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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3g3054

Select the correct comparison(s) of carbocation stability.

A $CH X_{2} = CH X^{+} > CH X_{3} CH X_{2} X^{+}$
B $(C X_{6} H X_{5}) X_{3} C X^{+} > (C X_{6} H X_{5}) X_{2} CH X^{+}$
Ccyclohepta-2,4,6-trien-1-ylium (tropylium) $>$ $C X_{6} H X_{5} CH X_{2} X^{+}$
D $p - CH X_{3} O - C X_{6} H X_{4} - CH X_{2} X^{+} > C X_{6} H X_{5} CH X_{2} X^{+}$

Answer: B, C, D

More aryl groups give more resonance stabilisation, and p-methoxy adds a lone-pair (

+ M

) donation. Tropylium is aromatic and is more stable than benzyl. The vinyl cation, with the charge on an

s p

carbon and no hyperconjugation or resonance, is less stable than the ethyl cation, so the third is false.

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