Acids and Bases of Biological Interest

A similar solvation effect is found for carboxylic acids (Table 5.51). Formic acid is the most acidic (pKa 3.75) and pivalic acid is the least acidic (pKa 5.03). In both the alcohol and carboxylic acid series, the smaller anion can be better solvated, leading to a larger acidity of the corresponding conjugate acid. 

An interesting trend exists for the acidity of the various ammonium ions (Table 5.7A)  

It is most convenient to analyze the stabilities of these acids themselves to predict acidity instead of analyzing the conjugate bases, because the acids possess the charge. Further, to understand this trend, we must look at two conflicting effects—polarizability and solvation, as has been discussed by Arnett. As presented above in the section on gas phase acidities, the intrinsic acidities of the various ammonium ions follows the following trend  

Apparently, a combination of these two effects leads to the observed trend given at the beginning of this paragraph. 

Since proton transfers are fundamental chemical reactions required in numerous transformations, biology has its own set of acids and bases. For example, two of the classes of amino 

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