Write the reactions of D- glucose which can’t be explained by its… - Vidyadip

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 $2,4-\ce{DNP}$ test, Schiff’s test and it does not form the hydrogensulphite addition product with $\ce{NaHSO_3}$.
The pentaacetate of glucose does not react with hydroxylamine indicating the absence of free $—\ce{CHO}$ group.

It was proposed that one of the $—\ce{OH}$ groups may add to the $—\ce{CHO}$ group and form a cyclic hemiacetal structure.
It was found that glucose forms a six $-$ membered ring in which $—\ce{OH}$ at $C-5$ is involved in ring formation.

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