Dielectric relaxation in 2-acetylnaphthalene and related compounds

Abstract

The dielectric absorption of 2-acetylnaphthalene and 2- and 3-acetylphenanthrene has been studied in p-xylene solution at several microwave frequencies and in a polystyrene matrix at low frequencies. Acetyl group relaxation has been established from both sets of data. A clear separation of the dielectric absorption of the molecule and the group has been achieved for both 2- and 3-acetylphenanthrene in the matrix. The Eyring activation parameters have been established for acetyl relaxation in these molecules in the matrix. The free energy of activation values for group relaxation increase in the sequence acetophenone < 2-acetylphenanthrene < 3-acetylphenanthrene < 2-acetylnaphthalene. For the p-xylene solution data the weight factor for group relaxation, C2, is appreciably lower than the theoretical value, so that C2 < C1, bearing out the findings of Fong and Smyth for 2-acetylnaphthalene. In polystyrene matrices, the data for 2- and 3-acetylphenanthrene also indicated that C2 < C1. The enthalpy of activation for acetyl relaxation in 2- and 3-acetylphenanthrene is similar to that for acetophenone and 1,4-diacetylbenzene whereas that for 2-acetylnaphthalene would seem somewhat larger.