E.s.r., ENDOR, and triple resonance of fluoro-substituted fluorenone ketyls

Abstract

Electron spin resonance (e.s.r) and electron nuclear double resonance (ENDOR) spectra have been observed from dilute solutions of the radical anions of 1-,2-,3-, and 4-fluoro- and 2,7-difluoro-fluorenone in tetrahydrofuran (THF) at temperatures below –70 °C with sodium as gegenion. For all the radical anion pairs, both general and special triple resonance experiments were carried out. Similar e.s.r. spectra were obtained for each compound by electrolytic reduction in dimethylformamide (DMF), at room temperature. The e.s.r. spectra have been analysed using coupling constants obtained from the ENDOR experiments. In the cases of the 1-, 2-, and 4-fluoro- and 2,7-difluoro-fluorenone, both ¹H and ¹⁹F absorptions were clearly seen in their multiple resonance spectra. However for 3-fluorofluorenone no ¹⁹F ENDOR absorptions were evident. The ¹H hyperfine couplings are in every case similar to the values determined for the parent unsubstituted fluorenone and were assigned according to the results of Hückel–McLachlan calculations.