Organic Chemistry And Reaction Mechanisms Codexery

Enantiomer

Mirror-image molecules that are non-superposable and rotate polarized light.

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An enantiomer is one of a pair of molecular entities that are non-superposable mirror images of each other, like right and left hands.[1][2] Enantiomers rotate plane-polarized light in opposite directions, and a racemic mixture of equal amounts does not rotate light.[3] Stereoisomers that are non-superposable mirror images are enantiomers, while those that are non-superposable but not mirror images are diastereomers.[4]

Last updated 2026-10-18 from the source article.

Quick Facts

Field
Chemistry
Known for
  • Chirality
  • optical isomerism
  • and the R/S (+)/(-)
  • and D/L naming conventions
Related terms
  • Racemic mixture
  • diastereomer
  • chirality center

Facts from the source article.

Key facts and history

The R/S system assigns priority to groups around a chiral center based on atomic number, with the highest atomic number getting highest priority.[5] The (+) or (−) symbol indicates the direction of optical rotation: dextrorotatory rotates light clockwise, levorotatory rotates it counterclockwise.[6] The prefix ar- (from Latin recto, right) and es- (from Latin sinister, left) are applied to right- and left-handed versions, as in arketamine and esketamine.[7] The sedative thalidomide, sold from 1957 until 1961, was withdrawn when found to cause birth defects.[8]

Enantiopure compounds consist of only one enantiomer and can have improved therapeutic efficacy, a switch called a chiral switch.[9] A stereocenter that is an asymmetric atom is referred to as a chirality center.[10][11] Whenever a compound possesses exactly one asymmetric atom, or any odd number of them, chirality is guaranteed.[12]

What the research sources say

The Dictionary.com entry notes that enantiomers usually behave the same chemically but differ in optical behavior and sometimes in how quickly they react with other enantiomers.[13] The same source states that selecting the correct enantiomer can be essential because two mirror-image versions of the same molecule may have very different biological or medical effects.[13] That resource also describes the R/S system, where the path curving clockwise gives the rectus (R) enantiomer and counterclockwise gives the sinister (S) enantiomer.[14] Theoretical physics predicts a minute energy difference between enantiomers due to parity violation of the weak nuclear force, on the order of 10⁻¹² eV.[15]

References

  1. Wikipedia, "Enantiomer" (CC BY-SA 4.0), which cites: "Enantiomer: Definition & Meaning", Dictionary.com; Chemistry (IUPAC), "IUPAC - optical isomers (O04308)", goldbook.iupac.org; Chemistry (IUPAC), "IUPAC - antipodes (A00403)", goldbook.iupac.org; Chemistry (IUPAC), "IUPAC - optical antipodes (O04304)", goldbook.iupac.org (we also read that source) en.wikipedia.org
  2. Wikipedia, "Enantiomer" (CC BY-SA 4.0), which cites: McConathy, "Stereochemistry in Drug Action", Primary Care Companion to the Journal of Clinical Psychiatry, 2003, p. 70–73 (original not read by us) en.wikipedia.org
  3. Wikipedia, "Enantiomer" (CC BY-SA 4.0), which cites: "Chirality and Optical Activity", chemed.chem.purdue.edu; Chemistry (IUPAC), "IUPAC - racemic (R05026)", goldbook.iupac.org; Chemistry (IUPAC), "IUPAC - racemate (R05025)", goldbook.iupac.org; Weber, "Library Guides: CHEM 221: Stereochemistry / Isomerism", libraryguides.salisbury.edu (we also read that source) en.wikipedia.org
  4. Wikipedia, "Enantiomer" (CC BY-SA 4.0) en.wikipedia.org
  5. Wikipedia, "Enantiomer" (CC BY-SA 4.0), which cites: Brewster, "The distinction of diastereomers in the Cahn-Ingold-Prelog (RS) notation", The Journal of Organic Chemistry, December 1986, p. 4751–4753 (we also read that source) en.wikipedia.org
  6. Wikipedia, "Enantiomer" (CC BY-SA 4.0), which cites: Caldwell, "Stereochemistry: definitions and a note on nomenclature", Human Psychopharmacology: Clinical and Experimental, December 2001, p. S105–S107; Brewster, "The distinction of diastereomers in the Cahn-Ingold-Prelog (RS) notation", The Journal of Organic Chemistry, December 1986, p. 4751–4753; Brewster, "The distinction of diastereomers in the Cahn-Ingold-Prelog (RS) notation", The Journal of Organic Chemistry, December 1986, p. 4751–4753 (we also read that source) en.wikipedia.org
  7. Wikipedia, "Enantiomer" (CC BY-SA 4.0), which cites: Long, "Evaluation of Trials Comparing Single-Enantiomer Drugs to Their Racemic Precursors: A Systematic Review", JAMA Network Open, May 6, 2021, p. e215731 (original not read by us) en.wikipedia.org
  8. Wikipedia, "Enantiomer" (CC BY-SA 4.0), which cites: Knoche, "Investigations on the in vitro racemization of thalidomide by high-performance liquid chromatography", Journal of Chromatography A, 1994, p. 235–240; Voet, "Fundamentals of Biochemistry", Wiley, 2006, p. 89 (we also read that source) en.wikipedia.org
  9. Wikipedia, "Enantiomer" (CC BY-SA 4.0), which cites: Ariëns, "Stereochemistry: A source of problems in medicinal chemistry", Medicinal Research Reviews, 1986, p. 451–466 (original not read by us) en.wikipedia.org
  10. Wikipedia, "Enantiomer" (CC BY-SA 4.0), which cites: ; Wade, "Precision in Stereochemical Terminology", J. Chem. Educ., 2006, p. 1793 (original not read by us) en.wikipedia.org
  11. Wikipedia, "Enantiomer" (CC BY-SA 4.0), which cites: Karras, ""Synthesis of Enantiomerically Pure Helical Aromatics Such As NHC Ligands and Their Use in Asymmetric Catalysis", Charles University, 2018; Eliel, "Stereochemistry of organic compounds", Wiley, 1994; Clayden, "Organic chemistry", Oxford University Press, 2012; ; Karras, ""Synthesis of Enantiomerically Pure Helical Aromatics Such As NHC Ligands and Their Use in Asymmetric Catalysis", Charles University, 2018; Clayden, "Organic chemistry", Oxford University Press, 2012; Clark, "Introduction to stereochemistry", 2021; Wade, "Precision en.wikipedia.org
  12. Wikipedia, "Enantiomer" (CC BY-SA 4.0), which cites: Karras, ""Synthesis of Enantiomerically Pure Helical Aromatics Such As NHC Ligands and Their Use in Asymmetric Catalysis", Charles University, 2018 (we also read that source) en.wikipedia.org
  13. "Enantiomer: Definition & Meaning", Dictionary.com. facts only, no text reused. dictionary.com
  14. "Chirality and Optical Activity", chemed.chem.purdue.edu. facts only, no text reused. chemed.chem.purdue.edu
  15. Wikipedia, "Enantiomer" (CC BY-SA 4.0), which cites: Eliel, "Stereochemistry of organic compounds", Wiley, 1994; Albert, "The origin of chirality in the molecules of life: a revision from awareness to the current theories and perspectives of this unsolved problem", Royal Society of Chemistry, 2008; Stickler, "Enantiomer Superpositions from Matter-Wave Interference of Chiral Molecules", Physical Review X, 2021-09-14; Eliel, "Stereochemistry of organic compounds", Wiley, 1994 (we also read that source) en.wikipedia.org

Each numbered sentence above was checked against the source it cites before publication. Sentences citing Wikipedia adapt text from the English Wikipedia article Enantiomer (contributors), used under CC BY-SA 4.0; this entry is available under the same licence. Other sources were used for facts only; no text or images are copied from them.

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Sources

Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.

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