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JEE Main · 2023 · 01 Feb 2023 · Shift 2 · Biomolecules

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All structures given below are of vitamin C. Most stable of them is :
  1. (A)(see structure)
    ✓ Correct
  2. (B)(see structure)
  3. (C)(see structure)
  4. (D)(see structure)

Answer: (A)

Solution

All four structures are tautomers of ascorbic acid, and the most stable is the one in which the five-membered lactone ring carries the ene-diol grouping, with the two hydroxyls on the carbon–carbon double bond directly conjugated to the lactone carbonyl. This conjugation, reinforced by intramolecular hydrogen bonding, delocalises the electrons and provides stabilisation that the diketo tautomers lack. The most stable form is the ene-diol lactone of vitamin C.

JEE Main · 2023 · 01 Feb 2023 · Shift 2 · Single correct option

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