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Q.
Which of the following compounds is not aromatic?
Hydrocarbons
Solution:
Aromaticity of a compound can be decided by Huckel's rule. In cyclopentadienyl cation (b), resonance takes place as follows:
Huckel's rule as it has conjugated $4 \pi$-electron $(4 n \pi, n=1)$ system. Rest of the species are aromatic as each of them belongs to $6 \pi$-electron $[(4 n+2) \pi, n=1]$ system.
