In chemistry, epimers are diastereomers that differ in configuration of only one stereogenic center. Diastereomers are a class of stereoisomers that are non-superimposable, non-mirror images of one another, unlike enantiomers which are non-superimposable mirror images of one another. [March, Jerry and Smith, Michael B.. March's Advanced Organic Chemistry: "Reactions, Mechanisms and Structure". "6th ed." Hoboken, NJ: John Wiley & Sons, Inc., 2007.]

For example, the sugars α-glucose and β-glucose are epimers. In α-glucose, the -OH group on the first (anomeric) carbon is in the direction opposite the methylene group (in the axial position). In β-glucose, the -OH group is oriented in the same direction as the methylene group (in the equatorial position). [ [http://www.biotopics.co.uk/as/glucose2.html Structure of the glucose molecule ] ] These two molecules are both epimers and anomers.

In this case, β-D-glucopyranose and β-D-mannopyranose are epimers because they differ only in the stereochemistry at the 2 position. The hydroxyl group in β-D-glucopyranose is equatorial (in the "plane" of the ring) while in β-D-mannopyranose the 2 hydroxyl group is axial (up from the "plane" of the ring). These two molecules are epimers but not anomers.

In chemical nomenclature, one of the epimeric pairs is given the prefix epi- for example in quinine and "epi-quinine". When the pairs are enantiomers, the prefix becomes ent-.


External links

* IUPAC Gold Book [http://www.iupac.org/goldbook/E02167.pdf definition]

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  • epimer — EPIMÉR s.m. (chim.) Fiecare dintre cei doi izomeri ai unei monozaharide. [< fr. épimère]. Trimis de LauraGellner, 13.09.2007. Sursa: DN  EPIMÉR s. m. fiecare dintre cei doi izomeri ai unei monozaharide, care diferă între ei prin configuraţia… …   Dicționar Român

  • Epimer — Als Epimer bezeichnet man in der Chemie: ein Paar von Diastereoisomeren eines Moleküls, siehe Isomerie#Diastereomerie in der Biologie: eine Platte des Chitinskeletts der Gliederfüßer Diese Seite ist eine Begriffsklä …   Deutsch Wikipedia

  • epimer — noun Etymology: epi + isomer Date: circa 1911 either of two stereoisomers that differ in the arrangement of groups on a single asymmetric carbon atom (as the first chiral center of a sugar s carbon chain) • epimeric adjective …   New Collegiate Dictionary

  • epimer — Diastereomeric monosaccharides that have opposite configurations of a hydroxyl group at only one position, eg. D glucose and D mannose …   Dictionary of molecular biology

  • epimer — epimeric /ep euh mer ik/, adj. /ep euh meuhr/, n. Chem. either of a pair of isomeric aldose compounds, esp. of certain sugars, that differ from each other in the positions of the H and OH at the second atom from the end of the carbon chain, as d… …   Universalium

  • epimer — noun any diastereoisomer that has the opposite configuration at only one of the stereogenic centres …   Wiktionary

  • epimer — One of two molecules (having more than one chiral center) differing only in the spatial arrangement about a single chiral atom; e.g., α d glucose and α d galactose (with respect to carbon 4). See sugars. Cf.:anomer. [epi + G. meros, part] * * *… …   Medical dictionary

  • Epimer — E|pi|mer [Kurzw. aus ↑ epi (2) u. ↑ Isomer], das; s, e, fachspr. auch: E|pi|me|re, das; n, n: Bez. für diastereoisomere Verb. (↑ Diastereoisomerie), die an einem von zwei oder mehreren ↑ asymmetrischen Atomen (Chiralitätszentren) eine… …   Universal-Lexikon

  • epimer — n. type of aldose compound (Chemistry) …   English contemporary dictionary

  • epimer — [ ɛpɪmə] noun Chemistry each of two isomers with different configurations of atoms about one of several asymmetric carbon atoms present. Derivatives epimeric mɛrɪk adjective epimerism ɪ pɪm , ɛ noun …   English new terms dictionary

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