JEE Chemistry 2026 Question with Solution

Given: Four cyclic carbocations A, B, C and D are shown.

Find: Which cations have the same number of hyperconjugative structures.

Principle: Hyperconjugation in a carbocation depends on the number of available $\beta$-hydrogens on the carbon adjacent to the positively charged carbon. Each $\beta$-hydrogen gives one hyperconjugative structure.

For A, the carbocation is adjacent to a CH$_3$ group, so it has $3$ $\beta$-hydrogens.

For B, the carbocation is adjacent to a CH$_2$ group in the ring, so it has $2$ $\beta$-hydrogens.

For C, the carbocation is adjacent to a CH$_3$ group, so it again has $3$ $\beta$-hydrogens.

For D, the carbocation is adjacent to a CH$_3$ group, so it also has $3$ $\beta$-hydrogens.

Thus, A, C, and D have the same number of hyperconjugative structures, while B does not.

Therefore, the correct option is A.

Given: Hyperconjugation count is required for the four cyclic cations.

Find: The set of cations having equal hyperconjugation.

Use the rule:

1. Identify the carbocation center.
2. Look at the adjacent carbon atom.
3. Count the hydrogens attached to that adjacent carbon.
4. That count equals the number of hyperconjugative structures.

Applying this:

• A $\rightarrow$ adjacent CH$_3$ group $\rightarrow$ $3$ hyperconjugative structures
• B $\rightarrow$ adjacent CH$_2$ group $\rightarrow$ $2$ hyperconjugative structures
• C $\rightarrow$ adjacent CH$_3$ group $\rightarrow$ $3$ hyperconjugative structures
• D $\rightarrow$ adjacent CH$_3$ group $\rightarrow$ $3$ hyperconjugative structures

So the equal counts occur for A, C and D.

Hence, the correct option is A.