Which of the following reactions is not explained by the open chain structure of glucose?
Show Hint
- Glucose on prolonged heating with HI forms n-hexane.
- Glucose reacts with hydroxylamine to form an oxime.
- Glucose gets oxidized to gluconic acid on reaction with bromine water.
- Glucose exists in two different crystalline forms, alpha ($\alpha$) and beta ($\beta$).
The Correct Option is D
Solution and Explanation
The open-chain Fischer projection of D-glucose correctly predicts many of its chemical properties, but fails to explain certain anomalous behaviors.
Step 2: Meaning
Reactions that prove the straight carbon chain, the aldehyde group, and the alcohol groups are all supported by the open-chain structure.
Step 3: Analysis
Option (A) confirms the straight 6-carbon chain.
Options (B) and (C) confirm the presence of an active, free aldehyde group.
However, the existence of D-glucose in two distinct crystalline isomeric forms ($\alpha$-D-glucose
and $\beta$-D-glucose, called anomers) stems entirely from the creation of a new chiral center at C-1 when the molecule folds into a closed, cyclic hemiacetal ring structure.
Step 4: Conclusion
The open-chain structure cannot possibly account for the existence of these two separate anomeric forms.
Final Answer: (D)
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