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JEE Main levelSingle correct optionDifficulty 2 of 3g2185

5-Hydroxypentanal exists in equilibrium with a cyclic ring-chain tautomer formed by addition of the hydroxyl group to the aldehyde group. The ring tautomer is

  1. Aoxolan-2-ol (tetrahydrofuran-2-ol)
  2. Boxan-3-ol
  3. Ccyclopentanol
  4. Doxan-2-ol (tetrahydropyran-2-ol)

Answer: D

The on C-5 attacks C-1 (), giving a cyclic hemiacetal. The ring contains O and C-1 to C-5, so it is six-membered (oxane), and the new is on the carbon next to the ring oxygen, position 2. So the product is oxan-2-ol.
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