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JEE Main · 2026 · 04 Apr 2026 · Shift 2 · Biomolecules

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A D-aldotetrose on oxidation with concentrated resulted in optically inactive dicarboxylic acid. The structure of the D-aldotetrose is:
  1. (A)(see structure)
  2. (B)(see structure)
  3. (C)(see structure)
    ✓ Correct
  4. (D)(see structure)

Answer: (C)

Solution

A D-aldotetrose is with the lowest stereocentre (C-3) hydroxyl on the right in the Fischer projection. Concentrated oxidises both the aldehyde and the terminal to , giving a 2,3-dihydroxybutanedioic (tartaric) acid. This diacid is optically inactive only as its meso form, which needs the two hydroxyls on the same side of the projection. The aldotetrose having both the C-2 and C-3 hydroxyls on the right (D-erythrose) oxidises to meso-tartaric acid, whose internal mirror plane makes it optically inactive, whereas the isomer with the hydroxyls on opposite sides (D-threose) gives an optically active acid. The required D-aldotetrose is D-erythrose, the structure with both hydroxyl groups on the right.

JEE Main · 2026 · 04 Apr 2026 · Shift 2 · Single correct option

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