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NEET levelSingle correct optionDifficulty 1 of 3g1120

Which of the following is aromatic?

Acyclopentadienyl cation (cyclopenta-2,4-dien-1-ylium)
Bcyclopenta-1,3-diene
Ccyclobutadiene
Dcycloheptatrienyl cation (cyclohepta-2,4,6-trien-1-ylium, tropylium ion)

Answer: D

The tropylium ion is planar with a vacant p orbital on the seventh carbon, so it has 6 pi electrons in a cyclic conjugated array. The cyclopentadienyl cation and cyclobutadiene have 4 pi electrons (antiaromatic) and cyclopenta-1,3-diene has an sp3 carbon and is not fully conjugated.

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