Question

The order of stability of the following tautomeric compounds is

• A. I > II > III
• B. III > II > I
• C. II > I > III
• D. II > III > I

Answer 1

The Correct Option is B

The question involves comparing the stability of three tautomeric compounds. Tautomerism is a phenomenon where compounds exist in two (or more) readily interconvertible structures that differ notably in the placement of a proton and the double bond (commonly keto-enol tautomers).

The stability of tautomeric forms can be influenced by several factors including:

• Hydrogen bonding
• Resonance stability
• Hyperconjugation
• Steric effects

We will analyze the given compounds:

1. Structure I: An enol form with an -OH group attached to a carbon-carbon double bond. Less stable due to the lack of resonance stabilization compared to a keto form.
2. Structure II: A keto form which generally has greater stability due to strong C=O bond resonance.
3. Structure III: Another enol form, but the presence of conjugation between the double bond and the adjacent carbonyl group offers additional resonance stability compared to Structure I.

Therefore, considering resonance and stabilization factors, the order of stability is given by III > II > I. Here, III is more stable due to extensive conjugation and resonance stabilization, II is a stable keto form, and I is the least stable enol form.

Thus, the correct option is III > II > I.