Tautomerism : Structural Isomers that undergo rapid interconversions and exist in dynamic equilibrium are known as Tautomers and relationship between them is known as Tautomerism. Tautomers generally have different functional groups. At equilibrium more stable tautomer is present in higher amount by ratio remains same until and unless change is made externally. Tautomerism actually arises due to rapid oscillation of an atoms between two polyvalent atoms in a molecule underset("Keto form")(underset(H)underset(|)(C)H_(2)-overset(O)overset(||)(CH)) hArr underset("enol form")(CH_(2)=overset(OH)overset(|)(CH) Above is an example of Keto-enole tautomerism. condition for this type of keto enol tautomerism is presence of alpha-H. amount of enol at equilibrium is known as enolic content. it is more if enol is more stable and less if keto is more stable. Tautomers of which of the following can show geometrical isomerism