Diastereomere

A diastereomere, also spelled diastereomere in some languages, is a type of stereoisomer that is not the mirror image of another stereoisomer. Diastereomers share the same carbon skeleton and the same set of stereogenic centers, but differ in configuration at one or more of these centers while not being related as mirror images. When a molecule has n stereocenters, there can be up to 2^n stereoisomers; among them, some form enantiomeric pairs, while the remaining isomers are diastereomeric with respect to one another.

An often-cited example is 2,3-dibromobutane. The (R,R) and (S,S) forms are enantiomers, whereas the (R,S) form is a diastereomer of both. Diastereomerism is also encountered in geometric isomers such as cis/trans relationships in substituted rings; these are diastereomers relative to each other.

Diastereomers typically have different physical properties, such as melting points and solubilities, and can display different reactivities and biological activities. In contrast to enantiomers, which have identical physical properties in achiral environments, diastereomers usually behave differently in chemical and biological contexts. Determining diastereomerism is essential in fields like organic synthesis and pharmaceuticals, where the separation and selective formation of a preferred diastereomer can be important for activity and safety.