Question

What are the correct structural descriptions for M and N?

• A. M is \(\alpha\)-D-(+)-glucopyranose and N is \(\beta\)-D-(\(-\))-fructofuranose
• B. M is \(\beta\)-D-(+)-glucopyranose and N is \(\beta\)-D-(\(-\))-fructofuranose
• C. M is \(\alpha\)-D-(+)-glucopyranose and N is \(\alpha\)-D-(\(-\))-fructofuranose
• D. M is \(\alpha\)-D-(+)-glucofuranose and N is \(\beta\)-D-(\(-\))-fructopyranose

Hint:

Remember a simple visual trick for Haworth projections of D-sugars:
- Down is \(\alpha\) (like 'A' for Alpha points down).
- Up is \(\beta\) (like 'B' for Beta points up).
This mnemonic helps you identify anomers in a fraction of a second.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the correct chemical names and stereochemical configurations of the two carbohydrate structures labeled \(\text{M}\) and \(\text{N}\), represented as Haworth projections.

Step 2: Key Formula or Approach:
To classify the carbohydrate structures in Haworth projections:
1. Count the ring size: A 6-membered ring containing oxygen is a pyranose, and a 5-membered ring containing oxygen is a furanose.
2. Identify the monomer: Glucose forms a pyranose ring (glucopyranose), whereas Fructose forms a furanose ring (fructofuranose).
3. Determine the anomeric configuration (\(\alpha\) or \(\beta\)):
- For D-sugars, if the hemiacetal hydroxyl group (\(-\text{OH}\)) on the anomeric carbon points downwards (trans to the terminal \(-\text{CH}_2\text{OH}\) group), it is the \(\alpha\)-anomer.
- If the hydroxyl group points upwards (cis to the terminal \(-\text{CH}_2\text{OH}\) group), it is the \(\beta\)-anomer.

Step 3: Detailed Explanation:
- Analyzing Structure M:
- Ring size: 6-membered ring containing oxygen, indicating a pyranose ring of D-glucose.
- Anomeric carbon (C1, rightmost carbon): The hydroxyl group (\(-\text{OH}\)) is pointing downwards.
- Since the anomeric \(-\text{OH}\) is down, it is the \(\alpha\)-anomer.
- Therefore, \(\text{M}\) is \(\alpha\)-D-(+)-glucopyranose.
- Analyzing Structure N:
- Ring size: 5-membered ring containing oxygen, indicating a furanose ring of D-fructose.
- Anomeric carbon (C2, rightmost carbon): The hydroxyl group (\(-\text{OH}\)) is pointing upwards, and the \(-\text{CH}_2\text{OH}\) group is pointing downwards.
- Since the anomeric \(-\text{OH}\) is up, it is the \(\beta\)-anomer.
- Therefore, \(\text{N}\) is \(\beta\)-D-(\(-\))-fructofuranose.

Step 4: Final Answer:
Thus, \(\text{M}\) is \(\alpha\)-D-(+)-glucopyranose and \(\text{N}\) is \(\beta\)-D-(\(-\))-fructofuranose, which corresponds to option (A).