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
Oct 30, 2014

The eight aldopentoses are shown below.


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