Question

Pka value of 4 nitrobenzoic acid is lowerthan that of benzoic acid.why

Answer 1

since nitro is electron withdrawing group which increases acidity of 4 nitrobenzoic acid

Answer 2

They however do not undergo Friedel–Crafts reaction because the

carboxylic group is deactivating and the catalyst aluminium chloride

(Lewis acid) gets bonded to the carboxylic group.

Para-nitro benzoic acid is more acidic than benzoic acid because of the

electron-withdrawing nitro group at the para position to the acid group.

The nitro group (-NO2) withdraws the electrons from the carboxylic acid

group due to which the electron density on the hydrogen atom of the

carboxylic acid becomes low, and it can be easily removed. Hence, it is

more acidic than benzoic acid.