See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Acid Dissociation Constant Analysis **Key Principle:** Larger $K_a$ means stronger acid (more easily donates proton from C-H adjacent to carbonyl). **Structure Analysis:** **(A) Cyclohexanone:** One ketone group - Single $\alpha$-hydrogen adjacent to $C=O$ - Moderate acidity **(B) Cyclohexane-1,4-dione:** Two ketone groups in para positions - $\alpha$-hydrogens are isolated from each carbonyl - Weak acidity (no conjugation between carbonyls) **(C) Cyclohexane-1,3-dione:** Two ketone groups in meta positions - $\alpha$-CH₂ is flanked by TWO electron-withdrawing carbonyls - Enolate anion is **doubly stabilized** by resonance with both carbonyls - Highest acidity **(D) Cyclohexane-1,2-dione:** Two ketone groups (ortho) - Adjacent carbonyls create steric hindrance - Less effective stabilization of enolate **Why C has largest $K_a$:** The $\alpha$-CH₂ in compound (C) loses a proton to form an enolate that is stabilized by resonance delocalization with **both adjacent carbonyl groups**. This dual stabilization makes the conjugate base most stable, making the original compound most acidic. $$K_a \text{ is largest when conjugate base is most stable} \rightarrow \text{**Option (C)**}$$