The structure of a disaccharide is shown below. Which statement applies?

• A. Both sugar rings A and B are in equilibrium with their linear chain forms.
• B. Only sugar ring A is in equilibrium with its linear chain form.
• C. Only sugar ring B is in equilibrium with its linear chain form.
• D. Neither sugar ring is in equilibrium with their linear chain form.
• E. None of the above statements are correct.

Answer: (C)

Verified step by step guidance

1. Identify the two sugar rings in the disaccharide structure. The left ring is sugar ring A, and the right ring is sugar ring B.
2. Determine the type of glycosidic bond present between the two sugar rings. The bond is an O-glycosidic bond connecting the anomeric carbon of sugar ring A to the oxygen of sugar ring B.
3. Analyze the anomeric carbon of each sugar ring. The anomeric carbon is the carbon attached to two oxygen atoms, one in the ring and one in the glycosidic bond.
4. For sugar ring A, the anomeric carbon is involved in the glycosidic bond, which means it is not free to equilibrate with its linear form. Therefore, sugar ring A is not in equilibrium with its linear chain form.
5. For sugar ring B, the anomeric carbon is not involved in the glycosidic bond, allowing it to potentially open to its linear form. Therefore, sugar ring B is in equilibrium with its linear chain form.