Chemistry - STRUCTURAL ISOMERISM Question with Solution | TestHub

Compound (b) has the higher enol content. The enol of (a), cyclopent-4-en-1,3-dione, would be a fully conjugated cyclopentadienone-like system with 4 pi electrons in the ring - anti-aromatic and very unstable - so (a) remains essentially completely in the keto form. The enol of (b), cyclohexane-1,3-dione, is 3-hydroxycyclohex-2-en-1-one : conjugated with the second carbonyl and locked by a strong intramolecular hydrogen bond, an ordinarily stabilised enol with no anti-aromatic penalty. Hence enol content of (b) is higher than that of (a).