1 research outputs found
Well-Known Mediators of Selective Oxidation with Unknown Electronic Structure: Metal-Free Generation and EPR Study of Imide‑<i>N</i>‑oxyl Radicals
Nitroxyl radicals are widely used
in chemistry, materials sciences,
and biology. Imide-<i>N</i>-oxyl radicals are subclass of
unique nitroxyl radicals that proved to be useful catalysts and mediators
of selective oxidation and CH-functionalization. An efficient metal-free
method was developed for the generation of imide-<i>N</i>-oxyl radicals from <i>N</i>-hydroxyimides at room temperature
by the reaction with (diacetoxyiodo)Âbenzene. The method allows for
the production of high concentrations of free radicals and provides
high resolution of their EPR spectra exhibiting the superhyperfine
structure from benzene ring protons distant from the radical center.
An analysis of the spectra shows that, regardless of the electronic
effects of the substituents in the benzene ring, the superhyperfine
coupling constant of an unpaired electron with the distant protons
at positions 4 and 5 of the aromatic system is substantially greater
than that with the protons at positions 3 and 6 that are closer to
the <i>N</i>-oxyl radical center. This is indicative of
an unusual character of the spin density distribution of the unpaired
electron in substituted phthalimide-<i>N</i>-oxyl radicals.
Understanding of the nature of the electron density distribution in
imide-<i>N</i>-oxyl radicals may be useful for the development
of commercial mediators of oxidation based on <i>N</i>-hydroxyimides