Some chemicals, principally complex organic
molecules, can exist in two mirror-image forms. They have exactly the same chemical composition and cannot be distinguished by most simple chemical or physical tests. However, these enantiomers
are subtly different, the same way that my right hand and left hand are different (This property is called "chirality
," but informal
ly called "handedness
"). Some molecules can even have mirror-imaged bonds at several positions, such that the total number of enantiomers is 2^n, where n is the number of bonds in question. For example, a molecule like vitamin E
that has three such points could exist as RRS (r indicates one direction, s another), RRR, RSR, RSS, SRR, SRS, SSR, or SSS (2^3 = 8).
Inorganic synthetic processes usually produce equal quantities of each enantiomer. Such a mixture is called a racemate
, because chirality was first noted in the crystals of racemic acid.
Chiral molecules in crystalline form have the property of rotating polarized light either left or right. Racemates can be detected because they do not cause light to rotate; the different enantiomers cancel each other out.