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

The question asks which reaction is not explained by the open-chain structure of glucose. To determine the correct answer, let's consider each option:

1. Glucose on prolonged heating with HI forms n-hexane: This reaction suggests that glucose contains a six-carbon chain. This outcome aligns well with the open-chain structure of glucose where each carbon is part of the chain contributing to n-hexane formation.
2. Glucose reacts with hydroxylamine to form an oxime: The formation of an oxime confirms the presence of an aldehyde group (-CHO) in the glucose molecule. This reaction can also be explained by the open-chain structure of glucose since it exposes the aldehyde group.
3. Glucose gets oxidized to gluconic acid on reaction with bromine water: This reaction involves the oxidation of the aldehydic group to the carboxylic acid group, producing gluconic acid. This process is supported by the open-chain form of glucose where the aldehyde group is accessible for oxidation.
4. Glucose exists in two different crystalline forms, alpha (α) and beta (β): This is a characteristic of glucose that is explained by its cyclic (hemiacetal) forms rather than the open-chain form. The two different forms (α and β) result from the different orientations of the -OH group at the anomeric carbon in the cyclic structures, not by any feature of the open-chain structure.

Therefore, the reaction or phenomenon not explained by the open-chain structure of glucose is the existence of glucose in two different crystalline forms, alpha (α) and beta (β).