text: 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 / 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. 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 (+)- and (−)- is used to specify a molecule's optical rotation — the direction that the molecule rotates in polarized light. When a molecule is denoted dextrorotatory it is rotating the plane of polarized light clockwise and can also be denoted as (+). When it is denoted as levorotatory it is rotating the plane of polarized light counterclockwise and can also be denoted as (−). 
  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 levo- and dextro- in 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.