Electron spin resonance of fluorine-substituted nitro-aromatic anion radicals

Abstract

Electron spin resonance spectra have been observed for anion radicals derived from 2-fluoro-nitro-benzene, 3-fluoro-nitrobenzene, 2,4-difluoro-nitrobenzene, 2,5-difluoro-nitrobenzene, 4-fluoro-2-nitro-phenol, 2-fluoro-6-nitrophenol, and 3-fluoro-6-nitrophenol. All radicals were generated electrolytically in dimethoxyethane/acetonitrile solution, acetonitrile, or dimethylformamide. The radicals are generally quite stable with the exception of those from 2-fluoro-6-nitrophenol and 3-fluoro-6-nitrophenol, the latter decaying with a half-life of approximately 6 min. All spectra can be interpreted completely, and coupling constants are assigned by comparison to related compounds and consistency arguments

The hyperfine coupling constants of some fluorinated free radicals

“…The coupling constants are very similar to those found for the monofluoro radicals in the same solvent and we have included these in table 2 for comparison. The ratios of coupling constants are in good agreement with those recently reported in aprotic solvents [3].…”

“…(The ratios are also lower than in the McLachlan calculations but this is of no significance because the absolute value of p~ is sensitive to the choice of parameters for the fluorine atom.) In a recent paper UHF calculations similar to those reported here have been performed [51] on a number of fuorine containing semiquinones [52] and nitrobenzene radical anions [1][2][3]. The ratios pt~Io/pcc and pcF/pcc were found to be approximately constant and the data could be fitted with QF = 54 G when equation (4) was reduced to equation (2).…”

“…This method can also be used to form the radical anions of substituted nitrobenzenes [1] and we have employed it to record the spectra of the 2,4-difluoronitrobenzene and 2,5-difluoronitrobenzene radical anions in methanol. These have recently been reported in aprotic solvents by Fischer and Zimmerman [3]. The spectra of the monofluoronitrobenzene radical anions in methanol solutions have been published previously [1,16].…”

“…However, much of the data in the literature involves molecules like the fluoronitrobenzene radical anions [1][2][3] which contain other heteroatoms apart from fuorine. The spectra of these radicals are often solvent dependent and are not ideally suited to theoretical investigation.…”

Spin density distributions in some fluorinated radical cations

“…Recently many investigations of the fluorine hyperfine splittings in free radicals containing fluorine have been made using ESR spectroscopy [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Much of the data in the literature involves radical anions of fluoronitrobenzenes [ 1-31 and fluorosubstituted carbonyl compounds [4][5][6][7]141 which contain other heteroatoms apart from fluorine.…”