Chemistry - STRUCTURAL ISOMERISM Question with Solution | TestHub

Question Explanation:

The question asks which compound has the highest percentage of enol form in keto-enol equilibrium.

Concept:

Enol content increases with:

Resonance stabilization

Intramolecular hydrogen bonding

Presence of an active methylene group

Conjugation in the enol form

Solution:

1. Acetylacetone (CH₃CO–CH₂ –COCH₃ )

A β-diketone whose enol form is highly stabilized by resonance and six-membered intramolecular

H-bonding

→ maximum enol content (approx 76% enol)

1 .

2. Ethyl acetoacetate (CH₃CO–CH₂–COOC₂H₅)

A β-keto ester; the ester group reduces enol stabilization → lower enol content.

3. Ethyl acetate (CH₃COOC₂H₅)

A simple ester with negligible enol content.

4. Diethyl malonate (C₂H₅OOC–CH₂–COOC₂H₅)

A β-diester; the strong -M effect of the ester groups further reduces enol stability.

Final Answer: Option (A)