Question

Which of the following compounds have their keto-form to be more stable?

• A.
• B.
• C.
• D. All of these

Answer 1

The correct option is D All of these

a) Enol form violates Bredt's rule. Since the bridge head carbon of enol becomes $s{p}^2$ and creates angle strain so keto-enol equilibrium shifted toward more stable keto form.

b) Keto form is more stable because it is non planar when it goes to enol form, the induced planarity encounters steric repulsion from bulkier tert-butyl group.

c) Enol form results into formation of antiaromati cyclobutadiene which is unstable so this compound predominates in keto form.