Question

Which of the following reactions and facts of D-glucose cannot be explained by its open chain structure?

• A. Despite having the aldehyde group, glucose does not give Schiff test and 2,4-DNP test
• B. Glucose does not react with sodium hydrogen sulphite to form addition product
• C. The pentaacetate of glucose does not react with hydroxyl amine showing the absence of free $-CHO$ group
• D. None of above

Answer 1

Answer: (A), (B), (C)

The pentaacetate of glucose does not react with hydroxyl amine showing the absence of free $-CHO$ group

The above behavior could not be explained by the open chain structure. Because one of the $-OH$ groups of glucose 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. This explains the absence of $-CHO$ group.