Exams › JEE Main › Chemistry

Why is the cyclopentadienyl anion much more stable than the allyl anion?

1. A cyclic anion is always more stable than an acyclic anion
2. A delocalised anion is more stable than a localised anion
3. The cyclopentadienyl anion is aromatic
4. None of these

Correct answer: The cyclopentadienyl anion is aromatic

Solution

The cyclopentadienyl anion is a planar, cyclic, fully conjugated species with 6 pi electrons (4n+2 with n=1), satisfying Huckel's rule, so it is aromatic and exceptionally stable. The allyl anion is merely delocalized (resonance-stabilized) but not aromatic. The extra aromatic stabilization makes the cyclopentadienyl anion far more stable.

Related JEE Main Chemistry questions

• Arrange the following carbanions in decreasing order of basicity: (A) CH3CH2−, (B) CH2=CH−, and (C) HC≡C−.
• In acid-catalyzed hydration of alkenes, all alkenes except ethene generally give rise to which type of alcohol product?
• Which of the following organic compounds has the same hybridization as the carbon atom in its combustion product, CO2?
• What is formed when CH3MgX reacts with CH3C≡CH?
• Which of the following reagent sets can be used to convert propene into 1-propanol?
• When ethyne (H–C≡CH) is treated first with (1) NaNH2 in liquid NH3 and then with (2) CH3CH2Br, the product X is formed. If X is again subjected to the same two-step sequence, the product Y obtained is:

⚔️ Practice JEE Main Chemistry free + battle 1v1 →