Simple aromatic ring


Simple aromatic rings, also known as simple arenes or simple aromatics, are aromatic organic compounds that consist only of a conjugated planar ring system. Many simple aromatic rings have trivial names. They are usually found as substructures of more complex molecules. Typical simple aromatic compounds are benzene, indole, and pyridine.
Simple aromatic rings can be heterocyclic if they contain non-carbon ring atoms, for example, oxygen, nitrogen, or sulfur. They can be monocyclic as in benzene, bicyclic as in naphthalene, or polycyclic as in anthracene. Simple monocyclic aromatic rings are usually five-membered rings like pyrrole or six-membered rings like pyridine. Fused aromatic rings consist of monocyclic rings that share their connecting bonds.

Heterocyclic aromatic rings

The nitrogen -containing aromatic rings can be separated into basic aromatic rings that are easily protonated, and form aromatic cations and salts, and non-basic aromatic rings.
In the oxygen- and sulfur-containing aromatic rings, one of the electron pairs of the heteroatoms contributes to the aromatic system, whereas the second lone pair extends in the plane of the ring.

Criteria for aromaticity

In contrast, molecules with 4n pi electrons are antiaromatic.