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JEE Main · 2024 · 30 Jan 2024 · Shift 1 · General Organic Chemistry

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Which of the following molecule/species is most stable?
  1. (A)(see structure)
    ✓ Correct
  2. (B)(see structure)
  3. (C)(see structure)
  4. (D)(see structure)

Answer: (A)

Solution

To determine the most stable species, we need to analyze the aromaticity and electronic structure of each option.

Option (1) shows a benzene anion (cyclohexadienyl anion with negative charge). If this is the cyclopentadienyl anion (C₅H₅⁻), it has:
  • 6 π electrons (satisfies Hückel's rule: 4n+2 = 6, where n=1)
  • Planar, cyclic, and fully conjugated
  • Aromatic and highly stable

Option (2) appears to be a cyclobutadiene cation or similar 4-membered ring cation:
  • Would have 4 π electrons (anti-aromatic if planar)
  • Less stable

Option (3) shows a cycloheptatrienyl anion:
  • Would have 8 π electrons (anti-aromatic, 4n rule)
  • Unstable

Option (4) shows cyclohexadiene (neutral):
  • Not fully conjugated
  • Non-aromatic
  • Less stable than aromatic systems

The cyclopentadienyl anion (option 1) is exceptionally stable due to aromaticity with 6 π electrons, making it the most stable species among the given options.

Therefore, the correct answer is (1).

JEE Main · 2024 · 30 Jan 2024 · Shift 1 · Single correct option

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