The question asks for the C-2 epimer of D-glucose. In carbohydrate chemistry, epimers are pairs of monosaccharides that differ only at one chiral center. To solve this, we need to identify the C-2 epimer of D-glucose from the given options. Let's go through each option:
D-Glucose: The structure of D-glucose is: \(\text{H--(C=O)--(CHOH)--(CHOH)--(CHOH)--CH}_2\text{OH}\) But C-2 epimer of D-glucose would have a different configuration at the C-2 chiral center.
D-Mannose: D-Mannose is the C-2 epimer of D-glucose. In the Fischer projection, D-mannose has the hydroxyl group on the left side at the C-2 position, which is opposite to the configuration in D-glucose. Hence, the correct answer is D-Mannose.
D-Fructose: D-fructose is a ketohexose and not an epimer of D-glucose as it differs at the carbonyl group (C=O position).
D-Galactose: D-Galactose differs from D-glucose at the C-4 position, not the C-2 position, so it is not the C-2 epimer of D-glucose.
Therefore, the C-2 epimer of D-glucose is D-Mannose.
