Question

Identify pair of C₄ epimers:

• A. D-glucose and D-galactose
• B. D-glucose and D-fructose
• C. D-glucose and D-mannose
• D. D-glucose and D-xylulose

Answer 1

The Correct Option is A

To identify a pair of C₄ epimers, we need to understand what epimers are in the context of carbohydrate chemistry. Epimers are carbohydrates that differ in configuration around only one specific carbon atom (except for the reference carbon that defines the D or L configuration in Fischer projections).

When it comes to C₄ epimers, this difference occurs on the fourth carbon atom in the sugar. Let's analyze the given options:

1. D-glucose and D-galactose: These are indeed C₄ epimers. The configuration around the fourth carbon atom differs between these two sugars. Specifically, the hydroxyl (-OH) group on the fourth carbon is oriented differently in D-glucose and D-galactose. In D-glucose, the hydroxyl group on C₄ is on the right, while in D-galactose, it is on the left (in the standard Fischer projection of the sugars).
2. D-glucose and D-fructose: These are not epimers. D-glucose is an aldohexose, whereas D-fructose is a ketohexose. This means they differ in much more than just one carbon configuration.
3. D-glucose and D-mannose: These are C₂ epimers, not C₄. The difference in configuration occurs at the second carbon atom.
4. D-glucose and D-xylulose: These are not epimers, as they belong to different categories of carbohydrates. D-glucose is an aldohexose, whereas D-xylulose is a ketopentose.

Thus, the correct answer is that D-glucose and D-galactose are C₄ epimers.

Therefore, the correct choice is recognized from the differences in their chemical structure based on epimer definition:

• D-glucose and D-galactose are C₄ epimers.