Question

Can I determine aromaticity by Hückel's rule?

Answer 1

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).

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

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

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

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

the cyclopentadienide anion (`n` = 1).

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