What does diastereoisomer mean?
A diastereoisomer is a type of stereoisomer: a compound sharing another's molecular formula and atom-to-atom bonding order, but differing in the three-dimensional arrangement of those atoms without being that compound's mirror image. Where enantiomers exist only in matched pairs of left- and right-handed forms, diastereoisomers can occur in larger sets, because molecules with several asymmetric centres may vary independently at each one. Crucially, diastereoisomers usually differ measurably in physical properties — melting point, solubility, boiling point, and reactivity — which makes them separable by conventional techniques such as crystallization or distillation. This distinguishes them from enantiomers, whose identical physical properties demand special chiral methods to resolve. Diastereoisomerism matters enormously in pharmaceutical science, since different forms of the same molecule can show dramatically different biological activity and safety profiles. Chemists also use the adjective form, diastereomeric, as in 'diastereomeric excess', a key measure of selectivity in synthetic reactions.
nounA stereoisomer that is not an enantiomer — one of two or more compounds having the same molecular formula and sequence of bonded atoms but differing in the spatial arrangement of atoms in a way not related as mirror images.
- One of a set of stereoisomers of a compound that are not mirror images (enantiomers) of each other; stereoisomers differing in configuration at some, but not all, of their stereocentres.
"The two diastereoisomers of the drug differ sharply in biological activity, so only one is approved for clinical use."
"Because the diastereoisomers have different physical properties such as melting point and solubility, they can often be separated by ordinary crystallization rather than chiral chromatography."
"In carbohydrate chemistry, glucose and galactose are classic diastereoisomers, differing in the configuration at only one of their several stereocentres."
Standard English plural; used when referring to multiple such compounds collectively or to a set of stereoisomers.
"The synthesis produced four diastereoisomers, which were separated by column chromatography."
Two diastereoisomers can share every chemical formula yet behave like entirely different drugs — thalidomide taught chemistry this lesson tragically, with one form sedating patients and its mirror-related partner causing severe birth defects.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of diastereoisomer
The word combines three elements of Greek origin: 'dia-' meaning 'through' or 'apart', 'stereo-' from Greek 'stereos' meaning 'solid', and 'isomer', itself from 'isos' ('equal') and 'meros' ('part'). It arose in late 19th-century chemistry alongside the development of stereochemistry by Jacobus van't Hoff and Joseph Le Bel, who established that molecular geometry determines properties. The shorter variant 'diastereomer' followed the same pattern seen in 'enantiomer'. Cognates sharing these roots include 'isotope', 'polymer', and 'stereoscopic'.
Related word forms
How diastereoisomer is actually used
Diastereoisomer is a technical term confined to chemistry and closely related sciences. The shortened form 'diastereomer' is now more frequent in modern usage, though both are fully standard. It is used almost exclusively in formal, scientific writing and is rarely encountered outside laboratory, academic, or pharmaceutical contexts.
Easily confused with diastereoisomer
Enantiomers are stereoisomers that are non-superimposable mirror images of each other, whereas diastereoisomers are stereoisomers that are NOT mirror images.
Conformers are stereoisomers interconvertible by rotation about single bonds, while diastereoisomers require bond-breaking to interconvert.