Physic Department, Bareilly College, Bareilly, 243005 (India)
Email: aksnmr@gmail.com

Present communication reports the experimental values of the dielectric relaxation time  of five polar molecules of 2, 5- Dichloronitrobenzene, 3, 5- Dichloronitrobenzene, 2, 5-Dibromonitrobenzene, 4-Bromonitrobenzene and 2, 4 Dinitrochlorobenzene in dilute solution of benzene at wavelength 3.13 cm in the microwave region. The measurements have been made at 290, 300 and 310 0K, in order to calculate the free energy of activation for dipole orientation process (F). The experimental values of  have been correlated with the calculated value of  obtained using different theories of dielectric relaxation time . It is concluded from this comparative study that the Murty equation is a better representation of the dielectric relaxation phenomenon. Thermo dynamical parameters like molar free energy ofactivation (F), molar enthalpy of activation (H) and molar entropy of activation (S) have been evaluated by considering the relaxation asthe rate process. From the values of F for the various compounds investigated conclusion has been made that energy of activation increases with the size of molecule.