4. Optically active molecules

4.1 Chirality

More than a century and a half ago, Louis Pasteur had the intuition that an optically active compound, in his case a tartrate, could exist in two isomeric forms, non-superimposable images of each other in a mirror. This property, for a molecule, or more generally for an object, of not being able to superimpose itself on its image in a plane mirror, is called chirality. This term comes from the Greek "keir", the hand: the right hand and the left hand are not equivalent and are each other's image in a mirror. Many other objects are chiral, such as snail shells, springs and ears.