Cinnolinones structure

There is a discrepancy in the literature concerning 4-hydroxy-cinnoline. Whereas two measurements of pKa values indicate that the cinnolinone structure predominates by a large factor in aqueous solution (see Table III), comparison of the ultraviolet spectra of 4-hy-... 

Note The structure and bonding of 2-methyl-3(2//)-cinnolinone (85), 1-methyl-4(l /)-cinnolinone (86, R = H), l-ethoxycarbonylmethyl-4(l//)-cinnolinone (86, R = COaEt), 2-methylcinnolin-2-ium-4-olate (87, R = H), and 2-ethoxy-carbonyImethylcinnolin-2-ium-4-olate (87, R = COaEt) have been examined by X-ray analysis, nuclear quadrupole resonance, and ab initio calcula-tions " ° ° ° X-ray analyses for l-[2-(hydrazinocarbonyl)ethyl]- (88, R = NHNH2) and l- 2-[(pyrrolidin-l-yl)carbonyl]ethyl -4(l//)-cinnolinone [88, R = N(CH2)s] have been reported. ... 

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