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JEE Main · 2023 · 01 Feb 2023 · Shift 1 · Biomolecules

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The correct representation in six membered pyranose form for the following sugar [ X ] is
  1. (A)(see structure)
  2. (B)(see structure)
    ✓ Correct
  3. (C)(see structure)
  4. (D)(see structure)

Answer: (B)

Solution

In the Fischer projection of sugar X the hydroxyls lie on the left at C-2 and C-3 and on the right at C-4 and C-5; this is the configuration of D-mannose, the C-2 epimer of D-glucose. On cyclisation to the six-membered pyranose ring the standard rule applies: groups written on the right in the Fischer projection point downward in the ring and those on the left point upward, while the terminal of a D-sugar points upward. This places the hydroxyls at C-2 and C-3 above the ring plane and the hydroxyl at C-4 below it, with up. The ring structure showing hydroxyls up at C-2 and C-3, down at C-4, and up is the correct pyranose form of this sugar.

JEE Main · 2023 · 01 Feb 2023 · Shift 1 · Single correct option

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