Chemistry Hydrocarbons MDCAT 2013
PMDC Verified Question 56 of 65
The introduction of an alkyl group in benzene takes place in the presence of \( \text{AlCl}_3 \) and:
A
\( \text{R}-\text{C}(=\text{O})-\text{OH} \)
B
\( \text{R}-\text{C}(=\text{O})-\text{Cl} \)
C
\( \text{R}-\text{Cl} \)
D
\( \text{R}-\text{C}(=\text{O})-\text{O}-\text{R} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: \( \text{R}-\text{Cl} \)
Concept:

Friedel-Crafts alkylation requires an alkylating agent to generate an alkyl carbocation (\( \text{R}^+ \)) when reacted with a Lewis acid catalyst like \( \text{AlCl}_3 \).

Solution:

  • To attach a standard alkyl group (\( \text{R} \)) to benzene, you must start with an alkyl halide.


  • The reagent \( \text{R}-\text{Cl} \) (an alkyl chloride) reacts with \( \text{AlCl}_3 \) to form an \( \text{R}^+ \) electrophile.


  • This electrophile attacks the benzene ring, completing the alkylation.


Why other options are incorrect:

  • \( \text{R}-\text{C}(=\text{O})-\text{Cl} \) (acyl chloride) is used for Friedel-Crafts acylation.


  • \( \text{R}-\text{C}(=\text{O})-\text{OH} \) (carboxylic acid) and ester derivatives do not readily undergo Friedel-Crafts reactions under simple \( \text{AlCl}_3 \) conditions.

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