Question

The correct representation in six-membered pyranose form for the following sugar $ [X]$ is 

• A.
• B.
• C.
• D.

Hint:

To identify- and-anomers, check the orientation of the-OH group on the anomeric carbon. In-anomers, it points downward, while in-anomers, it points upward

Answer 1

The Correct Option is A

The question requires identifying the correct pyranose form of a given sugar. The structure shown in the image is the Fischer projection of an aldohexose. To convert this into its pyranose form, we need to follow these steps:

1. Identify the sugar given; in this case, it's likely a D-glucose based on the arrangement of the hydroxyl (OH) groups.
2. Pyranose forms result from the reaction between an aldehyde group and an alcohol group on the sugar itself, creating a hemiacetal. For glucose, the C-1 aldehyde reacts with the C-5 hydroxyl group.
3. In the six-membered pyranose ring, the oxygen becomes a part of the ring, forming a six-membered ring system.
4. The arrangement of the OH groups in the linear form determines the orientation in the ring form. In D-glucose:
   • C-1 (anomeric carbon) hydroxyl group will point either upwards (β-anomer) or downwards (α-anomer).
   • The OH on C-2, C-3, and C-4 decide whether they are up or down compared to the ring plane, helping confirm the correct stereochemistry.
5. From the options provided, choose the structure that matches this stereochemical orientation.

Upon examining the structures, the correct pyranose form of the sugar $[X]$ is represented by the following image:

This structure correctly aligns with the Fischer projection, specifically showing the hydroxyl groups in the axial and equatorial positions as derived from the Fischer projection of D-glucose.