[en] In this paper a model for viscoanelastic isotropic material in the formalism of Kluitenberg's theory on mechanical relaxation phenomena is considered. Moreover an expression of the complex modulus is obtained to compare the results obtained with experimental data. In particular, by considering the results obtained from some authors of us in a previous paper, we shall use a different condition that allows to get the phenomenological and state coefficients both low and high frequencies. Finally, the results are applied to a supercooled m-toluidine in order to compare the experimental data and theoretical functions of frequency G₁ and G₂ so obtained.