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JEE Main 2025 Apr 3 Shift 2, Chemistry Q15: Hyperconjugation

JEE Main2025Apr 3, Shift 2Chemistry
Q.

Given below are two statements :

Statement I : Hyperconjugation is not a permanent effect.

Statement II : In general, greater the number of alkyl groups attached to a positively charged C-atom, greater is the hyperconjugation interaction and stabilization of the cation.

In the light of the above statements, choose the correct answer from the options given below

  1. A

    Statement I is true but Statement II is false

  2. B

    Both Statement I and Statement II are false

  3. C

    Statement I is false but Statement II is true

  4. D

    Both Statement I and Statement II are true

Solution

Hyperconjugation arises from overlap of a bond with an adjacent empty or partially filled p-orbital and does not require any external reagent or stimulus. It is therefore a permanent electronic effect, so Statement I is false.

For carbocations, each -CH bond on an attached alkyl group can donate electron density into the empty p-orbital. More alkyl substituents means more -hydrogens and more hyperconjugative structures, which lowers the cation's energy. This explains the order 3 2 1 CH. Statement II is therefore true.

Statement I is false, Statement II is true, matching option (3).

Concept behind this question

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