14.6: Acidity and Basicity of Carboxylic Acid Derivatives
Carboxylic acids are the strongest among organic acids, as they readily lose the hydroxyl proton to form a resonance-stabilized carboxylate ion. In comparison, the acid derivatives lack acidic hydrogens directly attached to a functional group. In these compounds, the acidic nature arises from their ability to lose α hydrogens, making them weakly acidic.
The relative acidic strength of the derivatives can be explained based on the extent of resonance stabilization of the conjugate base. The higher the stability of the conjugate base, the stronger the acid. The stability of the conjugate base increases from nitriles to acid halides, as shown below:
As a result, nitriles are the weakest acids in the series, whereas acid halides are the strongest.
Similarly, the basicity can be evaluated based on the stability of the conjugate acid, which increases from nitriles to amides as shown below:
Accordingly, nitriles are the weakest bases and amides the strongest.