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Biomolecules — Chemistry STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceChemistryBiomolecules2 Marks
Question
Write the reactions of D-glucose which can’t be explained by its open-chain structure. How can cyclic structure of glucose explain these reactions?
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Answer

Following reactions and facts could not be explained by open chain structure of glucose.
  • Despite having the aldehyde group, glucose does not give 2,4-DNP test, Schiff’s test and it does not form the hydrogensulphite addition product with NaHSO3.
  • The pentaacetate of glucose does not react with hydroxylamine indicating the absence of free —CHO group.
It was proposed that one of the —OH groups may add to the —CHO group and form a cyclic hemiacetal structure. It was found that glucose forms a six-membered ring in which —OH at C-5 is involved in ring formation.

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