In chemistry, enantiomers (from the Greek ἐνάντιος, opposite, and μέρος, part or portion) are stereoisomers that are nonsuperimposable complete mirror images of each other, much as one's left and right hands are "the same" but opposite. Image File history File links Size of this preview: 800 × 266 pixelsFull resolution (866 × 288 pixel, file size: 7 KB, MIME type: image/png) I made this in ChemDraw. ... Chemistry - the study of atoms, made of nuclei (conglomeration of center particles) and electrons (outer particles), and the structures they form. ... Stereoisomerism is the arrangement of atoms in molecules whose connectivity remains the same but their arrangement in space is different in each isomer. ... Superimposition is a graphics term meaning the placement of an image or video on top of an already-existing image or video, usually to add to the overall image effect, but also sometimes to conceal something (such as when a different face is superimposed over the original face in a... A mirror image is a mirror based duplicate of a single image. ... The term chiral (pronounced ) is used to describe an object which is non-superimposable on its mirror image. ...

Enantiomers have, when present in a symmetric environment, identical chemical and physical properties except for their ability to rotate plane-polarized light by equal amounts but in opposite directions. A mixture of equal parts of an optically active isomer and its enantiomer is termed racemic and has a net rotation of plane-polarized light of zero. Two intersecting planes in three-dimensional space In mathematics, a plane is a two-dimensional manifold or surface that is perfectly flat. ... This article treats polarization in electrodynamics. ... In chemistry, a racemate is a mixture of equal amounts of left- and right-handed stereoisomers of a chiral molecule. ... This article treats polarization in electrodynamics. ...

Two symmetrical enantiomers often do have different chemical properties related to other substances that are also enantiomers. Since many molecules in the bodies of living beings are enantiomers themselves, there is often a marked difference in the effects of two symmetrical enantiomers on living beings, including humans.

Naming conventions

Main article: Optical isomerism

There are several conventions used for naming chiral compounds, all displayed as a prefix before the chemical name of the substance: Optical isomerism is a form of isomerism (specifically stereoisomerism) where the two different isomers are the same in every way except being non-superposable mirror images of each other. ... The term chiral (pronounced ) is used to describe an object which is non-superimposable on its mirror image. ...

• (+)- versus (−)-; also written d- vs. l-

- based on the substance's ability to rotate polarized light.

• D- vs. L-

- based on the actual geometry of each enantiomer, with the version synthesized from naturally occurring (+)-glyceraldehyde being considered the D- form. Fischer projection of D-glyceraldehyde Glyceraldehyde is a triose monosaccharide with chemical formula C3H6O3. ...

• (R)- vs. (S)-

- based on the actual geometry of each enantiomer, using the Cahn-Ingold-Prelog priority rules to classify the form. Molecules with multiple stereogenic centers will have a corresponding number of letters; e.g. natural (+)-α-tocopherol is R,R,R-α-tocopherol. To meet Wikipedias quality standards, this article may require cleanup. ... A stereocenter is a carbon atom in a chemical compound that has four different types of atoms or groups of atoms attached to each side of it. ...

The (+)- vs. (−)- convention is the only one based on optical properties. The other two conventions are based on the actual geometry of each enantiomer. There is no correspondence between any convention. In nature, many chiral substances are only produced in one optical form, while (most) man-made chiral substances are racemic mixtures. the purity of enantiomers can be determined by optical rotation. Chirality refers to several phenomena, all having to do with objects that differ from their mirror image. ... When polarized light is passed through a substance containing chiral molecules (or nonchiral molecules arranged asymmetrically), the direction of polarization can be changed. ...

More definitions

• Any non-racemic chiral substance is called scalemic.
• A chiral substance is enantiopure or homochiral when only one of two possible enantiomers is present.
• A chiral substance is enantioenriched or heterochiral when an excess of one enantiomer is present but not to the exclusion of the other.
• Enantiomeric excess or ee is a measure for how much of one enantiomer is present compared to the other. For example, in a sample with 40% ee in R, the remaining 60% is racemic with 30% of R and 30% of S, so that the total amount of R is 70%.

In chemistry, a racemate is a mixture of equal amounts of left- and right-handed stereoisomers of a chiral molecule. ...

Enantioselective preparations

Main article: Asymmetric synthesis

Several strategies exist for the preparation of enantiopure compounds. This first method is the separation of a racemic mixture into its isomers, a process called chiral resolution. Louis Pasteur in his pioneering work was able to isolate the isomers of tartaric acid because they crystallize from solution as crystals each with a different symmetry. A less common method is by enantiomer self-disproportionation. The two optical isomers of bromochlorofluoromethane Asymmetric synthesis, also called chiral synthesis, enantioselective synthesis or stereoselective synthesis, is organic synthesis which introduces one or more new and desired elements of chirality. ... Chiral resolution in chemistry is a process for the separation of racemic compounds into their enantiomers [1]. Two common methods are: Derivatization of racemic compounds with optically pure reagents forming pairs of diastereomers which can be separated by conventional techniques in physical chemistry. ... Louis Pasteur (December 27, 1822 – September 28, 1895) was a French chemist best known for his remarkable breakthroughs in microbiology. ... Tartaric acid or H2C4H4O6 is a white crystalline organic acid. ... Enantiomer self-disproportionation is a process in stereochemistry describing the separation of a non-racemic mixture of enantiomers in an enantioenriched fraction and a more racemic fraction as a result of the formation of heterochiral or homochiral aggregates. ...

Other methods are chiral pool synthesis: using chiral starting material and maintaining the chirality; asymmetric induction, the use of chiral auxiliaries, chiral reagents, and chiral catalysts to favor the reaction of one diastereomer over another, and the use of biocatalysts. Chiral pool synthesis is a strategy that aims to improve the efficiency of chiral synthesis. ... Asymmetric induction in stereochemistry describes the preferential formation in a chemical reaction of one enantiomer or diastereoisomer over the other as a result of the influence of a chiral feature present in the substrate, reagent, catalyst or environment [1]. Asymmetric induction is a key element in asymmetric synthesis. ... A chiral auxiliary is a chemical compound or unit that is temporarily incorporated into an organic synthesis so that it can be carried out asymmetrically with the selective formation of one of two enantiomers [1] [2] . Chiral auxiliaries are optically active compounds and introduce chirality in otherwise racemic compounds. ... Biocatalysis can be defined as the utilization of natural catalysts, called enzymes, to perform chemical transformations on organic compounds. ...

Enantioconvergent synthesis is the the synthesis of one enantiomer from a racemic precursor molecule utilizing both enantiomers.

Enantiopure medications

Advances in industrial chemical processes have made it economical for pharmaceutical manufacturers to take drugs that were originally marketed in racemic form and market the individual enantiomers, each of which may have unique properties. For some drugs, such as zopiclone, only one enantiomer (eszopiclone) is active; the FDA has allowed such once-generic drugs to be patented and marketed under another name. In other cases, such as ibuprofen, it is not economically feasible to isolate a single enantiomer from a racemic mixture or to synthesize just the active one, and therefore a racemic mixture is marketed, with an essentially doubled recommended dose. Zopiclone (trade names: Imovane™ and Zimovane™) is a novel hypnotic agent used in the treatment of insomnia. ... Eszopiclone, marketed by Sepracorand marco under the brand-name Lunesta®, is a nonbenzodiazepine hypnotic agent (viz. ... Ibuprofen (INN) (IPA: ) is a non-steroidal anti-inflammatory drug (NSAIDs) originally marketed as Nurofen and since under various trademarks including Act-3, Advil, Brufen, Dorival, Herron Blue, Panafen, Motrin, Nuprin and Ipren or Ibumetin (Sweden), Ibuprom (Poland), IbuHEXAL, Moment (Italy), Ibux (Norway). ...

Examples of racemic mixtures and the corresponding single-enantiomer products that have been marketed include:

• Amphetamine (Benzedrine; street amphetamine is also racemic) and dextroamphetamine (Dexedrine)
• Bupivacaine (Marcain) and levobupivacaine (Chirocaine)
• Cetirizine (Zyrtec) and levocetirizine (Xyzal)
• Citalopram (Celexa / Cipramil) and escitalopram (Lexapro / Cipralex)
• Methylphenidate (Ritalin) and dexmethylphenidate (Focalin)
• Modafinil (Provigil) and armodafinil (Nuvigil)
• Ofloxacin (Floxin) and levofloxacin (Levaquin)
• Omeprazole (Prilosec) and esomeprazole (Nexium)
• Salbutamol (Ventolin) and levalbuterol (Xopenex)
• Zopiclone (Imovane) and eszopiclone (Lunesta)

Thalidomide is an example of a racemic drug, in which one enantiomer produces a desirable antiemetic effect, whereas the other is toxic and produces a teratogenic side-effect. However, the enantiomers are converted into each other in vivo, so chemical processes may not be used to mitigate its toxicity. Amphetamine or Amfetamine (Alpha-Methyl-PHenEThylAMINE), also known as, beta-phenyl-isopropylamine, and benzedrine, is a prescription stimulant commonly used to treat Attention-deficit hyperactivity disorder (ADHD) in adults and children. ... Dextroamphetamine is a powerful psychostimulant which produces increased wakefulness, energy and self-confidence in association with decreased fatigue and appetite. ... Bupivacaine is a local anesthetic. ... Levobupivacaine (rINN) (IPA: ) is a local anaesthetic drug belonging to the amino amide group. ... Cetirizine hydrochloride (IPA sɛ.ˈtɪɹ.ɪ.ˌzin) is a major metabolite of hydroxyzine, and a racemic selective H1 receptor antagonist used in the treatment of allergies, hay fever, angioedema, and urticaria. ... Levocetirizine (as levocetirizine dihydrochloride) is a third generation non-sedative antihistamine, developed from the second generation antihistamine cetirizine. ... Citalopram is an antidepressant drug used to treat depression associated with mood disorders. ... Lexapro pills Escitalopram (Lexapro, Cipralex, Sipralexa and Seroplex)[1] is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) class. ... Vitamin R redirects here. ... Dexmethylphenidate (commercially known as Focalin) is a pharmaceutical drug used to treat Attention Deficit Hyperactivity Disorder. ... Modafinil is a eugeroic drug generally prescribed to treat narcolepsy, made by the pharmaceutical company Cephalon Inc. ... Armodafinil (Nuvigil®) is a drug produced by the pharmaceutical company Cephalon, currently in the process of receiving FDA approval. ... Ofloxacin sold under the brand name Floxin in the US. It is a quinolone antibiotic. ... Levofloxacin is an advanced generation fluoroquinolone antibiotic, marketed by Ortho-McNeil under the trade name Levaquin in the United States. ... Omeprazole (INN) (IPA: ) is a proton pump inhibitor (brand names Antra® in Italy) used in the treatment of dyspepsia, peptic ulcer disease (PUD), gastroesophageal reflux disease (GORD/GERD) and Zollinger-Ellison syndrome. ... Esomeprazole is a proton pump inhibitor used in the treatment of dyspepsia, peptic ulcer disease (PUD), GERD and Zollinger-Ellison syndrome. ... Salbutamol (INN) or albuterol (USAN) is a short-acting β2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and COPD. Salbutamol sulphate is usually given by the inhaled route for direct effect on bronchial smooth muscle. ... Levalbuterol (Xopenex®) is the R-enantiomer of the short-acting β2-adrenergic receptor agonist albuterol. ... Zopiclone (trade names: Imovane™ and Zimovane™) is a novel hypnotic agent used in the treatment of insomnia. ... Eszopiclone, marketed by Sepracorand marco under the brand-name Lunesta®, is a nonbenzodiazepine hypnotic agent (viz. ... // Thalidomide is a sedative, hypnotic, and anti-inflammatory medication. ... An antiemetic is a drug that is effective against vomiting and nausea. ... Teratogenesis is a medical term from the Greek, literally meaning monster making. ...

External links

• Infelicitous stereochemical nomenclatures for stereochemical nomenclature
• US FDA's policy statement on the development of new stereoisomeric drugs