A chiral molecule /ˈkaɪərəl/ is a type of molecule that has a non-superposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom.[1][2]

The term chiral in general is used to describe an object that is not superposable on its mirror image.[3][4] Achiral (not chiral) objects are objects that are identical to their mirror image. Human hands are perhaps the most universally recognized example of chirality: the left hand is a non-superposable mirror image of the right hand; no matter how the two hands are oriented, it is impossible for all the major features of both hands to coincide. This difference in symmetry becomes obvious if a left-handed glove is placed on a right hand. The term chirality is derived from the Greek word for hand, χειρ (kheir). It is a mathematical approach to the concept of "handedness".

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The symmetry of a molecule (or any other object) determines whether it is chiral. A molecule is achiral (not chiral) when an improper rotation, that is a combination of a rotation and a reflection in a plane, perpendicular to the axis of rotation, results in the same molecule - see chirality (mathematics). For tetrahedral molecules, the molecule is chiral if all four substituents are different.

A chiral molecule is not necessarily asymmetric (devoid of any symmetry element), as it can have, for example, rotational symmetry.