Question

The number of compound(s) in which keto form is more dominating than enol form is/are:

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

The correct option is C 3

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.

In below compound, the keto form is more stable than enol form because the enol form has 4-$\pi$ electrons which obeys 4n rule and thus it is an antiaromatic so it is less stable. So Keto form dominates over enol.

In below compound, the keto form is more stable because in enol form double bond can occurs at bridgehead carbon so by Bredt's rule it is less stable. Hence keto form dominates enol form.

In below compound, the Keto form is more stable because in enol form due to steric hindrance of bulky tertiary alkyl group the H-bonding is less favoured, hence enol form becomes less stable.

In below compound, enol form dominates over keto form because the enol form is stabilised by conjugated double bond and by the formation of 6 membered cyclic ring by hydrogen bonding. Thus, enol group dominates over keto form.

Therefore, in 3 compounds keto form is dominating than enol form