Question

Question: Which of the following pairs of compounds represent keto–enol tautomers?

a.

b.

c.

d.

Short answer

Answer

a. Keto-enol tautomers

b. Not keto-enol tautomers

c. Keto-enol tautomers

d. Not keto-enol tautomers

Step-by-step solution

Step-by-Step SolutionStep 1: Keto-enol tautomer

Keto-enol tautomerism is the result of a change in the site of the double bond and hydrogen in the constitutional isomer. In enol, the OH must be bonded to a $\mathrm{C}=\mathrm{C}$.

Example of keto-enol tautomerism

An example of keto-enol tautomerism is shown below:

Representation of keto-enol tautomerism

Finding whether it is keto-enol tautomer

Representation of keto-enol tautomerism of a

Compare both the figures. The first figure contains a C=O and an additional CH bond, and the second figure has a C=C, and the OH is attached to the C=C. So by the definition, it is a keto-enol tautomer.

Representation of keto-enol tautomerism of b

Compare both the figures. The first figure contains a C=O and an additional CH bond, but in the second figure, the OH is not attached to the C=C. So by the definition, it is not a keto-enol tautomer.

Representation of keto-enoltautomerism of c

Comparing both the figures, the first figure has a C=C. The OH is attached to the C=C and the second figure contains a C=O and an additional CH bond. So by the definition, it is a keto-enol tautomer.

Representation of keto-enoltautomerism of d

Compare both the figures. The first figure contains a C=O and an additional CH bond, but in the second figure, the OH is not attached to the C=C. So by the definition, it is not a keto-enol tautomer.