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. The o, p-directing influence of halogen atom can be easily understood if we consider the resonating structures of halobenzene as shown:
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.
Which of the following describes the Fittig reaction?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → An aryl halide is treated with sodium in dry ether, and two aryl groups are joined together.
Sodium in dry ether takes the halogen away from an organic halide as NaX, and the two organic groups left behind are joined together. The name of the reaction depends on which groups are joined. In the Fittig reaction both are aryl groups; chlorobenzene, for example, gives diphenyl:
\( \displaystyle \ce{2C6H5Cl + 2Na} \xrightarrow{\text{dry ether}} \ce{C6H5-C6H5 + 2NaCl} \)
Why the other options are incorrect
Option (2) A mixture of an alkyl halide and an aryl halide is treated with sodium in dry ether to give an alkylarene. — Incorrect. This is the Wurtz-Fittig reaction: an alkyl group and an aryl group are joined, not two aryl groups.
Option (3) An alkyl halide is treated with sodium in dry ether to give a hydrocarbon with double the number of carbon atoms. — Incorrect. This is the Wurtz reaction of alkyl halides; two alkyl groups are joined, so the number of carbon atoms doubles.
Option (4) A freshly prepared benzenediazonium salt is mixed with cuprous chloride, and the diazonium group is replaced by chlorine. — Incorrect. This is the Sandmeyer reaction, a method of preparing haloarenes. No sodium is used and no two rings are joined.
NCERT (2026-27 edition):
6.7.2 Reactions of Haloarenes – “Fittig reaction Aryl halides also give analogous compounds when treated with sodium in dry ether, in which two aryl groups are joined together. It is called Fittig reaction.”