PK„ values tables

Among diazines, pyridazine has a relatively high pK value (Table I). In general, the introduction of a second nitrogen in the pyridine ring diminishes considerably the basicity and this decrease is in accordance with the theoretical calculations of free valence indices of the nitrogen atoms. The relatively high pK of pyridazine has been attributed to resonance stabilization of the pyridazinium ion. 

The Bronsted correlation for five-membered rings shows that effects of structure on reactivity and on acidity are related. Variations in rate constants for quaternization and in pK values (Table III) are understandable in terms of resonance and inductive effects of the heteroatom X. The effects on the energy of a transition state leading to quaternized product are similar but smaller than those on the energy of protonated material. The following considers in more detail the influence of benzo-fusion. 

The acid strength of proton acid-base pairs (Bronsted acids) is given by the pk value (Table 1.4.2). At the pH that corresponds to the pk, half of the molecules are in the acid form, the other half in the form of the corresponding base. Each pH unit then shifts the ratio by a factor of 10. Phenol, for example, is 50% phenolate and 50% phenol at pH 10, corresponding to a 1 1 ratio at its pk. At pH 7 the ratio of phenohphenolate is then 1000 1. The free energy of acidbase reactions can be directly calculated from the pk values. The pk of water (14 at a concentration of 10 M) is also drastically changed by coordination to metal ions, e.g., to 10 in the coordination sphere of... 

When the separations of the acids within the free and glycine conjugated groups are considered, it is seen that on both columns and thin layers, the cholic acid derivatives are eluted ahead of the derivatives of the deoxycholic and chenodeoxycholic acids, and presumably other dihydroxy bile acids. The derivatives of the lithocholic acid are eluted last. Complete separations of the mono-, di-, and trihydroxy bile acids are not realized even on the thin-layer plates of ion exchangers, and there is no discernible resolution of the various taurine conjugates. This order of elution of the bile acids is opposite to that expected on the basis of their pK values (Table II). Free cholic acid (pK 5.29) would have been expected to be retained longer than the dihydroxy acids (pK 6.18-6.29) which should have been retained... 

Write equations for the acid-base reaction that would occur when each of the following compounds or solutions are mixed. In each case label the stronger acid and stronger base, and the weaker acid and weaker base, by using the appropriate pK values (Table 3.1). (If no appreciable acid-base reaction would occur, you should indicate this.)... 

TABLE VI-L REPRESENTATIVE pK VALUES OF 2-AMINOTHIAZOLES AND 2-IMlNO-4-THIAZOLINES... 

Some ammo acids have side chains that bear acidic or basic groups As Table 27 3 indicates these ammo acids are characterized by three values The third pK reflects the nature of the side chain Acidic ammo acids (aspartic and glutamic acid) have acidic side chains basic ammo acids (lysine arginine and histidine) have basic side chains The isoelectric points of the ammo acids m Table 27 3 are midway between the pK values of the zwitterion and its conjugate acid Take two examples aspartic acid and lysine Aspartic acid has an acidic side chain and a pi of 2 77 Lysine has a basic side chain and a pi of 9 74... 

Table 8.11 pK, Values for Proton-Transfer Reactions in Nonaqueous Solvents 8.81... 

TABLE 8.8 pK, Values of Organic Materials in Water at 25°C Continued)... 

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