Relaxation times of aniline derivatives in cyclohexane and 1:4 dioxane

The permittivity (ε′) and dielectric loss (ε″) have been measured at 9.945 GHz for several substituted anilines in cyclohexane and 1:4 dioxane at 35°C. The static permittivity (ε_o) at 300 KHz and high frequency limiting permittivity (ε_∞) have also been measured at 35°C. The dielectric data have been used to yield mean relaxation times and apparent dipole moments. All the compounds studied exhibit an appreciably longer measured relaxation time in p-dioxane than in cyclohexane solution. This indicates that in solvent p-dioxane the free energy of activation for molecular reorientation is increased, probably by hydrogen-bond formation between an oxygen atom of the p-dioxane molecule and an amino-hydrogen atom of substituted anilines. Interaction is also apparent from the difference between their apparent dipole moments in the two solvents and may be dependent upon the volume of the molecule and the protonic character of the hydrogen atom of the amino-group within the substituted anilines. IR studies also confirm this viewpoint.