See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Analysis: Which Reaction Gives an Aromatic Product? To identify which reaction yields an aromatic product, we need to consider ring stability and aromaticity requirements (4n+2 π electrons in a planar ring). **Option (a): Cyclopentadienone + $H^+$** - Starting material is a 5-membered ring with one C=O - Addition of $H^+$ would protonate the carbonyl, leading to rearrangement or ring-opening - Does not form a stable aromatic system ✗ **Option (b): Cyclopentanedione + $H^+$** ✓ $$\text{Cyclopentanedione} \xrightarrow{H^+} \text{Cyclopentadienyl cation (5-membered ring, 4π electrons)}$$ - Protonation and loss of water from one carbonyl generates a **cyclopentadienyl cation** - This is a **5-membered aromatic cation** with 4π electrons (4n+2, where n=1) - Forms a stable, aromatic tropylium-like structure - Highly stabilized ✓ **Option (c): Cyclopropylanone + $H^+$** - 3-membered ring ring strain prevents aromaticity - Does not form aromatic product ✗ **Option (d): Cyclobutanedione + $H^+$** - 4-membered ring; would give 4π electrons (antiaromatic, 4n where n=1) - Unstable configuration ✗ **Answer: (b)** — The cyclopentanedione forms the cyclopentadienyl cation, a stable 5-membered aromatic cation with 4π electrons satisfying Hückel's rule.