Which one of the following is not formed when acetone reacts with 2-pentanone in the presence of dilute NaOH followed by heating ? 1. [structure in figure] 2. [structure in figure] 3. [structure in figure] 4. [structure in figure]

Answer: 3. [structure in figure] Key idea: in crossed aldol condensation with NaOH, either ketone can give the enolate and either can be the acceptor; dehydration gives an enone. Acetone + acetone gives mesityl oxide (option 2). 2-Pentanone C-3 enolate attacking acetone gives mathrmCH₃CO-C(Et)=C(CH₃)₂ (option 1). Acetone enolate attacking 2-pentanone gives mathrmCH₃CO-CH=C(CH₃)CH₂CH₂CH₃ (option 4). Option 3 has 10 carbons, but acetone (3 C) plus 2-pentanone (5 C) can give at most 8 carbons, so it cannot be formed.

Topic: Alpha-hydrogen acidity, aldol, Cannizzaro, haloform· Organic Compounds Containing Oxygen

Which one of the following is not formed when acetone reacts with 2-pentanone in the presence of dilute NaOH followed by heating ?

four skeletal structures of enones

1. [structure in figure]

2. [structure in figure]

3. [structure in figure]

4. [structure in figure]

Doubtly Asked 30 Oct 2026 NEET UG 2022 Practice test neet Save WhatsApp Report

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Answer: 3. [structure in figure]

Key idea: in crossed aldol condensation with NaOH, either ketone can give the enolate and either can be the acceptor; dehydration gives an enone.

Acetone + acetone gives mesityl oxide (option 2).
2-Pentanone C-3 enolate attacking acetone gives \(\mathrm{CH_3CO{-}C(Et){=}C(CH_3)_2}\) (option 1).
Acetone enolate attacking 2-pentanone gives \(\mathrm{CH_3CO{-}CH{=}C(CH_3)CH_2CH_2CH_3}\) (option 4).
Option 3 has 10 carbons, but acetone (3 C) plus 2-pentanone (5 C) can give at most 8 carbons, so it cannot be formed.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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Which one of the following is not formed when acetone reacts with 2-pentanone in the presence of dilute NaOH followed by heating ?

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