| Abstract
| - Flash photolysis of 10-diazo-9(10H)-phenanthrenone inaqueous solution was found to give two successivelyformed transient species and to produce fluorene-9-carboxylic acid asthe major reaction product. These transientswere identified, through solvent isotope effects and the form ofacid−base catalysis, as fluorenylideneketene, formedby photo-Wolff reaction of the diazophenanthrenone, andfluorene-9-carboxylic acid enol, formed by hydration ofthis ketene. Analysis of the rate profile of the enol ketonizationreaction produced the first and second ionizationconstants for the enol ionizing as an oxygen acid,= 2.01 and= 9.61, respectively. The rate ofenolization of fluorene-9-carboxylic acid was also determined, bybromine scavenging, and that, coupled with aliterature value of the acidity constant of this acid, allowedevaluation of the two keto−enol equilibrium constants(pKE = 9.67 for interconverting un-ionizedcarboxylic acid and enol and pK‘E = 8.24 forinterconverting singlyionized acid and enol), and it also allowed evaluation of the twocarbon acid acidity constants= 11.67 forionization of the un-ionized carboxylic acid as a carbon acid and= 17.85 for ionization of its carboxylate ionas a carbon acid). (All acidity constants are concentrationquotients applicable at ionic strength 0.10 M.) Theseketo−enol equilibrium constants and acid dissociation constants arelarge because of the enol and enolate ion stabilizingeffects of the cyclopentadienyl ring of the fluorenyl group; this ringalso makes fluorenylideneketene an unusuallyreactive substance.
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