Mechanism of Keto-Enol Interconversion

Any reaction that simply involves the intramolecular transfer of a proton is called a tautomerism. Keto-enol interconversion may happen in basic as well as acidic solution. The steps are reversed in the base-catalyzed and acid-catalyzed reactions. In the base-catalyzed reaction, the first step is removal of an a-proton and the 

The enol form is so-called because it is a combination of ene for the double bond and ol for the -OH (hydroxyl) group. The two isomers exist in equilibrium, and in any such case both tautomers are present, but in simple cases the keto form is much more stable than the enol form. For example, in acetaldehyde about six molecules out of every 10 million molecules are in the enol form at any given time. Nevertheless, the equilibrium always exists, and every molecule of acetaldehyde (as well as any other aldehyde or ketone with an alpha hydrogen) is converted into the enol form (and back again) several times per second. This is an important 

On dilution, the intermolecular hydrogen bonds (between two different types of molecules like A and ZH are broken and, therefore, the percentage of enol form in the mixture increases. Two factors usually stabiHze the enol form  

1) Intramolecular hydrogen bonding hydrogen bond formation within the same molecule as shown below in the enol form of l,3Kliketones  

In the series of ds-fixed bicyclic diketones 13-15 the percentage enol varies from 100 to 80 to 1.4, respectively in this series the hydrogen bond becomes obviously longer and weaker. For disubstituted 1,3-diketones (16) the enol content increases rapidly as the size of the alkyl substituent is increased, when R is fert-butyl the 

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