Chemistry Alkyl Halides SZABMU 2024
PMDC Verified Question 4 of 13
When \( CO_2 \) reacts with propyl magnesium chloride followed by acid hydrolysis, the product formed is ____
A
Butanoic acid
B
Pentanoic acid
C
Ethanoic acid
D
Propanoic acid
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: Butanoic acid
Concept:

The reaction of a Grignard reagent with carbon dioxide (carboxylation) extends the carbon chain by exactly one carbon, forming a carboxylic acid.

Solution:

  • The Grignard reagent is propyl magnesium chloride (\( CH_3CH_2CH_2MgCl \)), which contains a 3-carbon chain.
  • Carbon dioxide (\( CO_2 \)) provides exactly 1 carbon atom.
  • The nucleophilic propyl group attacks the electrophilic carbon of \( CO_2 \), forming a carboxylate salt.
  • Acid hydrolysis protonates the salt: \( C_3H_7 - C(=O)O^- \xrightarrow{H^+} C_3H_7COOH \).
  • The final product has \( 3 + 1 = 4 \) carbons. A 4-carbon carboxylic acid is Butanoic acid.


Why other options are incorrect:

  • Option D: Propanoic acid would form if ethyl magnesium chloride (2 carbons) was used.
  • Option B: Pentanoic acid would require a butyl Grignard (4 carbons).

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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