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We know that in case of halogens, inductive effect is more dominant than resonance effect. So, the 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?

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Where are you getting your information ? So far as I can find 4-Cl-benzoic acid has a pKa of 3.98 and benzoic is 4.2.

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No! -COOH is meta directing group and hence it isn't stabilised at the para position. Hence benzoic acid is more acidic than para-chloro benzoic acid(because the resonating structure of benzoic acid is more stable than p-chloro benzoic acid due to the reason mentioned above).

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    $\begingroup$ The meta para comes in external electrophilic attack, not in acidity. For acidity, we have to consider in which case COOH can easily lose its proton. If more electron withdrawing group is attached to COOH its acidity increases $\endgroup$ – Soumik Das Feb 19 '18 at 9:27
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    $\begingroup$ 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. $\endgroup$ – Soumik Das Feb 19 '18 at 9:37

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