Which of the following species is not aromati | vedclass

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(B) To determine if a species is aromatic,it must follow $H$ückel's rule: it must be cyclic,planar,fully conjugated,and contain $(4n + 2) \pi$ electro

Vedclass · Accepted Answer

Cyclopentadienyl cation $(C_5H_5^+)$

Vedclass · Answer

(B) To determine if a species is aromatic,it must follow $H$ückel's rule: it must be cyclic,planar,fully conjugated,and contain $(4n + 2) \pi$ electrons,where $n = 0, 1, 2, ...$.$A$. Cyclopentadienyl anion $(C_5H_5^-)$: It has $6 \pi$ electrons ($4$ from double bonds + $2$ from the lone pair),which follows $(4n + 2)$ with $n = 1$. It is aromatic.$B$. Cyclopentadienyl cation $(C_5H_5^+)$: It has $4 \pi$ electrons. According to $H$ückel's rule,species with $4n \pi$ electrons are anti-aromatic. Thus,it is not aromatic.$C$. Cyclopropenyl cation $(C_3H_3^+)$: It has $2 \pi$ electrons,which follows $(4n + 2)$ with $n = 0$. It is aromatic.$D$. Tropylium cation $(C_7H_7^+)$: It has $6 \pi$ electrons,which follows $(4n + 2)$ with $n = 1$. It is aromatic.Therefore,the cyclopentadienyl cation is not aromatic.

Which of the following species is not aromatic?

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