The greater acidity of the –OH hydrogen in acetic acid is due primarily to two factors: resonance and inductive effects. In acetic acid, the presence of the neighboring carbonyl group has an electron-withdrawing inductive effect on the –OH hydrogen, increasing its acidity relative to ethanol, in which there is no carbonyl group. Also, comparison of the respective conjugate bases shows that, unlike the ethoxide ion, the acetate ion is stabilized by resonance. This too, is reflected in the greater acid strength of the corresponding acid species.
