On the stability and structure of β-fluoro-substituted radical anions of acetamides. An EPR study at 3 K

An EPR study at 3 K of X-ray irradiated monofluoroacetamide does not reveal a radical anion species, despite the fact that the radical anion in trifluoroacetamide is stable at 77 K. This difference in stability has been found to be dependent on the conformation of the -CF₃ group (eclipsed) versus the -CFH₂ group (staggered). The eclipsed conformation permits effective σ-π hyperconjugation in stabilizing the radical anion. An INDO calculation of CF₃CONH₂^? suggests that the radical site is pyramidal rather than planar with a non-planar angle of 32° and a dihedral angle for the eclipsed fluorine, relative to the nearly π-like orbital, of 30°.