33.1.5—Acidities of chlorine-substituted carboxylic

Chlorine withdraws electron density through sigma bonds. This stabilises the negative charge of a carboxylate ion, so a chlorine-substituted carboxylic acid is more acidic than the unsubstituted acid.

The effect depends on distance: chlorine closer to the carboxyl group exerts a stronger inductive effect, and multiple chlorines reinforce it.

2-chloropropanoic acid is more acidic than propanoic acid; 3-chloropropanoic acid is also stronger than propanoic acid but less strongly affected by the greater separation.

Do not use chlorine’s aromatic directing effects here; acidity is controlled by its inductive withdrawal through the acid’s carbon chain.