See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Identifying the Non-Aromatic Compound **Aromaticity Criteria (Hückel's Rule):** A compound is aromatic if it has $(4n+2)$ π electrons in a cyclic, planar, conjugated system. --- **Analyzing each species:** **(I) Indene (7-membered + 5-membered fused ring):** - Has 10 π electrons in a conjugated system - $10 = 4(2) + 2$ → **Aromatic** ✓ **(II) Cyclopropane cation ($C_3H_3^+$):** - Has 2 π electrons (from one double bond equivalent) - $2 = 4(0) + 2$ → **Aromatic** (very stable) ✓ **(III) Cyclobutadiene dication ($C_4H_4^{2+}$):** - Originally has 4 π electrons (antiaromatic) - Removing 2 electrons leaves 2 π electrons - $2 = 4(0) + 2$ → **Aromatic** ✓ **(IV) [8]Annulene (10-membered ring):** - Has 10 π electrons: $10 = 4(2) + 2$ - However, the structure is **not planar** — steric strain from inner hydrogen atoms forces the ring into a non-planar conformation - Cannot satisfy aromaticity without planarity - **Non-aromatic** ✗ --- **Answer: (D) IV** — [8]Annulene lacks planarity despite having the correct electron count, violating a fundamental aromaticity requirement.