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CBSE Class 12 · 2008 · Delhi · BiomoleculesShort Answer

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List the reactions of glucose which cannot be explained by its open-chain structure.

Solution

Facts the open chain cannot explain:
  1. Glucose gives \textbf{no} 2,4-DNP, Schiff or NaHSO reaction — the –CHO is not free.
  2. Glucose \textbf{pentaacetate} does not react with NHOH — the (masked) carbonyl is locked.
  3. Glucose exists as two crystalline forms (α, β) showing \textbf{mutarotation}, and forms two methyl glycosides.
All point to the cyclic hemiacetal (pyranose) structure.

CBSE Class 12 Board · 2008 · Delhi · Subjective

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