Chemistry Hydrocarbons MDCAT 2017
PMDC Verified Question 43 of 65
The reaction of benzene with bromine in the presence of \( \text{FeBr}_3 \) follows the mechanism of ____ reaction.
A
Electrophilic addition
B
Electrophilic substitution
C
Nucleophilic substitution
D
Nucleophilic addition
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Electrophilic substitution
Concept:

Benzene is highly stable due to aromatic resonance. It resists reactions that destroy this stability (like addition) and prefers reactions that restore it.

Solution:

  • \( \text{FeBr}_3 \) generates the strong electrophile \( \text{Br}^+ \) from \( \text{Br}_2 \).


  • The electron-rich benzene ring attacks the electrophile, temporarily breaking aromaticity.


  • To rapidly regain its stable aromatic state, the intermediate expels a proton (\( \text{H}^+ \)), effectively substituting a hydrogen atom with a bromine atom.


  • Therefore, the overriding mechanism is electrophilic substitution.


Why other options are incorrect:

  • Electrophilic addition would leave the ring saturated and non-aromatic, which is thermodynamically highly unfavorable.


  • Nucleophilic reactions involve attack by electron-rich species, but benzene is itself electron-rich and strongly repels nucleophiles.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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