Question

Which of the following reactions is not explained by the open chain structure of glucose?

• A. Glucose on prolonged heating with HI forms n-hexane.
• B. Glucose reacts with hydroxylamine to form an oxime.
• C. Glucose gets oxidized to gluconic acid on reaction with bromine water.
• D. Glucose exists in two different crystalline forms, alpha ($\alpha$) and beta ($\beta$).

Hint:

Open-chain glucose explains aldehyde reactions. Cyclic glucose explains anomers ($\alpha$ and $\beta$ forms) and mutarotation.

Answer 1

The Correct Option is D

Concept: Glucose exists in both open-chain and cyclic (ring) forms. The open-chain structure explains reactions involving the aldehyde group (–CHO), while cyclic structure explains stereoisomerism like $\alpha$ and $\beta$ forms.
Step 1: Check which reactions are explained by open-chain structure.
Option (A): Formation of n-hexane with HI shows presence of straight carbon chain. Explained by open-chain structure.
Option (B): Reaction with hydroxylamine forming oxime indicates presence of aldehyde group. Explained by open-chain structure.
Option (C): Oxidation to gluconic acid with bromine water confirms aldehyde group. Explained by open-chain structure.
Option (D): Existence of $\alpha$ and $\beta$ forms arises due to cyclic hemiacetal ring structure and anomerism. Not explained by open-chain structure.