Dielectric studies. Part XIX. Molecular relaxation of some rigid molecules

Abstract

The dielectric absorption at five microwave frequencies of solutions of seven rigid polar molecules in nonpolar solvents has been examined as also has cyclohexanone. Furan, pyridine, and thiophene have their dipole moments along the major axis and their dielectric absorption should be characterized by a single relaxation time. Unlike the monohalobenzenes, camphor, pentamethylene sulfide, tetrahydropyran, and s-trioxan, however, furan, pyridine, and thiophene have non-zero distribution coefficients at 25 °C, whereas for pyridine at 50 °C and cyclohexanone at 25 °C the value is zero. The non-zero distribution coefficients are to be related to either weak solute-solute or solute-solvent interactions, resulting in the polar molecule experiencing a variety of local environments. The observed relaxation times of furan, pyridine, and thiophene are comparable with those of other rigid molecules of similar shape and size. For such cases, even though the distribution parameters are not zero, it is not feasible to analyze the dielectric data into contributions from more than one relaxation process.