Can I determine aromaticity by Hückel's rule?

1 Answer
Jul 17, 2014

Yes, you can use Hückel's rule to determine aromaticity.

Hückel's rule says that a planar, conjugated, cyclic molecule is aromatic if it has 4#n#+2 π electrons. The value of #n# can be zero or any positive integer.

The most common aromatic molecule is benzene (#n# =1).

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Azulene is aromatic (#n# = 2). So are heteroaromatic compounds such as pyridine, thiophene, and imidazole (#n# = 1).

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[14]-annulene is aromatic (#n# = 3).

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So is [18]-annulene (#n# = 4).

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Many organic ions are aromatic. These include the cyclopropenyl cation (#n# = 0),

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the cyclopentadienide anion (#n# = 1).

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and the tropylium ion (#n# = 1).

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