What is difference between homonuclear aromatic compounds and heteronuclear aromatic compounds?
Benzene may be the prototypical aromatic molecule, but it is not the only aromatic ring system. According to the IUPAC gold book, any molecule that is cyclic and conjugated that displays resonance stabilization beyond that expected of a delocalized pi system is aromatic.
While experimental confirmation is necessary to verify a molecule's automaticity (e.g. certain NMR behavior, resonance stabilization energy from heats of combustion, or certain reactivity behavior), the Hückel rule gives a good way to predict aromaticity for monocyclic rings systems. In general a monocyclic ring system is aromatic if:
- Has (4n+2) pi electrons, where n is an integer.
Heterocyclic compounds certainly qualify.
Larger and polycyclic systems may be aromatic while appearing to violate the Hückel rule.