Question

Which of the following pair is C2-epimer?

• A. D-Glucose, D-Arabinose
• B. D-Glucose, D-Maltose
• C. D-Allose, D-Ribose
• D. D-Glucose, D-Mannose

Answer 1

The correct option is D

D-Glucose, D-Mannose

Explanation of correct option

(D)D-Glucose, D-Mannose

C2 Epimer:

• Epimers are diastereomers with one or more chiral carbons in their structures but only one chiral carbon that varies in configuration.
• Let's take a look at the structure of D-Glucose.
• The carbon chain is given numbers based on the priority of the functional groups.
• The elements are exchanged from right to left to left to right in the $\mathrm{C}2$ position.
• D-Mannose is the result of this process.

• From $\mathrm{C}2\mathrm{to}\mathrm{C}5$, all chiral carbons have the same configuration: 2R, 3S, 4R, and 5R.
• However, its epimer D-Mannose has a different arrangement at $\mathrm{C}2$, and all of D-chiral Mannose's carbons are arranged as 2S, 3S, 4R, and 5R.
• As a result, we term them epimers since just the $\mathrm{C}2$ location varies, while the rest is similar.

Explanation of incorrect options:

• D-Arabinose, on the other hand, only comprises a five-carbon chain.
• 
• D-Maltose is distinct from D-Glucose because it contains two D-glucopyranose units.
• D-allose is six-carbon, and D-ribose is a five-carbon chain.
• 
• Therefore, the options A, B, and C are incorrect.

Hence, option (D) is correct. D-Glucose, D-Mannose are C2 epimer.