When are epimers called diastereomers?

1 Answer
Ernest Z.
Sep 25, 2015

Epimers are always diastereomers.

Explanation:

**Diastereomers ** are compounds that contain two or more chiral centres and are not mirror images of each other.

For example, the aldopentoses each contain three chiral centres.

Thus, D-ribose is a diastereomer of D-arabinose, D-xylose, and D-lyxose.

chemistry2.csudh.edu

Epimers are diastereomers that contain more than one chiral center but differ from each other in the absolute configuration at only one chiral center.

Thus, D-ribose and D-arabinose are epimers (and diastereomers), because they differ in configuration only at "C-2"C-2.

D-ribose and D-xylose are epimers (and diastereomers), because they differ in configuration only at "C-3"C-3.

D-ribose and D-lyxose diastereomers, but they are not epimers, because they differ in configuration at both "C-2"C-2 and "C-3"C-3.

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