Editing Enantiomer (section)

== Chirality centers ==
[[File:Meso-Weins%C3%A4ure_Spiegel.svg|thumb|150px|[[Fischer projection]] of meso-tartaric acid]]
The asymmetric atom is called a '''chirality center''',<ref>{{GoldBookRef|title=''chirality centre''|file=C01060}}</ref><ref name="Wade 2006">{{cite journal | last=Wade | first=LeRoy G. | title=Precision in Stereochemical Terminology | journal=J. Chem. Educ. | volume=83 | issue=12 | year=2006 | issn=0021-9584 | doi=10.1021/ed083p1793 | page=1793| bibcode=2006JChEd..83.1793W }}</ref> a type of [[stereocenter]]. A chirality center is also called a ''chiral center''<ref name="Karras 2018">{{cite thesis |last=Karras |first=Manfred |date=2018 |title="Synthesis of Enantiomerically Pure Helical Aromatics Such As NHC Ligands and Their Use in Asymmetric Catalysis |type=PhD |publisher=Charles University |url=https://dspace.cuni.cz/handle/20.500.11956/104319 |access-date=6 August 2021}}</ref><ref name="Eliel 1994">{{Cite book|title=Stereochemistry of organic compounds|last1=Eliel |first1=Ernest L.|date=1994|publisher=Wiley|last2=Wilen |first2=Samuel H. |last3=Mander |first3=Lewis N.|isbn=0471016705|location=New York|oclc=27642721}}</ref><ref name="Clayden 2012">{{cite book | last1=Clayden | first1=Jonathan | last2=Greeves | first2=Nick | last3=Warren | first3=Stuart G. | title=Organic chemistry | publisher=Oxford University Press | publication-place=Oxford | date=2012 | isbn=978-0-19-927029-3 | oclc=761379371 | page=}}</ref> or an ''asymmetric center''.<ref>{{GoldBookRef|title=''asymmetric centre''|file=A00480}}</ref> Some sources use the terms ''stereocenter'', ''stereogenic center'', ''stereogenic atom'' or ''stereogen'' to refer exclusively to a chirality center,<ref name="Karras 2018" /><ref name="Clayden 2012" /><ref name="Clark 2021">{{cite book | last1=Clark | first1=Andrew | last2=Kitson | first2=Russell R. A. | last3=Mistry | first3=Nimesh | last4=Taylor | first4=Paul | last5=Taylor | first5=Matthew | last6=Lloyd | first6=Michael | last7=Akamune | first7=Caroline | title=Introduction to stereochemistry | publication-place=Cambridge, UK | date=2021 | isbn=978-1-78801-315-4 | oclc=1180250839}}</ref> while others use the terms more broadly to refer also to centers that result in [[diastereomers]] (stereoisomers that are not enantiomers).<ref name="Wade 2006" /><ref>{{GoldBookRef|title=''stereogenic unit (stereogen/stereoelement)''|file=S05980}}</ref><ref name="Mislow 1984">{{cite journal | last1=Mislow | first1=Kurt | last2=Siegel | first2=Jay | title=Stereoisomerism and local chirality | journal=J. Am. Chem. Soc. | volume=106 | issue=11 | year=1984 | issn=0002-7863 | doi=10.1021/ja00323a043 | pages=3319–3328| bibcode=1984JAChS.106.3319M }}</ref>

Compounds that contain exactly one (or any odd number) of asymmetric atoms are always chiral. However, compounds that contain an even number of asymmetric atoms sometimes lack chirality because they are arranged in mirror-symmetric pairs, and are known as [[Meso compound|''meso'' compounds]]. For instance, ''meso'' [[tartaric acid]] (shown on the right) has two asymmetric carbon atoms, but it does not exhibit enantiomerism because there is a  mirror symmetry plane. Conversely, there exist forms of chirality that do not require asymmetric atoms, such as [[Axial chirality|axial]], [[Planar chirality|planar]], and [[Helical chirality|helical]] chirality.<ref name="Karras 2018" />{{Rp|pg. 3}}

Even though a chiral molecule lacks reflection (C<sub>s</sub>) and [[improper rotation|rotoreflection]] symmetries (S<sub>2''n''</sub>), it can have other [[Molecular symmetry|molecular symmetries]], and its symmetry is described by one of the chiral [[Point groups in three dimensions|point groups]]: C<sub>''n''</sub>, D<sub>''n''</sub>,  T, O, or I. For example, [[hydrogen peroxide]] is chiral and has C<sub>2</sub> (two-fold rotational) symmetry. A common chiral case is the point group C<sub>1</sub>, meaning no symmetries, which is the case for lactic acid.
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