What aromatic compounds follow Hückel's rule?

1 Answer
Aug 7, 2014

All aromatic compounds follow Hückel's rule.

Explanation:

Hückel's rule states that a planar, cyclic, conjugated molecule is aromatic if it contains 4#n# + 2 π electrons, where #n# = 0 or any positive integer.

See Can I determine aromaticity by Hückel's rule?

Compounds with #n# = 1

The most common examples have #n# = 1. These include

a. Benzene and its derivatives

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b. Six-membered heterocyclics like pyridine and pyrimidine

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c. Five membered heterocyclics like pyrrole, furan, and thiophene

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d. Five-membered anions like cyclopentadienide ion

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e. Seven-membered cations like tropylium ion

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Compounds with #n# = 0

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cyclopropenyl cation

Compounds with #n# = 2

These include naphthalene and azulene.

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Compounds with #n ≥ = 3#

These include the annulenes.

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[14]-annulene (#n# = 3)

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[18]-annulene (#n# = 4)