Question

Acetophenone when reacted with a base, $ C_6H_5ONa $, yields a stable compound which has the structure

• A.
• B.
• C.
• D.

Hint:

Aldol condensation reactions typically involve the formation of enolate ions, which then react with carbonyl compounds to form beta-hydroxy ketones or aldehydes, which can undergo dehydration to yield stable compounds.

Answer 1

The Correct Option is A

Acetophenone Aldol Condensation Mechanism

1. Enolate Formation (Initiation)

When acetophenone (C₆H₅COCH₃) reacts with sodium ethoxide (C₂H₅ONa):

C₆H₅COCH₃ + C₂H₅O^- → C₆H₅COCH₂^- + C₂H₅OH

The base abstracts an acidic α-hydrogen (pK_a ≈ 20), forming a resonance-stabilized enolate anion.

2. Nucleophilic Addition (Aldol Formation)

The enolate attacks the carbonyl carbon of another acetophenone molecule:

C₆H₅COCH₂^- + C₆H₅COCH₃ → C₆H₅COCH₂CH(OH)C₆H₅

This forms a β-hydroxy ketone (aldol) intermediate.

3. Dehydration (Elimination)

Under basic conditions, the aldol undergoes elimination:

C₆H₅COCH₂CH(OH)C₆H₅ → C₆H₅CH=CHCOC₆H₅ + H₂O

Water is eliminated to form the α,β-unsaturated ketone (chalcone derivative).

Key Observations:

• The reaction follows standard aldol condensation mechanism
• Product stabilization occurs through conjugation (C=C-C=O)
• Sodium ethoxide serves both as base and nucleophile source
• The final product is more stable than the aldol intermediate

Final Product: The stable α,β-unsaturated ketone (1,3-diphenylprop-2-en-1-one)

Therefore, the correct answer is A.

Answer 2

The aldol condensation is an important organic reaction where carbonyl compounds form new carbon-carbon bonds through nucleophilic addition and subsequent dehydration.

Reaction Mechanism:

1. Aldol Addition:
- Requirements: Compounds must have α-hydrogens (e.g., acetaldehyde, acetone)
- Base catalysis: Dilute NaOH or KOH generates the enolate nucleophile
- Key steps:
  1. Deprotonation at α-carbon forms enolate ion
  2. Enolate attacks carbonyl carbon of another molecule
  3. Protonation yields β-hydroxy carbonyl compound

2. Dehydration:
- Conditions: Heating the aldol product
- Process: Elimination of water (E1cb mechanism)
- Result: Forms α,β-unsaturated carbonyl compound with new C=C bond

Key Features:
- Reversibility: Aldol addition is reversible, while dehydration drives reaction forward
- Stereochemistry: Often forms specific diastereomers in crossed aldol reactions
- Applications: Important for synthesizing complex molecules and natural products

Example Transformation:
Acetaldehyde → Aldol (3-hydroxybutanal) → Crotonaldehyde (but-2-enal)