Kiraliteter

Kiraliteter refers to the geometric property of an object that is not superimposable on its mirror image. In chemistry, chirality describes molecules or ions that exist in two non-superimposable mirror-image forms, known as enantiomers. The term derives from the Greek cheir, meaning hand.

A molecule is chiral if it contains a stereogenic element, most commonly a stereogenic center such as a carbon atom bonded to four different substituents. Molecules with such centers can occur as two enantiomers with opposite configurations (R and S according to the Cahn–Ingold–Prelog rules). Some chiral entities arise through restricted rotation or helical structures, while many molecules without such centers can still be chiral.

Enantiomers have identical physical properties in achiral environments, but they differ in how they interact with polarized light, rotating the plane of polarization in opposite directions. Optical activity is quantified by the specific rotation [α], and the mixture of equal amounts of enantiomers is called a racemate and is optically inactive. A mixture with unequal amounts shows enantiomeric excess. Achiral molecules possess symmetry elements such as a mirror plane or center of inversion and are not optically active.

Chirality has major implications in chemistry, especially in pharmacology, where enantiomers can have different biological activities or toxicities. Consequently, enantioselective synthesis and separation of enantiomers are important fields, with applications in drug development and asymmetric catalysis. In nature, biomolecules are often homochiral, using one dominant handedness, such as L-amino acids and D-sugars.