[dahy-uh-ster-ee-uh-mer, -steer-]
noun Chemistry.
either of a pair of stereoisomers that are not mirror images of each other.
Also called diastereoisomer [dahy-uh-ster-ee-oh-ahy-suh-mer, -steer-] .
Compare enantiomer.

1935–40; dia- + stereo(iso)mer

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World English Dictionary
diastereoisomer (ˌdaɪəˌstɛrɪəʊˈaɪsəmə)
chem a type of isomer that differs in the spatial arrangement of atoms in the molecule, but is not a mirror image; a stereoisomer that is not an enantiomer

Collins English Dictionary - Complete & Unabridged 10th Edition
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Encyclopedia Britannica


either member of a pair of substances that differ with respect to the configurations of their molecules (i.e., stereoisomers) and that lack a mirror-image relationship (i.e., are not enantiomorphs). An example is the pair consisting of either of the two optically active forms of tartaric acid (either the dextrorotatory or levorotatory form) and the optically inactive meso form of the same acid (mesotartaric acid). Unlike enantiomorphs, diastereoisomers need not have closely similar physical and chemical properties: they may differ as greatly as do structural isomers. For example, either of the optically active tartaric acids melts at 187 C (369 F), whereas mesotartaric acid melts at 143 C (290 F)

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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