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Biomolecules — Chemistry STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceChemistryBiomolecules2 Marks
Question
Glucose is an aldohexose monosaccharide. Why does it react with hydrogen cyanide to form cyanohydrin but does not react with sodium hydrogen sulphite?
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Answer

D-glucose exist in cyclic forms $\alpha$- and $\beta$- in which the aldehyde group is involved in the formation of a ring and is not free. Therefore, it does not react with NaHSO3. However, with reagents like HCN and phenyl - hydrazine, the ring structure cleaves and the aldehydic group becomes free. Therefore, D-glucose does not react with HCN.

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