Simple aromatic ring

Simple aromatic rings, also known as simple arenes or simple aromatics, are indole.

Simple aromatic rings can be pyridine. Fused aromatic rings consist of monocyclic rings that share their connecting bonds.

Heterocyclic aromatic rings

The nitrogen (N)-containing aromatic rings can be separated into salts (e.g., pyridinium), and non-basic aromatic rings.

• In the basic aromatic rings, the purine.

• In the non-basic rings, the lone pair of electrons of the nitrogen atom is delocalized and contributes to the aromatic pi electron system. In these compounds, the nitrogen atom is connected to a hydrogen atom. Examples of non-basic nitrogen-containing aromatic rings are indole.

In the oxygen- and sulfur-containing aromatic rings, one of the electron pairs of the heteroatoms contributes to the aromatic system (similar to the non-basic nitrogen-containing rings), whereas the second lone pair extends in the plane of the ring (similar to the basic nitrogen-containing rings).

Criteria for Aromaticity

Main article: Aromaticity

• Molecule must be cyclic.
• Every atom in the ring must have a conjugated).
• Molecule must be planar.
• It must contain an odd number of pairs of pi electrons; must satisfy Huckel's rule: (4n+2) pi electrons, where n is an integer starting at zero.

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

See also

• Polycyclic aromatic compounds
• Polycyclic aromatic hydrocarbons (PAH)