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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3hc219

Which of the following species are aromatic (planar, cyclic, fully conjugated, $(4 n + 2)$ pi electrons)?

ACyclopropenyl cation
BCycloheptatrienyl (tropylium) cation
CCyclopentadienyl cation
DCyclopentadienyl anion

Answer: A, B, D

Count the pi electrons: cyclopropenyl cation 2, tropylium cation 6 and cyclopentadienyl anion 6, all

4 n + 2

. The cyclopentadienyl cation has 4 pi electrons (

4 n

), so it is antiaromatic.

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