Dielectric Relaxation and Molecular Structure. III. Dielectric Relaxation Study of Some Anilines in Benzene Solutions at Different Temperatures

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Measurements of relative permittivity at 1 MHz and at 9.46 GHz, the refractive index for the Sodium D-line, have been made for (a) N,N-dimethylaniline, (b) N,N-diethylaniline, (c) o-chloroaniline, (d) m-chloroaniline and (e) p-chloroaniline at temperatures of 15, 25, 35, and 45°C in dilute solutions of benzene. Dielectric relaxation times τ(1) and τ(2) have been calculated by the method recently suggested by Higasi, Koga, and Nakamura in terms of the slopes a0, a′, a″, and aD. It is remarked that τ(2) at the experimental frequency of 9.46 GHz leads to τ1 the relaxation time for overall rotation, whereas τ(1) becomes an explicit function of τ1 and τ2- These determinations suggest the presence of both molecular and intramolecular rotations in the molecules. The results for τ(2) show a systematic decrease with increase in temperature whereas for τ(1) there seems to be no observable trend. The enthalpy and entropy of activation for molecular dielectric relaxation process has been determined. The enthalpy of activation for (a) and (b) is of the same order of magnitude (i.e., 3 kcal/mol), and the same is true for the case of (d) and (e) (1.8 kcal/mol) but 6.8 kcal/mol for (c). It appears that in o-chloroaniline, there is a finite probability of H–Cl bond formation between one of the amino hydrogens and the neighbouring chlorine atom.
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