Azole radicals neutral

Oxidation of azole anions can give neutral azole radicals which could, in principle, be tt (139) or a- (140) in nature. ESR spectra indicate structure (141 hyperfine splittings in G) for imidazolyl radicals, but both tt- and cr-character have been observed for pyrazolyl radicals. Tetrazolyl radicals (142 4 143) are also well known (79AHC(25)205). Oxidation of 2,4,5-triarylimidazole anions with bromine gives l,l -diimidazolyls (144) which are in equilibrium with the dissociated free radical (145) (70AHQ 12)103). 

A-Alkyl groups in neutral azoles can rearrange thermally to carbon. For example, 2-alkylimidazoles can be prepared in this way in a reaction which is irreversible, uncatalyzed, intramolecular and does not involve radicals (80AHC(27)24l). 

Conditions under which anion-radicals are commonly made, e.g., reaction with an alkali metal in an ethereal solvent, are strongly basic. Azoles without a nitrogen substituent in general, therefore, lose the proton from the heteroatom before the electron is added and, when the latter is added, the product is a dianion radical. Conversely, on oxidation of an azole to give a cation-radical, if the heteroatom is unsubstituted, the proton may be lost, yielding a neutral azolyl radical. Thus, from azoles various radicals may be formed dianion, anion, neutral, or cation-radicals according to the nature of the substituent at N. 

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