| Popis: |
Composite hydrolytic dissociation constants, KI and KII, of 4-aminobenzoic acids substituted as follows, 2-H-, 2-CH3-, 2-Cl-, 2-Br-, 2-NO2-, 2-OH-, 2-OCH3-, 3-Br-, 2,6-(CH3)2-, 2,6-(C2H5)2-, 2,6-Cl2- and 2,6-Br2-, have been determined in aqueous solution, at 50°C and at an ionic strength of 0.1. From the values of pKI and pKII and the postulate that the inductive effect of the 4-NH3+ group on the dissociation of the 1-COOH group is the same for all the acids studied, namely 0.54, all four individual pK values have been calculated for each acid as well as the fraction of zwitterion. After comparison of the individual pK values with the correspondingly substituted benzoic acids and anilinium ions, several conclusions could be drawn with respect to the configurational and energetic relationships between the acids. |
