Exams › JEE Advanced › Chemistry

Which of the following compounds is NON-aromatic?

1. Cyclopentadiene (five-membered carbocyclic ring with two double bonds and one sp3 CH2 carbon)
2. Thiophene (five-membered ring containing one sulfur atom and two double bonds)
3. Naphthalene (two fused benzene rings)
4. Cyclopentadienyl anion (five-membered ring with two double bonds and a carbanion centre)

Correct answer: Cyclopentadiene (five-membered carbocyclic ring with two double bonds and one sp3 CH2 carbon)

Solution

Cyclopentadiene is non-aromatic because one ring carbon is sp3-hybridised (the CH2 group), disrupting the cyclic conjugation required for aromaticity. The other options — thiophene (6 pi e, lone pair from S), naphthalene (10 pi e), and cyclopentadienyl anion (6 pi e) — are all aromatic.

Related JEE Advanced Chemistry questions

• Even though the chlorination of methane releases energy, why is a high temperature necessary for the reaction to occur?
• Acetylene (HC≡CH) undergoes the following two-step transformation: Step 1: Passed over a red-hot iron tube at 873 K (cyclic trimerisation). Step 2: The product of Step 1 is treated with CO, HCl, and AlCl3 (Gattermann-Koch reaction). How many carbon atoms in the final product are sp2 hybridised?
• Which of the following species is non-aromatic (i.e., neither aromatic nor antiaromatic)?
• Among the following compounds, which one produces ONLY oxalic acid (HOOC-COOH) as the major product when treated with O3 followed by H2O2?
• Which of the following reactions proceeds in the forward direction as written?
• What reagent(s) can convert 1,3-dibromopropane (Br-CH2-CH2-CH2-Br) into acetylene (H-C≡C-H)?

⚔️ Practice JEE Advanced Chemistry free + battle 1v1 →