The term epimer is used to describe diastereomers that differ in the configuration about a single carbon atom. Which pairs of the eight possible aldopentoses are epimers?
1 Answer
The eight aldopentoses are shown below.
Explanation:
Note: The configurations at C-4 of L-xylose and L-lyxose should be HO-C-H.
Each aldopentoses has three stereocentres, so each will have three epimers.
For each aldopentose, the epimers at C-2, C-3, and C-4 are:
- D-ribose: D-arabinose, D-xylose, and L-lyxose
- D-arabinose: D-ribose, D-lyxose, and L-xylose
- D-xylose: D-lyxose, D-ribose, and L-arabinose
- D-lyxose: D-xylose, D-arabinose, and L-ribose
- L-ribose: L-arabinose, L-xylose, and D-lyxose
- L-arabinose: L-ribose, L-lyxose, and D-xylose
- L-xylose: L-lyxose, L-ribose, and D-arabinose
- L-lyxose: L-xylose, L-arabinose, and D-ribose
