Question

Choose the correct statement(s) for the following compounds :

• A. Compound (a) does not show tautomerism.
• B. Compound (b) shows tautomerism
• C. Compound (d) has a stable enol form
• D. Compound (c) does not show tautomerism

Answer 1

Answer: (A), (C), (D)

Compound (c) does not show tautomerism

Tautomerism is a phenomenon where a single compound tends to exist in two or more structures which are interconvertible and differ in the relative position of one atomic nucleus.

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.

Here, compounds (a) , (b) and (c) do not have a enol form due to absence of H-atom on the carbon adjacent to carbonyl group.
For (d) , enol form :


It is planar , all C atoms are $s{p}^2$ hybridised.
Has conjugation
Follows Huckel's rule $(4n+2)e^{-}$ , since it has $2\pi e^{-}$
Hence, highly stable due to aromaticity.