Which of the following compounds shall NOT produce propene by reaction with HBr followed by eliminat

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Question

Which of the following compounds shall NOT produce propene by reaction with HBr followed by elimination, or by direct elimination?

Accepted Answer

Correct Answer: A — H₂C=C=O (Ketene)Step-by-step Solution:Trace the pathway for each compound:Option B: 1-Bromopropane on E2 elimination (with base) directly gives propene (CH₃CH=CH₂). Gives propene.Option C: Cyclopropane reacts with HBr by ring-opening addition to give 1-bromopropane. 1-Bromopropane then undergoes elimination to give propene. Gives propene.Option D: Propan-1-ol + HBr → 1-bromopropane; elimination gives propene. Gives propene.Option A: Ketene (H₂C=C=O) reacts with HBr by electrophilic addition across the C=C of the cumulene system to give CH₃COBr (acetyl bromide). This is a 2-carbon acyl bromide — it has no 3-carbon chain and cannot produce propene by any subsequent elimination step.Why other options are incorrect:Options B, C, and D all contain a 3-carbon skeleton or generate one during the reaction, allowing propene to be formed via elimination.Key Concept: Elimination reactions (E1, E2) require a β-hydrogen with respect to the leaving group. Ketene is a 2-carbon compound; its reaction with HBr gives an acyl bromide (not a propyl species), so no 3-carbon alkene can be formed. The 3-carbon chain is a prerequisite for producing propene.

Which of the following compounds shall NOT produce propene by reaction with HBr followed by elimination, or by direct elimination?

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Which of the following compounds shall NOT produce propene by reaction with HBr followed by elimination, or by direct elimination?

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