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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3g1098

Which of the following species are antiaromatic?

Acycloheptatrienyl cation, $C X_{7} H X_{7} X^{+}$
Bcyclopentadienyl cation, $C X_{5} H X_{5} X^{+}$
Ccyclobuta-1,3-diene
Dcyclopropenyl anion, $C X_{3} H X_{3} X^{-}$

Answer: B, C, D

Antiaromatic species are planar, cyclic and fully conjugated with

4 n

π

electrons. Cyclobutadiene (4), the cyclopentadienyl cation (4) and the cyclopropenyl anion (4) qualify. The cycloheptatrienyl cation has 6

π

electrons and is aromatic.

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