Racemization

Racemization

In chemistry racemization refers to partial conversion of one enantiomer into another.

Stereochemistry

Chiral molecules have two forms (at each point of asymmetry) which differ in their optical characteristics: the "levorotatory form" (the "(−)-form") will rotate the plane of polarization of a beam of light to the left, while the "dextrorotatory" form (the "(+)-form") will rotate the plane of polarization of a beam of light to the right. The two forms, which are non-superimposable when rotated in 3 dimensional space, are said to be "diastereomers".

A common misconception is that in order for a point of asymmetry to exist there must be four different groups attached to the central atom (the chiral center). Whilst this is true in all cases of molecules with chiral atoms, it is possible for chirality to occur without the need of an actual chiral centre. When considering chemical stereochemistry it's important to recall that molecules exist in 3 dimensional space, and as such can have different arrangement of the atoms in that space.

Physical properties

Diastereomers have similar chemical properties yet have differing physical properties. Via processes such as crystallization one diastereomer can be isolated.

Biological importance

Generally only one form of a chiral molecule will participate in biochemical reactions while the other simply does not participate or can cause sideffects in the form of side reactions. Of note, the L form is usually the biologically reactive form.

Formation of racemic mixtures

Substitution reactions that proceed through a carbocation intermediate (such as unimolecular substitution reactions) lead to the non-stereospecific addition of substituents. While unimolecular elimination reactions also proceed through a carbocation, they do not result in a chiral center, rather they result in a set of geometric isomers in which "trans/cis" or "E/Z" forms will result

The rate of racemization (from L-forms to a mixture of L-forms and D-forms) has been used as a way of dating biological samples in tissues with slow rates of turnover, forensic samples and fossils in geological deposits.

See also

*Racemic


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Look at other dictionaries:

  • racemization — [ras΄ə mi zā′shən] n. the conversion of an optically active substance into a racemic form …   English World dictionary

  • racemization — racemizacija statusas T sritis chemija apibrėžtis Racemato susidarymas vienam enantiomerui virstant kitu. atitikmenys: angl. racemization rus. рацемизация …   Chemijos terminų aiškinamasis žodynas

  • racemization — noun Date: 1895 the action or process of changing from an optically active compound into a racemic compound or mixture • racemize verb …   New Collegiate Dictionary

  • racemization — /ras euh meuh zay sheuhn, ray see meuh /, n. Chem. the conversion of an optically active substance into an optically inactive mixture of equal amounts of the dextrorotatory and levorotatory forms. [1890 95; RACEME + IZATION] * * * …   Universalium

  • racemization — noun The formation of a racemate from a pure enantiomer. See Also: racemize …   Wiktionary

  • racemization — Partial conversion of one enantiomorph into another (as an l amino acid to the corresponding d amino acid) so that the specific optical rotation is decreased, or even reduced to zero, in the resulting mixture. * * * ra·ce·mi·za·tion also Brit… …   Medical dictionary

  • racemization — race·mi·za·tion …   English syllables

  • racemization — rac•e•mi•za•tion [[t]ˌræs ə məˈzeɪ ʃən, reɪˈsi mə , rə [/t]] n. chem. the conversion of an optically active substance into an optically inactive mixture of equal amounts of the dextrorotatory and levorotatory forms • Etymology: 1895 …   From formal English to slang

  • racemization — ˌrasəmə̇ˈzāshən; rāˌsēm , rəˌs noun ( s) Etymology: racemize + ation : the action or process of changing from an optically active compound into a racemic compound or mixture opposed to resolution …   Useful english dictionary

  • Amino acid dating — is a technique used to estimate age in a wide variety ofsituations. This technique relates changes in amino acid molecules to thetime elapsed since they were formed. This technique is used in paleobiology, archaeology, forensic science, and… …   Wikipedia

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