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Chemistry · PYQ NEET UG 2022
हिन्दीWhich one of the following is NOT formed when acetone reacts with 2-pentanone in the presence of dilute \( \text{NaOH} \) followed by heating?
Correct answer · Option 2
2-Methylhept-2-en-4-one
Explanation
When a mixture of acetone \( (\text{CH}_3\text{COCH}_3) \) and 2-pentanone \( (\text{CH}_3\text{COCH}_2\text{CH}_2\text{CH}_3) \) is treated with dilute \( \text{NaOH} \) followed by heating, mixed aldol condensation (cross-aldol condensation) as well as self-aldol condensation products can be formed because both reactants contain \( \alpha \)-hydrogens.
1. **Self-condensation of acetone:** \( \text{CH}_3\text{COCH}_3 + \text{CH}_3\text{COCH}_3 \rightarrow \text{CH}_3\text{C(CH}_3\text{)}=\text{CHCOCH}_3 \) (4-Methylpent-3-en-2-one).
2. **Self-condensation of 2-pentanone:** 2-pentanone can form enolate from C-1 or C-3. Reaction involving C-1 enolate with another molecule of 2-pentanone yields \( \text{CH}_3\text{CH}_2\text{CH}_2\text{C(CH}_2\text{CH}_3\text{)}=\text{CHCOCH}_3 \) or similar derivatives depending on the active methylene/methyl position.
3. **Cross-condensation products:**
- Acetone enolate attacking 2-pentanone carbonyl gives: 4-methylhept-3-en-2-one.
- 2-pentanone enolate (from C-3) attacking acetone carbonyl gives: 3-methylhept-3-en-5-one.
However, 2-methylhept-2-en-4-one cannot be formed as it would require an improbable enolate and regiochemical attack that does not correspond to the available \( \alpha \)-hydrogens and reaction pathways of acetone and 2-pentanone. Therefore, option 2 is NOT formed.
1. **Self-condensation of acetone:** \( \text{CH}_3\text{COCH}_3 + \text{CH}_3\text{COCH}_3 \rightarrow \text{CH}_3\text{C(CH}_3\text{)}=\text{CHCOCH}_3 \) (4-Methylpent-3-en-2-one).
2. **Self-condensation of 2-pentanone:** 2-pentanone can form enolate from C-1 or C-3. Reaction involving C-1 enolate with another molecule of 2-pentanone yields \( \text{CH}_3\text{CH}_2\text{CH}_2\text{C(CH}_2\text{CH}_3\text{)}=\text{CHCOCH}_3 \) or similar derivatives depending on the active methylene/methyl position.
3. **Cross-condensation products:**
- Acetone enolate attacking 2-pentanone carbonyl gives: 4-methylhept-3-en-2-one.
- 2-pentanone enolate (from C-3) attacking acetone carbonyl gives: 3-methylhept-3-en-5-one.
However, 2-methylhept-2-en-4-one cannot be formed as it would require an improbable enolate and regiochemical attack that does not correspond to the available \( \alpha \)-hydrogens and reaction pathways of acetone and 2-pentanone. Therefore, option 2 is NOT formed.
