Account for the following:
(a) Aromatic carboxylic acids do not undergo Friedel-Crafts reaction.
(b) pKa value of 4-nitrobenzoic acid is lower than that of benzoic acid.
(a) This is because the -COOH group is deactivating and the catalyst AlCl3 gets bonded to -COOH group.
(b) −NO2 group is an electron withdrawing group owing to -I effect. So it stabilises the COO− ion and strengthens the acid in 4-nitrobenzoic acid.