4 -methoxyflavylium compound

Fig. 4 Molar fraction distribution as a function of pH, in aqueous solution at 25 °C, for the 4 -methoxyflavylium compound. Solid lines refer to the species obtained at the thermodynamic equilibrium. Dashed lines refer to species obtained by bringing...

In flavylium compounds that bear OH substituents in their 4 - and/or 7-positions, deprotonation of the OH group can result in other forms being obtained, not seen in the case of the 4 -methoxyflavylium compound discussed above. Figure 8 illustrates this for the 4 -hydroxyflavylium ion.1171 The new species are the quinoidal base A, obtained by simple deprotonation of the AH+ flavylium cation, and the dianionic Cc2- and Ct2- forms, obtained by second deprotonations of Cc and Ct. The roles played by these forms depend on the specific compound and the pH conditions. For... 

As discussed above for the 4,-methoxyflavylium compound, pH jump, temperature jump, and flash photolysis experiments permit the measurement of the rate constants of some of the reactions involved, while steady state titration experiments (using UV-Vis and NMR techniques) enable equilibrium constants to be determined. The values obtained for the most important processes in five flavylium compounds are gathered in Table 1. 

Fig. 11 Energy level diagram for the species involved in the equilibria of the 4 -methoxyflavylium compound.1391...

Fig. 24 Absorption spectra of Co(CN)g and of the Ct and AH+ forms ofthe 4 -methoxyflavylium compound in aqueous solution.

Fig. 25 Changes in absorbance at 434 nm with increasing irradiation time upon continuous irradiation with 365 nm light of solutions containing Co(CN)s and the Ct form of the 4 -methoxyflavylium compound.[20]...

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