# Why is benzoic acid more acidic than p-chlorobenzoic acid?

We know that in case of halogens, inductive effect is more dominant than resonance effect. So, the -$$\ce{Cl}$$ on the para position will withdraw electrons by a -I effect and should make p-chlorobenzoic acid more acidic than benzoic acid. But why is it not so? Am I missing something?

Where are you getting your information? So far as I can find, 4-chlorobenzoic acid has a $$\mathrm{p}K_\mathrm{a}$$ of $$3.98$$ and benzoic is $$4.2$$.
• The resonance with Benzene deatabilises conjugate bases if you think properly.Resonance is less favoured in P chloro benzoic acid as +ve charge is created near Cl which is unstable due to -I . So electron pair on $O^-$ can get delocalise very easily in ap chloro benzoic acid rather than benzoic acid. So acidity of Benzoic acid less than p chloro benzoic acid. – Soumik Das Feb 19 '18 at 9:37