Chirality

Chirality is a geometric property of an object that is not superimposable on its mirror image. The term, derived from the Greek cheir for hand, is used in chemistry and biology to describe molecules and structures that exist as two non-superimposable mirror-image forms, called enantiomers. A chiral object typically contains a stereogenic element, such as a carbon atom bonded to four different substituents (a chiral center), though chirality can arise from axial, planar, or other arrangements without a single stereocenter.

Enantiomers share the same chemical formula and many physical properties, but they interact differently with other chiral systems, including biological molecules. This often leads to distinct behaviors in biological contexts, such as metabolism, signaling, and pharmacological activity. Chiral molecules can rotate plane-polarized light, a property known as optical activity; the measurement is reported as a specific rotation. A mixture with equal amounts of both enantiomers is called racemic and is typically optically inactive.

Chirality has practical significance in synthesis and manufacturing. Enantioselective synthesis and resolution techniques aim to produce or separate a preferred enantiomer, which is especially important in pharmaceuticals, where different enantiomers can have different efficacy or safety profiles. In biology, most living systems display homochirality, with proteins built from left-handed amino acids and nucleic acids from right-handed sugars.

Analytical methods such as circular dichroism spectroscopy and X-ray crystallography are used to study chirality in molecules and materials. Beyond chemistry, chirality also appears in certain materials and in considerations of fundamental physics, where symmetry and parity play related roles in describing interactions.