See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Solution: Acidity Order of Four Compounds **Identify the compounds:** - (I) $CH_3-C(=O)-CH_2-C(=O)-CH_3$ — diketone (β-diketone) - (II) $CH_3-C(=O)-CH_3$ — simple ketone (acetone) - (III) $HC \equiv CH$ — alkyne (acetylene) - (IV) $CH_3-CHO$ — aldehyde (acetaldehyde) **Ranking acidity (decreasing order):** 1. **Compound I (most acidic):** The α-hydrogen is highly acidic because the conjugate anion is stabilized by **two adjacent carbonyl groups**. Both carbonyls delocalize the negative charge via resonance, creating a stable enolate ion. 2. **Compound IV:** Aldehyde hydrogens are more acidic than ketone hydrogens due to the more electron-withdrawing nature of the aldehyde group (lower steric hindrance around $C=O$). 3. **Compound II:** Simple ketone with moderate acidity; only one carbonyl to stabilize the enolate. 4. **Compound III (least acidic):** Acetylene's hydrogen has very low acidity (pKa ≈ 25). While acetylenes are weakly acidic due to sp-hybridization, they are far less acidic than carbonyl compounds. **Answer: (a) $I > IV > II > III$** The correct order reflects the stabilization of conjugate anions by electron-withdrawing carbonyl groups and sp-hybridization effects.