MCQMediumJEE 2023Electronic Effects (Inductive, Resonance, Hyperconjugation)

JEE Chemistry 2023 Question with Solution

Given below are two statements: Statement I: Tropolone is an aromatic compound and has 8π8\pi electrons. Statement II: The bond angle of C=O\text{C} = \text{O} group in tropolone is involved in aromaticity.

  • A

    Statement I is false but Statement II is true

  • B

    Statement I is true but Statement II is false

  • C

    Both Statement I and Statement II are true

  • D

    Both Statement I and Statement II are false

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: Two statements about tropolone are to be checked.

Find: Which statement is correct.

For Statement I, the solution explains that tropolone is an aromatic compound with a conjugated ring system containing 8π8\pi electrons. It states that 6π6\pi electrons are endocyclic and 2π2\pi electrons from the >C=O>\text{C}=\text{O} group are exocyclic. Therefore, Statement I is correct.

For Statement II, the solution explains that the π\pi electrons of the >C=O>\text{C}=\text{O} group are exocyclic and do not contribute to the conjugated ring system responsible for aromaticity. Therefore, Statement II is incorrect.

Hence, the conclusion from the solution is: Statement I is true but Statement II is false.

Although the solution marks the correct option as C, the written conclusion clearly matches option B. Therefore, the defensible correct option is B.

Common mistakes

  • Counting the exocyclic π\pi electrons of the C=O\text{C}=\text{O} group as if they directly participate in ring aromaticity is incorrect. Exocyclic electrons are not treated the same way as endocyclic ring electrons for aromatic stabilization. Focus on the conjugated cyclic system separately.

  • Confusing bond angle involvement with electron delocalization is a conceptual mistake. Aromaticity depends on cyclic conjugation and overlap of pp orbitals, not on the bond angle of the carbonyl group by itself.

  • Relying only on the option label shown in the solution can lead to error here. The detailed written explanation concludes that Statement I is true and Statement II is false, which corresponds to option B. Always trust the worked conclusion over a mismatched label.

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