JEE Challenger
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Reaction of Anisole with Hydrogen Bromide

In the reaction

Diagram 0

the products are

Options

A
Option A Diagram 1
B
Option B Diagram 1
C
Option C Diagram 1
D
Option D Diagram 1
Correct

Step-by-Step Solution

To determine the products of the reaction of anisole (C6H5OCH3\text{C}_6\text{H}_5\text{OCH}_3) with hydrogen bromide (HBr\text{HBr}), we analyze the reaction mechanism step by step:

  1. Protonation of the Ether:
    The lone pair of electrons on the oxygen atom of anisole acts as a Lewis base and accepts a proton from HBr\text{HBr} to form an oxonium ion intermediate:
    C6H5−O−CH3+HBr⇌C6H5−OH+−CH3+Br−\text{C}_6\text{H}_5-\text{O}-\text{CH}_3 + \text{HBr} \rightleftharpoons \text{C}_6\text{H}_5-\overset{+}{\underset{\text{H}}{\text{O}}}-\text{CH}_3 + \text{Br}^-

  2. Nucleophilic Attack by Bromide Ion (Br−\text{Br}^-):
    In the protonated ether, there are two potential carbon atoms for nucleophilic attack by the bromide ion:

    • The phenyl carbon (Caromatic\text{C}_{\text{aromatic}}): The bond between the phenyl carbon and the oxygen atom has partial double-bond character due to resonance with the benzene ring. It is stronger and shorter than a typical single bond. Moreover, SN2\text{S}_\text{N}2 displacement at an sp2\text{sp}^2-hybridized aromatic carbon is energetically unfavorable and hindered by electronic repulsion from the π\pi-cloud of the ring.
    • The methyl carbon (Caliphatic\text{C}_{\text{aliphatic}}): The bond between the methyl carbon and the oxygen atom is a normal single bond at an unhindered, sp3\text{sp}^3-hybridized carbon.

    Therefore, the nucleophile Br−\text{Br}^- selectively attacks the methyl carbon via an SN2\text{S}_\text{N}2 pathway:
    Br−+CH3−OH+−C6H5⟶CH3Br+C6H5OH\text{Br}^- + \text{CH}_3-\overset{+}{\underset{\text{H}}{\text{O}}}-\text{C}_6\text{H}_5 \longrightarrow \text{CH}_3\text{Br} + \text{C}_6\text{H}_5\text{OH}

Thus, the reaction produces phenol (C6H5OH\text{C}_6\text{H}_5\text{OH}) and bromomethane (CH3Br\text{CH}_3\text{Br}).

Therefore, the correct option is D.