JEE Chemistry 2025 Question with Solution

Given: Two statements about hyperconjugation and carbocation stabilization are to be checked.

Find: Which option correctly identifies the truth values of Statement I and Statement II.

Hyperconjugation is a stabilizing interaction involving delocalization of $\sigma$-electrons from a C-H or C-C bond to an adjacent empty, partially filled, or $\pi$ orbital.

For Statement I: It says that hyperconjugation is not a permanent effect. The solution states that hyperconjugation is generally considered a permanent effect because this delocalization exists due to orbital overlap present in the bonded structure itself. Therefore, Statement I is false.

For Statement II: A positively charged carbon atom is stabilized by electron donation from adjacent alkyl groups through hyperconjugation. As the number of alkyl groups increases, the number of available $\alpha$-hydrogens generally increases, so hyperconjugative structures increase and the carbocation becomes more stable. Therefore, Statement II is true.

Hence, Statement I is false but Statement II is true.

The correct option is C.

Given:

1. Statement I: Hyperconjugation is not a permanent effect.
2. 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.

Find: Determine the correct option.

Evaluation of Statement I:

• Hyperconjugation is a stabilizing effect caused by delocalization of $\sigma$-electrons.
• It operates in molecules having suitable orbital alignment, such as carbocations, radicals, and alkenes.
• Since this effect is associated with the structure of the molecule itself and does not require an attacking reagent, it is treated as a permanent effect.
• Therefore, Statement I is false.

Evaluation of Statement II:

• In a carbocation, adjacent alkyl groups can donate electron density by hyperconjugation.
• More alkyl groups usually mean more adjacent C-H bonds and more $\alpha$-hydrogens available for hyperconjugative interaction.
• Greater hyperconjugation leads to greater delocalization of positive charge and hence greater carbocation stability.
• Therefore, Statement II is true.

Conclusion: Statement I is false, and Statement II is true. Therefore, the correct option is C.