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Two important molecular parameters, namely, the dielectric relaxation time and electric dipole moment are highly useful in having insight into the molecular structure, size, shape, apart from the inter-and intra-molecular forces, etc. With these in view dielectric measurements in benzene at room temperature on the pure samples of o-ethyl phenol, 2-n-butylphenol, 4-n-butylphenol, 2,6-dimethoxyphenol and 3,4-difluorophenol were carried out at a frequency of 9.98 GHz by employing concentration variation method. Similar measurements, on a single weight fraction of each of them at 9.98 GHz and also at 8.74 GHz are carried out. Measurements on a single weight fraction in benzene of each of the liquid crystal samples, namely, EPCP.car (Butyl-p-(p-ethoxy phenoxy corbonyl)-phenyl carbonate), PPPB (p-pentylphenyl-p-propyl benzonate), EPAP.Hp (p-(p-ethoxyphenyl azo) phenyl heptenate) and EPAP. Und (p-(p-ethoxyphenyl azo) phenyl undecylenate were also carried out at the said two frequencies. Using the obtained values of " 0 , " 00 relaxation time and dipole moment were determined using different methods. The obtained results are compared with earlier results wherever available.

The variation of dielectric relaxation time with the viscosity of the medium is being exploited in drawing certain quantitative conclusions regarding molecular motion and intermolecular forces in liquids, liquid mixtures, dilute solutions and multi-component polar solutes in dilute solution. With no perfect empirical or theoretical equation in place for the variation of dielectric relaxation time with viscosity, the experimental investigations on different systems only can give an insight. In the present study the results of dielectric measurements carried out on pure samples of o-ethyl phenol, 2-n-butylphenol, 4-n-butylphenol, and 2,6-butylphenol in dilute solutions in different mixed solvents (benzene þ paraffin) and on binary mixtures (1 : 1) of p-2-n-butylphenol þ 4-nbutylphenol and p-bromonitrobenzene þ 2,6-butylphenol, are reported. For comparison, the results on p-bromonitrobenzene þ m-bromonitrobenzene as an example of mixture of nonassociative liquids was also carried out and the results are presented. Different parameters determined using these dielectric measurements are also presented using different models and these studies indicate that the dielectric behavior at microwave frequencies favor the concept of dynamic viscosity and a single viscoelastic relaxation time for the system under study.