How do you identify aromatic rings?

1 Answer
Aug 29, 2016

Answer:

An aromatic ring must be a planar, cyclic, system containing (4n + 2) π electrons in alternating single and double bonds with no intervening saturated carbon atoms.

Explanation:

Hückel's rule states that an aromatic system must have (#4n + 2#) π electrons (#n = 0, 1, 2 ,3, 4, …)

Examples

Thus, benzene is aromatic because it satisfies Hückel's rule.

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#4n+ 2 = 6#

#n = 1#

The cyclopropenyl cation is also aromatic.

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#4n + 2 = 2#

# n= 0#

A ring with 4 pi electrons is not aromatic

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#4n + 2 = 4#

#n = 2/4 = 1/2#

n is a fraction.

Thus, cyclobutadiene doesn't follow Hückel's rule and is not aromatic.