Substituent effects on electron spin distribution and conformation of radical ions obtained from 9-diphenylmethylenefluorenes

Abstract

Nine new substituted 9-diphenylmethylenefluorenes were synthesized. The reductions of the unsubstituted hydrocarbon and eleven substituted derivatives were studied by cyclic voltammetry in dimethylformamide solution. E.s.r. and ENDOR spectra of the radical anions obtained by reduction with alkali metal in tetrahydrofuran were recorded. The electron spin distribution as obtained from experiment was compared with the results of Hückel–McLachlan calculations. The conformations of the radical anions were determined from the spectra. The ratio of electron spin densities in the fluorene part of the alkene and in the diphenylmethylene group obeys a linear Hammett correlation. A similar study was performed for the radical cations of six of the twelve alkenes.