PKa. values

The acids of chlorine(I), bromine(I) and iodine(I) are weak acids, the pKa values being 7.4, 8.7 and 12.3 respectively. They are good oxidising agents, especially in acid solutions. The acids decrease in stability from chloric(I) to iodic(I). 

However, some significant deviations between the experimental and predicted pKa values are visible and some improvements and modifications of the procedure are possible. 

Table 2. Predicted intrinsic and apparent pKa values for the Cys403 residue in Yersinia phosphatase for different models of the structure the data refer to a temperature of 293 K and an ionic strength corresponding to 150 mM of monovalent salt. See the text for the detailed description of the conditions under which each pK estimation was made. The experimentally determined value is 4.67 [39]...

Base is chosen so as to favor enolate formation. Acidity of C-H bond must be greater (lower pKa value) than that of the conjugate acid of the base (C S table 1.1, pg 3)... 

The basicity of a 4-phenyl-substituted thiazole is less than the corresponding methyl-substituted thiazole (16) and the pKa values of quaiemarv salts are in the same order (25). 

EDTA Is a Weak Acid Besides its properties as a ligand, EDTA is also a weak acid. The fully protonated form of EDTA, HeY, is a hexaprotic weak acid with successive pKa values of... 

Table 4 pKa Values of Pyrrole-, Furan-, Thiophene-, Selenophene- and Tellurophene-earboxylie Aeids... 

The pKa values of a number of isoxazoles have been reported and again the weakly basic nature of the ring, being less than oxazole, is demonstrated (see Table 3) (7iPMH(3)i. p. 23). 

Ionisation constants of ionisable compounds are give as pK values (published from the literature) and refer to the pKa values at room temperature ( 15 C to 25 C). The values at other temperatures are given as superscripts, e.g. pK for 25 C. Estimated values are entered as pKgjt (see Chapter 1, p. 7 for further information). 

A large number of substances are ionisable in aqueous solutions and a knowledge of their ionisation constants, stated as pK (pKa) values, can be of importance not only in their purification but also in their reactivity. Literature values of the pK s have been inserted for ionisable substances, and where values could not be found they were estimated (pKesi)- The estimates are usually so close to the true values as not to affect the purification process or the reactivity seriously. The book will thus be a good compilation of pK values for ionisable substances. 

Most organic compounds are bases, that is, they are capable of accepting a proton. The best-studied organic bases are the moderately strong ones, which will receive a proton in dilute aqueous solutions amines are the most important examples. The pKa value of the protonated base, referred to the infinitely dilute aqueous solution, is the usual measure of base strength, and the pH of the solution is a quantitative measure of solvent acidity, or ability to transfer a proton. 

Alcohols are typically very weak acids with pKa values in the range of 7 - 20 (compared with a pK value of 4.8 for acetic acid). 

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