Chemistry > Isomerism > 3.0 Tautomerism

  Isomerism
    1.0 Isomerism
    2.0 Structural Isomerism
    3.0 Tautomerism
    4.0 Geometrical isomerism in the compounds containing C=N
    5.0 Optical Isomerism
    6.0 Optical isomerism in compounds having more than one chiral carbons
    7.0 Optically active compounds having no asymmetric carbon

3.6 Mechanism of tautomerism
Acid catalysed tautomerism is a two step process.
(i) Proton transfer from the acid catalyst, H—A, to the carbonyl oxygen forms the conjugate acid of the aldehyde (or) ketone.


(ii) Proton transfer from the $\alpha - $carbon to the base, ${A^\Theta }$ gives the enol and generates a new molecule of the acid catalyst, H—A.


with unsymmetrical ketones, enolization may occur in either of two directions.


the ketone is by far the most abundant species present at equilibrium. Both enols are also present, but in very small concentrations. The enol with the more highly substituted double bond is themore stable of the two enols and is present in higher concentration than the other.

$ * $Percent enol content $\alpha $ conjugation

$\alpha $/Temperature

$\alpha $/Hydrogen bonding

$\alpha $/Base strength
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