Diastereomer

A stereoisomer that is not a mirror image of another stereoisomer. Diastereomers differ in configuration at one or more, but not all, corresponding stereogenic elements.

Stereoisomerism: A form of isomerism in which molecules share connectivity but differ in spatial arrangement. Diastereomers belong to this broader class of molecules with different spatial arrangements.
Enantiomer: One of a pair of stereoisomers that are non-superimposable mirror images of each other. Unlike enantiomers, diastereomers are not mirror-image partners.
Diastereomeric resolution: A method for separating enantiomers by converting them into diastereomeric derivatives or salts. Different properties of the resulting diastereomers make separation possible.
Tartaric acid: A dicarboxylic acid with two stereogenic centers that occurs in distinct stereoisomeric forms. Its chiral and meso forms illustrate diastereomerism within one molecular framework.
Stereogenic center: An atom at which exchanging two attached groups produces a stereoisomer. Different configurations at corresponding stereogenic centers can distinguish diastereomers.
Constitutional isomer: A compound with the same molecular formula as another compound but different atom connectivity. Diastereomers retain the same connectivity, unlike constitutional isomers.
Chiral resolution: The separation of enantiomers into their individual forms. Diastereomer formation is a classical route to resolving a racemic mixture.
Threose: An aldotetrose sugar with two stereogenic centers and four possible stereoisomers. Its configurations provide a compact example of multiple diastereomeric sugar forms.
Absolute configuration: The three-dimensional arrangement of groups around a stereogenic element, commonly designated R or S. Comparing configurations identifies which stereogenic centers differ between two structures.
Epimer: A diastereomer that differs from another molecule at exactly one stereogenic center. Epimers are the specific case in which only one stereogenic center changes.

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