Reactions of radical anions. Part X. Electron spin resonance study of the radical anions of azobenzene, naphthalene-1-azobenzene, 1,1′-azonaphthalene, and 2,2′-azonaphthalene including the measurements of tight ion-pair–loose ion-pair equilibria

Abstract

The effect of temperature on the disproportionation equilibria of the radical anions of azobenzene, naphthalene-1-azobenzene, 1,1′-azonaphthalene, and 2,2′-azonaphthalene in tetrahydrofuran with various alkali metals as gegenions has been determined by measurement of the radical-anion concentration at different temperatures by e.s.r. Equilibrium constants, ΔH° values, and ΔS° values have been determined for these disproportionation equilibria.

Well resolved e.s.r. spectra of these radical anions were obtained and analysed and the analysis was compared with the splitting constants obtained from simple Hückel and McLachlan theoretical treatment. The temperature dependence of the metal splittings were measured for azobenzene and naphthalene-1-azobenzene. In all cases except sodium, practically no temperature effect was observed. In the case of sodium, however, a marked temperature dependence of metal splitting and hyperfine splitting line widths were found which have been interpreted in terms of tight ion-pair–loose ion-pair equilibria. Equilibrium constants, ΔH° values, ΔS° values, rate constants, ΔH^‡, and ΔS^‡ values for these equilibria have been determined.