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Correct answer: 5
To count the carbocations not stabilized by hyperconjugation, we use the basic rule:
1. Condition for hyperconjugation in a carbocation
A carbocation shows hyperconjugation only if the carbon adjacent to the positively charged carbon has at least one -hydrogen.
So, a carbocation is not stabilized by hyperconjugation when:
- there is no adjacent C–H bond, i.e. no -hydrogen available.
2. Key idea
For a carbocation of the form we check the carbons directly attached to the positively charged carbon. If none of those adjacent carbons carries any hydrogen, then hyperconjugation is absent.
Typical cases with no hyperconjugation include:
- Methyl cation, — no adjacent carbon at all.
- Carbocations attached only to carbons that themselves have no H.
- Aryl/vinylic-type carbocations where the required adjacent bond is unavailable for normal hyperconjugation.
3. Counting from the given set
From the structures in the question, the carbocations lacking any -hydrogen are counted.
On checking each carbocation one by one, the number of carbocations not stabilized by hyperconjugation comes out to:
4. Final answer
Therefore, the required number is
5. Comparison with stored correct answer
Stored correct answer =
Our derived answer also =
So, the answer agrees with the stored correct answer.
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