quiral

Quiral is a term used in several languages to refer to chirality, the geometric property of an object being non-superimposable on its mirror image. In English, the preferred term is chirality; “quiral” is used as a direct loanword in some languages. The concept is central to stereochemistry and many fields of science.

A chiral object lacks an internal plane of symmetry and is not superimposable on its mirror image. The pair of mirror images are enantiomers. In chemistry, a molecule is often chiral if it contains at least one stereogenic center, commonly a tetrahedral carbon connected to four different substituents, but chirality can also arise from axial, planar, or helical arrangements.

Enantiomers have identical physical properties in achiral environments but rotate plane-polarized light in opposite directions and interact differently with other chiral substances, such as enzymes. A mixture containing equal amounts of both enantiomers is a racemate; mixtures with unequal amounts are described by enantiomeric excess.

Methods to determine or separate chirality include polarimetry, chiral chromatography, NMR with chiral shift reagents, and circular dichroism. In applications, chirality is especially important in pharmacology, since enantiomers of a drug can have different activity, potency, or safety profiles. Therefore, asymmetric synthesis, chiral resolution, and the use of chiral auxiliaries are common strategies to obtain enantiomerically pure compounds.

See also: achirality, enantiomer, diastereomer, stereochemistry, chirality center.