Chiral molecules are isomers. Isomers are compounds with the same formula, but contain a different arrangements of atoms and different chemical and physical properties. Structural isomers are compounds that contain the same atoms but the bonds within the compound differ. Stereoisomers have different spatial arrangements of the atoms even though they contain the same bonds. One type of stereoisomerism is optical isomerism.
Optical isomers have opposite effects on plane-polarized light.
Molecules that have nonsuperimposable images have been found to exhibit this optical activity. These nonsuperimposable isomers are called enantiomers, which rotate plane-polarized light as it is passed through the compound in opposite directions. If the plane of light is rotated to the right, the optically active compound is a compound in the dextrorotary form. If the isomer rotates the plane of vibration to the left, the compound is said to levorotary. Although their chemical and physical properties are very similar, a pair of optical isomers can have biological behaviors that are profoundly different.