Haloarenes undergo the usual electrophilic reactions of the benzene ring such as halogenation, nitration, sulphonation and Friedel-Crafts reactions. Halogen atom besides being slightly deactivating is o, p-directing; therefore, further substitution occurs at ortho- and para-positions with respect to the halogen atom. Due to resonance, the electron density increases more at ortho- and para-positions than at meta-positions. Further, the halogen atom because of its –I effect has some tendency to withdraw electrons from the benzene ring. As a result, the ring gets somewhat deactivated as compared to benzene and hence the electrophilic substitution reactions in haloarenes occur slowly and require more drastic conditions as compared to those in benzene.
What is the major product when chlorobenzene reacts with acetyl chloride in the presence of anhydrous AlCl3?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 4-Chloroacetophenone
Acetyl chloride with anhydrous \( \ce{AlCl3} \) carries out Friedel-Crafts acylation: an acetyl group (\( \ce{CH3CO-} \)) replaces a hydrogen of the ring. The chlorine already on the ring is o,p-directing, so the acetyl group enters ortho or para to it:
\( \displaystyle \ce{C6H5Cl + CH3COCl} \xrightarrow{\text{anhyd. }\ce{AlCl3}} \ce{ClC6H4COCH3 + HCl} \)
Both 2- and 4-chloroacetophenone are formed: the ortho product is the minor one and the para product is the major one.
Why the other options are incorrect
Option (1) 2-Chloroacetophenone — Incorrect. It is the ortho product; it is formed, but only as the minor product.
Option (2) 3-Chloroacetophenone — Incorrect. Chlorine directs to ortho and para, so the meta product is not the product of this reaction.
Option (4) 2,4-Dichloroacetophenone — Incorrect. The reaction adds an acetyl group, not a second chlorine, so the product has only one Cl atom.
NCERT (2026-27 edition):
6.7.2 Reactions of Haloarenes
