An Electron Spin Resonance Study of 1,1′- and 2,2′-Biazulenyl Anion Radicals

The electron spin resonance (ESR) spectra of the anion radicals of 1,1′- and 2,2′-biazulenyls have been examined. The ESR spectrum of the latter shows that the unpaired spin is distributed equally between both azulene rings of the molecule. Theoretical calculation of the spin densities by the McLachlan procedure gave satisfactory agreement with the experimentally estimated densities. The ESR spectrum of the anion radical of 1,1′-biazulenyl, which could only be generated by an electrolytic technique, is explained by the fact that the spin exchange between the two halves of the molecule is slow. However, the ESR spectrum of the anion radical of the 3,3′-dicarbethoxy derivative of 1,1′-isomer showed rapid spin exchange through 1,1′-bond.