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JEE Main · 2021 · 16 Mar 2021 · Shift 1 · General Organic Chemistry

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Assertion A : Enol form of acetone exists in quantity. However, the enol form of acetyl acetone exists in approximately quantity.
Reason R : Enol form of acetylacetone is stabilized by intramolecular hydrogen bonding, which is not possible in enol form of acetone.
Choose the correct statement:
  1. (A)Both and are true and is the correct explanation of ✓ Correct
  2. (B) is true but is false
  3. (C) is false but is true
  4. (D)Both and are true but is not the correct explanation of

Answer: (A)

Solution

Acetylacetone carries a methylene group between two carbonyls. Its enol places the new double bond in conjugation with the second carbonyl, and the enolic hydroxyl hydrogen is held across a six-membered ring by a hydrogen bond to that carbonyl oxygen. Both effects lower the energy of the enol, and its share at equilibrium rises to about 15 per cent.
Acetone has a single carbonyl, so its enol gains neither the extra conjugation nor an internal hydrogen bond, and the enol content stays below 0.1 per cent.
Both A and R are true and R is the correct explanation of A.

JEE Main · 2021 · 16 Mar 2021 · Shift 1 · Single correct option

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