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A very stable biradical, 2, was prepared from 1 (see picture). The deep-blue/violet biradical was stable in the air for several minutes. The sp2-hybridized carbon radical centers of 2 were confirmed by X-ray crystallography and its reversible oxidation was characterized by cyclic voltammetry. Mes*=2,4,6-tBu3C6H2.
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Sugiyama et al. (2003) studied this question.
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