Practicing Success

Target Exam

CUET

Subject

Chemistry

Chapter

Organic: Haloalkanes and Haloarenes

Question:

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 catalyst is used for the Friedel-Crafts alkylation?

Options:

ZnCl2

anhydrous AlCl3

FeCl3

Both option 2 and option 3

Correct Answer:

Both option 2 and option 3

Explanation:
Alkylation involves the alkylation of an aromatic ring with an alkyl halide using a strong Lewis acid, such as aluminium chloride, ferric chloride,
In Friedel-Crafts alkylation, benzene (and its derivatives) is alkylated with alkyl halide to form alkyl benzene.
In Friedel-Crafts acylation, benzene (and its derivatives) is acylated with acyl halide to form acyl benzene.