See Also: tautomerism(medicine)
tautomerism(encyclopedia)

tautomerism (sh)




Existence of two or more chemical compounds that have the same chemical composition but different structures (isomers) and that convert easily from one to another.

A major class of tautomeric reactions involves exchange of a hydrogen atom between two other atoms in the same molecule, in both cases forming a covalent bond. For example, in keto-enol tautomerism, the hydrogen atom bonded to the carbon atom in a carbonyl (keto) group (¨DCH¨DC=O; see functional group) moves to the oxygen atom, making it an enol group (¨DC=C¨DOH). The keto form predominates in many aldehydes and ketones, the enol form in phenols. Sugars (e.g., glucose) exhibit tautomerism between open (chain) forms and closed (ring) forms. See also isomerism.