Inductive Effect - Applications

Applications

• Aliphatic carboxylic acids. The strength of a carboxylic acid depends on the extent of its ionization: the more ionized it is, the stronger it is. As an acid becomes stronger, the numerical value of its pK_a drops. In aliphatic acids, the electron-releasing inductive effect of the methyl group increases the electron density on oxygen and thus hinders the breaking of the O-H bond, which consequently reduces the ionization. Greater ionization in formic acid when compared to acetic acid makes formic acid (pK_a=3.75) stronger than acetic acid (pK_a=4.76). Monochloroacetic acid (pK_a=2.82), though, is stronger than formic acid, since the electron-withdrawing effect of chlorine promotes ionization.
• Aromatic carboxylic acids. In benzoic acid, the carbon atoms which are present in the ring are sp₂ hybridised.As a result, benzoic acid(pK_a=4.20) is a stronger acid than cyclohexane carboxylic acid(pK_a=4.87). Also, electron-withdrawing groups substituted at the ortho and para positions, enhance the acid strength.
• Dioic acids. Since the carboxyl group is itself an electron-withdrawing group, the dioic acids are, in general, stronger than their monocarboxyl analogues.
• In the so-called Baker–Nathan effect the observed order in electron-releasing alkyl substituents is apparently reversed.