Question

Account for the following ;
(1) Aromatic carboxylic acids to not undergo friedel-crafts reaction.
(2) pKa value of 4-nitrobenzoic acid is lower than that of benzoic acid.

Answer 1

the -COOH gp attached to the benzene ring is electron withdrawing with ring deactivating . due to which benzoic acid does not undergo friedal crafts rxn.
2. it is bcz on nitro -I effect so it increase it's acidic strength more than the benzoic acid ....and acidic strength is inversely proportional to the pKa...so 4 nitro benzoic acidic strength more than the benzoic acid...then it's pKa value of 4 nitro benzoic acid is lower than the benzoic acid.