NEET 2019 · ChemistryPrevious Year Question

Among the following, the reaction that proceeds through an electrophilic substitution is:

Answer: (B) (B) $C X_{6} H X_{6} + Cl X_{2} AlCl X_{3} C X_{6} H X_{5} Cl + HCl$ . Chlorination of benzene with $Cl X_{2}$ over $AlCl X_{3}$ generates the electrophile $Cl X^{+}$ , which substitutes a ring hydrogen — a classic electrophilic aromatic substitution giving chlorobenzene.

A.(A) $C X_{6} H X_{5} N X_{2} X^{+} I X^{-} + Cu X_{2} Cl X_{2} C X_{6} H X_{5} I + N X_{2}$
B.(B) $C X_{6} H X_{6} + Cl X_{2} AlCl X_{3} C X_{6} H X_{5} Cl + HCl$ ✓
C.(C) $C X_{6} H X_{6} + 3 Cl X_{2} h ν C X_{6} H X_{6} Cl X_{6}$
D.(D) $CH X_{4} + Cl X_{2} Δ CH X_{3} Cl + HCl$

Correct Answer

(B) (B) $C X_{6} H X_{6} + Cl X_{2} AlCl X_{3} C X_{6} H X_{5} Cl + HCl$

Solution & Explanation

Chlorination of benzene with $Cl X_{2}$ over $AlCl X_{3}$ generates the electrophile $Cl X^{+}$ , which substitutes a ring hydrogen — a classic electrophilic aromatic substitution giving chlorobenzene. Option (A) is a Sandmeyer-type ionic substitution of a diazonium salt; option (C) is photochemical free-radical addition of $Cl X_{2}$ to benzene (giving BHC); option (D) is free-radical substitution on methane. Only (B) is electrophilic substitution.

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