NEET 2022 Chemistry Aromaticity & Hückel's Rule MCQ Question

Chapter: Hydrocarbons

Class: 11 | Topic: Aromaticity & Hückel's Rule | Difficulty: 🟡 Moderate

✅ Ans: B — Cycloheptatriene

A compound is aromatic when it is cyclic, planar, fully conjugated and has:

$$(4n+2)\pi\text{ electrons}$$

• A — Cyclopropenyl cation: $2\pi$ electrons → $4(0)+2=2$ → Aromatic ✅
• B — Cycloheptatriene: one carbon is $sp^3$, so conjugation is interrupted → Non-aromatic ❌
• C — Cyclopentadienyl anion: $4+2=6\pi$ electrons → Aromatic ✅
• D — Tropylium cation: $6\pi$ electrons → Aromatic ✅

❌ Why the others are aromatic?

A: $2\pi$ electrons satisfy $4n+2$ → aromatic. C: Lone pair contributes 2 electrons → $6\pi$ → aromatic. D: Positive charge gives an empty $p$-orbital, allowing $6\pi$ delocalisation → aromatic.

📌 NCERT: Aromatic compounds have a planar, cyclic, conjugated system with delocalised $\pi$ electrons.

🧠 NEET Trick: Cyclopropenyl $+$ → 2π | Cyclopentadienyl $−$ → 6π | Tropylium $+$ → 6π | Cycloheptatriene → $sp^3$ carbon → non-aromatic.

Therefore, for the structures exactly as shown in your screenshot, the correct answer should be B, not C.