Chemistry Hydrocarbons MDCAT 2015
PMDC Verified Question 53 of 65
Which one of the following is a powerful electrophile used to attack on the electrons of benzene ring?
A
\( \text{FeCl}_2 \)
B
\( \text{Cl}^+ \)
C
\( \text{FeCl}_4^- \)
D
\( \text{Cl}_2 \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( \text{Cl}^+ \)
Concept:

Aromatic rings are electron-rich and require a strongly electron-deficient species (an electrophile) to initiate substitution.

Solution:

  • During the halogenation (chlorination) of benzene, neutral \( \text{Cl}_2 \) is not powerful enough to disrupt the aromatic pi cloud.


  • A Lewis acid catalyst (like \( \text{FeCl}_3 \)) polarizes and breaks the Cl-Cl bond to generate the chloronium ion, \( \text{Cl}^+ \).


  • \( \text{Cl}^+ \) has a complete positive charge and an empty orbital, making it a powerful electrophile that can successfully attack the benzene ring.


Why other options are incorrect:

  • \( \text{Cl}_2 \) is relatively weak and neutral.


  • \( \text{FeCl}_4^- \) is a negatively charged complex ion (a nucleophile/base), not an electrophile.


  • \( \text{FeCl}_2 \) is a salt of Iron(II), not the active attacking species.

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