Substituent effects in fluoren-9-one ketyls. Part 2. The electrolytic reduction of fluoren-9-ones studied by cyclic voltammetry and electron spin resonance spectroscopy

Abstract

A series of fluorenones bearing substituents in positions 2 or 3 was reduced electrolytically in NN-dimethylformamide solution using tetrabutylammonium perchlorate as supporting electrolyte. The resulting species were proved to be the one-electron reduction products, i.e. the paramagnetic radicalanions. The half-wave reduction potentials were determined by cyclic voltammetry. Correlation analysis of the reduction potentials versus the substituent constants was used to show that the transmission of substituent effects through the unsubstituted ring is important for fluorenones substituted in position 2, but unimportant if the substituent is attached to position 3. The hyperfine structure of e.s.r. spectra of the paramagnetic solutions was interpreted and the coupling constants assigned from the results of semiempirical spin density calculations. In most cases the effect of substituents on the electron spin distribution was found to be relatively slight.