See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Hückel's Rule for Aromaticity **Hückel's Rule** states that for a molecule to be aromatic, it must satisfy: 1. **Cyclic structure** 2. **Planar geometry** 3. **Fully conjugated** (continuous p-orbitals) 4. **$(4n+2)$ π electrons** (where $n = 0, 1, 2, 3, ...$) ## Why Option (B) is Correct: The $(4n+2)$ π-electron rule is the **primary electronic criterion** for aromaticity: - $n=0$: 2 electrons (He²⁻, cyclopentadienyl anion) - $n=1$: 6 electrons (benzene) - $n=2$: 10 electrons (naphthalene) - $n=3$: 14 electrons (anthracene) This follows from **molecular orbital theory**: aromatic molecules have all bonding orbitals filled and all antibonding orbitals empty, creating exceptional stability. ## Why Other Options Are Wrong: - **(A) $4n$ π electrons**: This gives antiaromatic molecules (e.g., cyclobutadiene with 4e⁻), which are **unstable** and highly reactive. - **(C) Planar**: While necessary, planarity alone is insufficient—cyclobutadiene is planar but antiaromatic. - **(D) Cyclic**: Cyclicity is required but not sufficient on its own—cyclooctatetraene (8e⁻, antiaromatic) is cyclic but non-planar to avoid antiaromaticity. **Answer: (B)** — $(4n+2)$ π electrons is the definitive electronic requirement for aromaticity.