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Question
Among the given compounds, the correct order of enol content is:
Among the given compounds, the correct order of enol content is:
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Solution
The correct option is C II > I > III
In Keto-enol tautomerism, delocalisation takes place between a >C=O group and an alpha H where the equilibrium lies between a keto form and an enol form.
Enol form of (II) has 6-π electrons which obeys the 4n+2 rule of Huckel's. Hence, the enol form will be aromatic and thus it is more stable than its Keto form.
Comparing compounds I and III :
Since, I is a ketone and III is an ester. Alpha-hydrogen in ketone is more acidic as compared to ester. Moreover, generally esters do not show tautomerism as on removing the alpha H there is cross conjugation (with lone pair of O) which destablises the enol form. Therefore, I is more prone to show keto-enol tautomerism, and enol content will be more for I as compared to III
Hence, the order of enol content is
II > I > II
In Keto-enol tautomerism, delocalisation takes place between a >C=O group and an alpha H where the equilibrium lies between a keto form and an enol form.
Enol form of (II) has 6-π electrons which obeys the 4n+2 rule of Huckel's. Hence, the enol form will be aromatic and thus it is more stable than its Keto form.
Comparing compounds I and III :
Since, I is a ketone and III is an ester. Alpha-hydrogen in ketone is more acidic as compared to ester. Moreover, generally esters do not show tautomerism as on removing the alpha H there is cross conjugation (with lone pair of O) which destablises the enol form. Therefore, I is more prone to show keto-enol tautomerism, and enol content will be more for I as compared to III
Hence, the order of enol content is II > I > II
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