3.2, 10.0, and 25.0 cm have been made for seven chloroethanes in dilute cyclohexane, benzene, p-xylene, mesitylene, and p-dioxane solutions at 20-55°. The data have been used to calculate mean relaxation times and apparent dipole moments. For each ethane the mean relaxation time increases with increased solvent basicity, and an approximately linear relationship exists between the solute relaxation time and the ionization potential for the hydrocarbon solvents. In general, this behavior is interpreted in terms of weak solute-solvent interaction, probably C-H hydrogen bonding, hindering the rotation of the chloroethanes. The relative interactions for the solutes in each of the solvents capable of acting as proton acceptors are obtained by reference to their relaxation times in cyclohexane and may be expressed in terms of the increased free energies of activation for molecular rotation amounting to 150-850 cal/mol. In certain cases interaction is lso evidenced by the solvent dependency of the apparent dipole moments. © 1969, American Chemical Society. All rights reserved.