Why is chloroacetic acid stronger than acetic acid?

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Chloroacetic acid is stronger than acetic acid due to the inductive effect, which describes how substituents influence the distribution of electrons within a molecule.

In acetic acid (H—CH2COOH), the methyl group is electron-donating, which destabilizes the resulting carboxylate ion. In contrast, chloroacetic acid (Cl—CH2COOH) contains a chlorine atom, which has a higher electronegativity than hydrogen. Because of this, the chlorine atom acts as an electron-withdrawing group, pulling electron density away from the carbon atom.

This electron-withdrawing effect stabilizes the negative charge of the carboxylate ion formed after the acid donates its proton. In general, electron-withdrawing groups increase the acidity of carboxylic acids by enhancing the stability of the conjugate base. Consequently, chloroacetic acid is approximately 100 times stronger than acetic acid.12