See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Cyclooctatetraene (COT) is an 8-membered ring with 4 alternating double bonds (formula C8H8). To assess its structure, we apply Hückel's rule and consider the energetics of planarity. Step 1 - Check aromaticity: For a cyclic conjugated system to be aromatic, it must be planar and have (4n+2) π electrons. COT has 8 π electrons (n=1 gives 6, n=2 gives 10), so 8 = 4n where n=2, making it antiaromatic if planar. Step 2 - Antiaromaticity and planarity: A planar COT would be antiaromatic (8 π electrons, 4n rule), which is highly destabilizing. To avoid antiaromaticity, the molecule distorts out of planarity. Step 3 - Tub (tub-shaped) structure: COT adopts a non-planar, tub-shaped (or tub) conformation. In this geometry, the p-orbitals on adjacent carbons are not parallel, so conjugation is broken, the molecule behaves like a non-conjugated polyene, and antiaromatic destabilization is avoided. This tub shape has been confirmed experimentally by X-ray crystallography and other methods. Step 4 - Why other options fail: (a) Planar structure would force antiaromaticity — not observed. (c) Open chain isomeric structure is not what COT itself has; COT is cyclic. (d) Tautomeric bicyclic structure (bicyclo[4.2.0]octa-2,4,7-triene) is a valence isomer/tautomer that exists in equilibrium with COT at high temperatures, but it is not the primary expected structure of COT itself. Therefore, the correct answer is B.