A property possessed by certain crystals and solutions of rotating the plane of polarization of polarized light. The activity is called dextrorotatory if the rotation is clockwise when facing the light, and laevorotatory when it is anticlockwise. It occurs when a molecule exists in two mirror-image forms that cannot be superimposed on one another.
Various methods exist for denoting the molecular configuration of optical isomers.
Note that the d-form of a compound need not necessarily be dextrorotatory. A mixture containing both isomers in equal proportions is called a racemic mixture . Optical activity occurs in molecules possessing chirality . Oxford Paperback Encyclopedia 4. Oxford University Press 5.