Benzopyranyl radicals

The involvement of radicals 36 and 37 in reductions of 2-arylbenzopy-rylium (flavylium) and 1-arylisobenzopyrylium ions is established. 

In general, the radicals dimerize rapidly unless inhibited by pyranyl ring substitution 2-(4-nitrophenyl)benzopyranyl is reported not to dimerize, however.The kinetics of the formation of a series of 36 by reduction of the precursor flavylium ions by Cr(II) have been investigated a Hammett plot of the second-order rate constants versus has p = 1.03. Most work has been concerned with the polarography of the parent cations there appear to be no ESR results for benzopyranyl radicals. The mediation of benzopyranyl radicals in the oxidation of 2-phenyl-2//-benzopyrans by potassium permanganate has been suggested.(See Section II,B,5,b for radicals from anthocyanidins.) 

Vajda and A. Gelleri, Ann. Univ. Sci. Budap. Rolando Eotvos Nominatae, Sect. Chim. 3, 107 (1961) [C.4 57, 8347 (1962)]. 

Vajda and F. Ruff, Abh. Dtsch. Akad. Wiss. Berlin, Kl. Chem., Geol. Biol., 112 (1964) [C 62, 5175(1965)]. 

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