Editing Enantiomer (section)

==Naming conventions==
{{Main|Absolute configuration}}

There are three common naming conventions for specifying one of the two enantiomers (the [[absolute configuration]]) of a given chiral molecule: the R/S system is based on the geometry of the molecule; the (+)- and (−)- system (also written using the obsolete equivalents ''d''- and ''l''-) is based on its [[optical rotation]] properties; and the <small>D</small>/<small>L</small> system is based on the molecule's relationship to enantiomers of [[glyceraldehyde]].

The R/S system is based on the molecule's geometry with respect to a chiral center.<ref name=":0">{{Cite journal |last=Brewster |first=James H. |date=December 1986 |title=The distinction of diastereomers in the Cahn-Ingold-Prelog (RS) notation |url=https://pubs.acs.org/doi/abs/10.1021/jo00375a001 |journal=The Journal of Organic Chemistry |language=en |volume=51 |issue=25 |pages=4751–4753 |doi=10.1021/jo00375a001 |issn=0022-3263}}</ref> The R/S system is assigned to a molecule based on the priority rules assigned by [[Cahn–Ingold–Prelog priority rules]], in which the group or atom with the largest atomic number is assigned the highest priority and the group or atom with the smallest atomic number is assigned the lowest priority.

The (+) or (−) symbol is used to specify a molecule's [[optical rotation]] — the direction in which the polarization of light rotates as it passes through a solution containing the molecule.<ref>{{Cite journal |last1=Caldwell |first1=John |last2=Wainer |first2=Irving W. |date=December 2001 |title=Stereochemistry: definitions and a note on nomenclature |url=https://onlinelibrary.wiley.com/doi/10.1002/hup.334 |journal=Human Psychopharmacology: Clinical and Experimental |language=en |volume=16 |issue=S2 |pages=S105–S107 |doi=10.1002/hup.334 |pmid=12404716 |s2cid=12367578 |issn=0885-6222}}</ref> When a molecule is denoted dextrorotatory, it rotates the plane of polarized light clockwise and can also be denoted as (+).<ref name=":0" /> When it is denoted as levorotatory, it rotates the plane of polarized light counterclockwise and can also be denoted as (−).<ref name=":0" /> 

The Latin words for ''left'' are ''laevus'' and ''sinister'', and the word for ''right'' is ''dexter'' (or ''rectus'' in the sense of correct or virtuous). The English word ''right'' is a [[cognate]] of ''rectus''. This is the origin of the D/L and R/S notations, and the employment of prefixes [[Dextrorotation and levorotation|''levo-'' and ''dextro-'']] in [[Systematic name|common names]].

The prefix ''ar-'', from the Latin ''recto'' (right), is applied to the right-handed version; ''es-'', from the Latin ''sinister'' (left), to the left-handed molecule. Example: [[ketamine]], [[arketamine]], [[esketamine]].<ref>{{Cite journal|url=https://doi.org/10.1001/jamanetworkopen.2021.5731|title=Evaluation of Trials Comparing Single-Enantiomer Drugs to Their Racemic Precursors: A Systematic Review|first1=Aaron S.|last1=Long|first2=Audrey D.|last2=Zhang|first3=Caitlin E.|last3=Meyer|first4=Alexander C.|last4=Egilman|first5=Joseph S.|last5=Ross|first6=Joshua D.|last6=Wallach|date=May 6, 2021|journal=JAMA Network Open|volume=4|issue=5|pages=e215731|via=Silverchair|doi=10.1001/jamanetworkopen.2021.5731|pmid=33956134 |pmc=8103227}}</ref>