Question

What is the difference between an enantiomer and a diastereomer?

Answer 1

An enantiomer is the non-superimposable mirror image of another. A diastereomer can have one or more (but not all) different stereocenters.

From this definition, we can see that the "not all different stereocenters" specification is the differentiating factor between a diastereomer and an enantiomer. It's easier to see with a picture.

• D-threose and L-threose are enantiomers since they are non-superimposable and are reflections of each other.

• D-erythrose and L-erythrose simply have their `alpha` carbon's `"OH"` and `"H"` nudged to switch the configuration, relative to D-threose and L-threose, respectively.