What does achiral mean?
Achiral describes an object or molecule that is identical to its own mirror image — one that can be perfectly superimposed on its reflection, with no 'handedness'. The word belongs chiefly to chemistry, where it marks a fundamental distinction: a chiral molecule, like a left hand, cannot be matched onto its mirror image, while an achiral molecule, like a plain sphere or a symmetrical mug, can. Achirality usually arises from some internal symmetry — a plane, centre, or axis of symmetry within the structure. The distinction matters practically because chiral and achiral substances behave differently toward polarized light and toward other chiral entities, including many biological molecules; a drug's activity, for instance, can depend entirely on its handedness. Chemists routinely describe solvents, reagents, intermediates, and environments as achiral when they show no preference between mirror-image forms. Though unfamiliar outside the laboratory, the concept offers a vivid lesson in symmetry: most everyday objects around us are, in this precise sense, achiral.
adjectiveOf a molecule or object: identical to its mirror image, so that the two can be superimposed on each other; lacking handedness or chirality.
- (Chemistry) Of a molecule: having a structure that is superimposable on its mirror image, typically because it possesses a plane, centre, or axis of symmetry; such molecules do not exhibit optical activity.
- (General geometry/physics) Of any three-dimensional object: indistinguishable from its mirror image; lacking handedness.
"Because the molecule has an internal plane of symmetry, it is achiral and does not rotate plane-polarized light."
"Water and methane are achiral molecules, so their solutions never rotate plane-polarized light."
"In a synthesis designed for drug manufacture, chemists must know whether an intermediate is achiral, since only chiral products can exist as distinct enantiomers."
Your hands are chiral — but a plain coffee mug is achiral, because its mirror image is just another mug you could pick up and use.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of achiral
The word combines the Greek-derived prefix 'a-' (meaning 'without') with 'chiral', a term introduced by Lord Kelvin in the late nineteenth century from the Greek 'cheir', meaning 'hand' — chosen because hands are the classic example of objects that differ from their mirror images. 'Cheir' also underlies words such as 'chiropractic', 'chiromancy', and, through Greek 'cheirourgia', 'surgery'. 'Achiral' thus literally means 'without handedness', and it emerged as chemists formalized the study of molecular symmetry and optical activity.
Related word forms
How achiral is actually used
A technical term used almost exclusively in chemistry, crystallography, and related sciences; rare in everyday speech. It carries no emotional connotation — register is formal and scientific.
Easily confused with achiral
A chiral object differs from its mirror image (like a left and right hand), whereas an achiral object is identical to its mirror image.