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BIO NMDCAT Carbohydrates
nmdcat.online June 27, 2026

The formation of a cyclic hemiacetal in glucose involves the reaction of the aldehyde carbon (C1) with the hydroxyl group of C5, forming a six-membered pyranose ring. If the ring closure involved the C4 hydroxyl instead, it would form a

A. Five-membered furanose ring
✓
B. Seven-membered ring
C. Linear extended chain
D. Double ring structure

📝 Explanation

The size of the ring is determined by which hydroxyl attacks the carbonyl. Reaction with the C4-OH forms a five-membered ring (furanose). Reaction with the C5-OH forms a six-membered ring (pyranose). The pyranose form is favored for most aldohexoses due to lower steric strain.

📖 Additional Information

  • Five-membered furanose ring
  • Seven-membered ring
  • Linear extended chain
  • Double ring structure

The size of the ring is determined by which hydroxyl attacks the carbonyl. Reaction with the C4-OH forms a five-membered ring (furanose). Reaction with the C5-OH forms a six-membered ring (pyranose). The pyranose form is favored for most aldohexoses due to lower steric strain.

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