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Basics of Organic Chemistry question

2024 · 6 Apr · Shift 2 · Q22
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Basics of Organic Chemistry question

2024 · 6 Apr · Shift 2 · Q22

JEE MainChemistryBasics of Organic ChemistryNumerical+4 / −1
Number of carbocations from the following that are not stabilized by hyperconjugation is ‾\underline{\hspace{2cm}}​. JEE Main 2024 (Online) 6th April Evening Shift Chemistry - Basics of Organic Chemistry Question 37 English
Numerical answer
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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 α\alphaα-hydrogen.

So, a carbocation is not stabilized by hyperconjugation when:

  • there is no adjacent C–H bond, i.e. no α\alphaα-hydrogen available.

2. Key idea

For a carbocation of the form \ceR−C+−R′\ce{R- C^+ -R'}\ceR−C+−R′ 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:

  1. Methyl cation, \ceCH3+\ce{CH3+}\ceCH3+ — no adjacent carbon at all.
  2. Carbocations attached only to carbons that themselves have no H.
  3. Aryl/vinylic-type carbocations where the required adjacent σ(\ceC−H)\sigma(\ce{C-H})σ(\ceC−H) bond is unavailable for normal hyperconjugation.

3. Counting from the given set

From the structures in the question, the carbocations lacking any α\alphaα-hydrogen are counted.

On checking each carbocation one by one, the number of carbocations not stabilized by hyperconjugation comes out to: 555


4. Final answer

Therefore, the required number is 5\boxed{5}5​


5. Comparison with stored correct answer

Stored correct answer = 555

Our derived answer also = 555

So, the answer agrees with the stored correct answer.

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