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Ethyl Acetoacetate has enol content of 0.4% in water and 19.8% in toluene. What is the reason behind this? Does this anything have to do with the intramolecular hydrogen bonding in the enol form?

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The extent of enolization is affected by the solvent, concentration and temperature. Ethyl acetoacetate has enol content of 0.4% in water and 19.8% in toluene. This is because water reduces the enol content by hydrogen bonding with the carbonyl group making this group less available for intramolecular hydrogen bonding. The effectiveness of intramolecular hydrogen bonding in stabilizing the enol, with respect to the keto form is thus seen on varying the solvent and particularly on transfer to a hydroxylic solvent.

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In water, due to more number of electropositive H present, the O will tend to H-bond with water molecules due to which enolisation hardly occurs although active methylene carbon. But in toluene, since it is a non-polar solvent, intramolecular H-bonding is more favorable due to which % enolisation increases in toluene. But since ester group has some resonance in ethylacetoacetate, the % of enolisation does not increase too much in toluene.

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In non -polar aprotic solvents intra H.B is present in enol form hence, it is more stable but in polar protic solvents H.B is formed with polar solvent molecules hence, intra H.B is absent in the enol form

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