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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3g1151

Which of the following carbocations are stabilised by BOTH hyperconjugation and resonance?

A $C X_{6} H X_{5} - CH X^{+} - CH X_{3}$
B $CH X_{2} = CH - CH X^{+} - CH X_{3}$
C $(CH X_{3}) X_{3} C X^{+}$
D $CH X_{2} = CH - CH X_{2} X^{+}$

Answer: A, B

Resonance needs an adjacent pi bond or ring; hyperconjugation needs an alpha sp3 C-H.

C X_{6} H X_{5} CH X^{+} CH X_{3}

and

CH X_{2} = CH - CH X^{+} - CH X_{3}

have both.

(CH X_{3}) X_{3} C X^{+}

has only hyperconjugation and the allyl cation

CH X_{2} = CH - CH X_{2} X^{+}

has only resonance.

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