Achiral

Synonyms

Mirror symmetric

Definition

The term “achiral” is applied to any object – in astrobiology most commonly a molecule, a two-dimensional crystal surface, or a three-dimensional crystal structure – that is invariant (i.e., superimposable) with its mirror image. Achiral objects possess a plane of symmetry, either a mirror or a glide plane symmetry operator. Common achiral objects include a soccer ball, a pencil, and the letter “X,” in contrast with chiral objects such as a snail shell, your left hand, and the letter “R.” Common achiral molecules are H₂O, CH₄, and NH₃ in contrast with such chiral biomolecular species as alanine and ribose. In chemistry, achiral should not be confused with racemic, although in neither case is the optical rotation of polarized light affected.

See Also

• Chirality

• Enantiomeric Excess

• Homochirality

• Racemic (Mixture)

• Stereoisomers