Home > Organic Chemistry > Diastereomers

When are epimers called diastereomers?

Answer 1

Epimers are always diastereomers.

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.

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"#.

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

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

By signing up, you agree to our Terms of Service and Privacy Policy

Answer 2

Sarah Angotti

Epimers are called diastereomers when they have more than one chiral center and differ in configuration at some, but not all, of these chiral centers.

By signing up, you agree to our Terms of Service and Privacy Policy

Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.