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 ("substituted aromatics"). Typical simple aromatic compounds are benzene, indole, and cyclotetradecaheptaene.[1][2]

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

Table of simple aromatic rings

Furan

Benzofuran

Isobenzofuran

Pyrrole

Indole

Isoindole

Thiophene

Benzothiophene

Benzo[c]thiophene

Imidazole

Benzimidazole

Purine

Pyrazole

Indazole
 

Oxazole

Benzoxazole
 

Isoxazole

Benzisoxazole
 

Thiazole

Benzothiazole
 
 
Six-membered rings and  Fused six-membered rings  

Benzene

Naphthalene

Anthracene

Pyridine

Quinoline

Isoquinoline

Pyrazine

Quinoxaline

Acridine

Pyrimidine

Quinazoline
 

Pyridazine

Cinnoline

Phthalazine

1,2,3-Triazine

1,2,4-Triazine

1,3,5-Triazine
(s-triazine)

The nitrogen (N)-containing aromatic rings can be separated into basic aromatic rings that are easily protonated, and form aromatic cations and salts (e.g., pyridinium), 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 (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

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

See also

References

  1. Clayden, J.; Greeves, N.; Warren, S.; Wothers, P. (2001). Organic Chemistry. Oxford, Oxfordshire: Oxford University Press. ISBN 0-19-850346-6.
  2. Eicher, T.; Hauptmann, S. (2003). The Chemistry of Heterocycles: Structure, Reactions, Syntheses, and Applications (2nd ed.). Wiley-VCH. ISBN 3-527-30720-6.
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