Temperature Effects on Electrode Processes. II. The Entropy of Formation of Ion Radicals of Heteroaromatic Compounds.

Abstract

The temp. dependence of reversible electrode potentials, measured by phase selective second harmonic a.c. voltammetry, for the formation of ion radicals of heteroarom. compds. structurally related to anthracene, was detd. in order to obtain entropies of formation. All compds. examd. had the anthracene nucleus with the 9 and 10 positions occupied by heteroatoms, S, O, N, or Se. The entropy for the formation of the anion radical of phenazine in MeCN was -4.7 cal/K mol, in agreement with that for anthracene anion radical indicating little influence of the N atoms on the charge distribution of the anion radical. The entropies of formation of cation radicals of the heteroaroms. were greater than expected for the anthracene cation radical ranging from +10.0 to +25.3 cal/K mol. Enthalpy changes and reversible potentials, relative to those for the redn. of anthracene, were linearly related with a slope of 0.907. the deviation of the slope from unity shows the importance of entropy changes in the redox processes. [on SciFinder (R)]