# How can you easily identify an aromatic compound?

Well, the Huckel criterion is $\left(4 n + 2\right)$ $\pi \cdot \text{electrons}$
And clearly benzene fulfils this criterion...and so does furan, and so does pyrrole, and so does thiophene. For the heterocycles, the lone pair on the heteroatom is conceived to be delocalized around the ring... Cyclpentadienyl anion, ${C}_{5} {H}_{5}^{-}$ is considered aromatic on this criterion...