Isomers are types of molecules that share a chemical formula but have difference geometries, resulting in different properties:
* A pure substance is composed of only one type of isomer of a molecule (all have the same geometrical structure).
* Structural isomers have the same chemical formula but different physical arrangements, often forming alternate molecular geometries with very different properties. The atoms are not bonded (connected) together in the same orders.
** Functional isomers are special kinds of structural isomers, where certain groups of atoms exhibit a special kind of behavior, such as an ether or an alcohol.
* Stereoisomers may have many similar physicochemical properties (melting point, boiling point) and at the same time very different biochemical activities. This is because they exhibit a handedness that is commonly found in living systems. One manifestation of this chirality or handedness is that they have the ability to rotate polarized light in different directions.
* Protein folding concerns the complex geometries and different isomers that proteins can take.