Optical Isomerism (Chirality)

Molecules that are not superimposable on their mirror images are termed dissymmetric (chiral). All asymmetric molecules (C1 symmetry) are dissymmetric, but the converse is not true. The relation between molecular symmetry and dissymmetric character is expressed by the following rule:

A molecule that has no improper rotation axis must be dissymmetric.

Improper rotation axises in 3 dimensions are rotation reflection axises Sn, mirror planes (S1) and inversion center (S2). The determinant of the transformation matrix for a proper rotation axis is always +1; the determinant of the transformation matrix for an improper rotation axis is always -1.
Last update March, 5th 2013 by A. Gelessus