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
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
Show Hint
- Statement I is true but Statement II is false
- Both Statement I and Statement II are false
- Statement I is false but Statement II is true
- Both Statement I and Statement II are true
The Correct Option is C
Approach Solution - 1
To determine the correctness of the given statements, we need to evaluate each statement based on the concepts of organic chemistry:
Evaluation of Statement I
- Definition of Hyperconjugation: Hyperconjugation is a stabilizing interaction that involves the delocalization of electrons from a sigma bond (usually C-H or C-C) to an adjacent empty or partially filled p-orbital or a π-bond.
- Nature of Hyperconjugation: Contrary to Statement I, hyperconjugation is generally considered a permanent effect because it involves the overlap of orbitals that are always present as long as the molecule remains bonded in the same configuration. Therefore, Statement I is false.
Evaluation of Statement II
- Electronics Influence on Cations: As more alkyl groups are attached to a positively charged carbon atom (cation), there will be more hyperconjugative structures contributing to stabilize the cation.
- Reasoning: Alkyl groups can donate electron density through hyperconjugation, which stabilizes the positive charge on the carbon atom. Hence, the more alkyl groups, the greater the hyperconjugation stabilization. Thus, Statement II is true.
Conclusion
- Based on the evaluations, Statement I is false but Statement II is true.
Approach Solution -2
Statement I : Hyperconjugation is not a permanent effect. Hyperconjugation is a permanent effect that involves the delocalization of \( \sigma \)-electrons of a C-H bond of an alkyl group directly attached to an unsaturated system or to an atom with an unshared p-orbital.
This delocalization occurs even in the absence of an external reagent or condition.
Therefore, Statement I is false. 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.
A carbocation is stabilized by hyperconjugation due to the donation of \( \sigma \)-electrons from the adjacent C-H bonds. Alkyl groups attached to the positively charged carbon atom have C-H bonds that can participate in hyperconjugation. The more alkyl groups attached, the greater the number of \( \alpha \)-hydrogen atoms available for hyperconjugation.
This leads to greater delocalization of the positive charge and hence greater stability of the carbocation.
Therefore, Statement II is true. In conclusion, Statement I is false, but Statement II is true. This corresponds to option (3).
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