The static electric permittivity of solutions of organic molecules in dipolar solvents

The permittivity of solutions of pyrazine and of 1,4-diazabicyclo-[2,2,2]-octane (TED) in various dipolar solvents has been measured at 10 MHz by means of a sensitive bridge method. The solvents used were water, methanol, formamide, N-methylformamide, N,N-dimethylformamide, and dimethylsulfoxide. The results of the measurements are compared with those of theoretical mixture formulas. It is shown that — depending on structural properties — the permittivity attributed to the solvation shells around the organic solute molecules is changed with respect to the pure solvent value.