Heterocyclic compound: Wikis


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Pyridine, a simple heterocyclic compound

Heterocyclic compounds are organic compounds containing at least one atom of carbon, and at least one element other than carbon, such as sulfur, oxygen or nitrogen within a ring structure.[1] These structures may comprise either simple aromatic rings or non-aromatic rings. Some examples are pyridine (C5H5N), pyrimidine (C4H4N2) and dioxane (C4H8O2).

Note that compounds such as cyclopropane, an anaesthetic with explosive properties, and cyclohexane, a solvent, are not heterocyclic; they are cycloalkanes. The stem '-cyclic' implies a ring structure, whereas 'hetero' refers to an atom other than carbon, as above. Many heterocyclic compounds, including some amines, are carcinogenic.

Heterocyclic chemistry is the chemistry branch dealing exclusively with synthesis, properties, and applications of heterocycles. The IUPAC recommends using the Hantzsch-Widman nomenclature to name heterocyclic compounds.


3-Membered rings

Heterocycles with three atoms in the ring are more reactive because of ring strain. Those containing one heteroatom are, in general, stable. Those with two heteroatoms are more likely to occur as reactive intermediates. Common 3-membered heterocycles are:

Heteroatom Saturated Unsaturated
Nitrogen Aziridine Azirine
Oxygen Ethylene oxide (epoxides, oxiranes) Oxirene
Sulfur Thiirane (episulfides) Thiirene

Those with two heteroatoms include:

Heteroatom Saturated Unsaturated
Oxygen Dioxirane
Nitrogen Diazirine

4-Membered rings

Compounds with one heteroatom:

Heteroatom Saturated Unsaturated
Nitrogen Azetidine Azete
Oxygen Oxetane Oxete
Sulfur Thietane Thiete

Compounds with two heteroatoms:

Heteroatom Saturated Unsaturated
Nitrogen Diazetidine
Oxygen Dioxetane Dioxetene
Sulfur Dithietane Dithiete

5-Membered rings

With heterocycles containing five atoms, the unsaturated compounds are frequently more stable because of aromaticity.

Five-membered rings with a single heteroatom:

Heteroatom Saturated Unsaturated
Nitrogen Azolidine Azole
Oxygen Oxolane Oxole
Sulfur Thiolane Thiole
Phosphorus Phospholane Phosphole
Silicon Sillane Silole
Arsenic Arsolane Arsole

The 5-membered ring compounds containing two heteroatoms, at least one of which is nitrogen, are collectively called the azoles. Thiazoles and isothiazoles contain a sulfur and a nitrogen atom in the ring. Dithiolanes have two sulfur atoms.

Heteroatom Saturated Unsaturated
Nitrogen Imidazolidine
Nitrogen/oxygen Oxazolidine
Nitrogen/sulfur Thiazolidine
Oxygen Dioxolane
Oxygen/sulfur Oxathiolane
Sulfur Dithiolane

A large group of 5-membered ring compounds with three heteroatoms also exists. One example is dithiazoles that contain two sulfur and a nitrogen atom.

Heteroatom Saturated Unsaturated
Nitrogen Triazoles
Nitrogen/2-sulfur Dithiazole
2-Nitrogen/oxygen Furazan
2-Nitrogen/sulfur Thiadiazole

Five-member ring compounds with four heteroatoms:

Heteroatom Saturated Unsaturated
Nitrogen Tetrazole

With 5-heteroatoms, the compound may be considered inorganic rather than heterocyclic. Pentazole is the all nitrogen heteroatom unsaturated compound.

6-Membered rings

Six membered rings with a single heteroatom:

Heteroatom Saturated Unsaturated
Nitrogen Piperidine Pyridine
Oxygen Tetrahydropyran Pyran
Sulfur Thiane Thiopyran

With two heteroatoms:

Heteroatom Saturated Unsaturated
Nitrogen Piperazine Diazines
Nitrogen / oxygen Morpholine Oxazine
Nitrogen / sulfur Thiazine
Sulfur Dithiane
Oxygen Dioxane Dioxin

With three heteroatoms:

Heteroatom Saturated Unsaturated
Nitrogen Triazine
Oxygen Trioxane

With four heteroatoms:

Heteroatom Saturated Unsaturated
Nitrogen Tetrazine

The hypothetical compound with six nitrogen heteroatoms would be hexazine.

7-Membered rings

With 7-membered rings, aromatic stabilization is not available. Compounds with one heteroatom include:

Heteroatom Saturated Unsaturated
Nitrogen Azepane Azepine
Oxygen Oxepane Oxepine
Sulfur Thiepane Thiepine

Those with two heteroatoms include:

Heteroatom Saturated Unsaturated
Nitrogen Diazepine
Nitrogen/sulfur Thiazepine

8-Membered rings

Compounds with one heteroatom include:

Heteroatom Saturated Unsaturated
Nitrogen Azocane Azocine
Oxygen Oxecane
Sulfur Thiocane


Saturated Unsaturated
Heteroatom Nitrogen Oxygen Sulfur Nitrogen Oxygen Sulfur
Name Aziridine Oxirane Thiirane Azirine Oxirene Thiirene
Structure Struktur von Aziridin Struktur von Oxiran Struktur von Thiiran Struktur von Azirin Struktur von Oxiren Struktur von Thiiren
Name Azetidine Oxetane Thietane Azete Oxete Thiete
Structure Struktur von Azetidin Struktur von Oxetan Struktur von Thietan Struktur von Azet Struktur des Oxetiumions Struktur des Thietiumions
Name Pyrrolidine Tetrahydrofuran Tetrahydrothiophene Pyrrole Furan Thiophene
Structure Struktur von Pyrrolidin Struktur von Tetrahydrofuran Struktur von Tetrahydrothiophen Struktur von Pyrrol Struktur von Furan Struktur von Thiophen
Name Piperidine Tetrahydropyran Thiane Pyridine Pyrylium Thiopyran
Structure Struktur von Piperidin Struktur von Tetrahydropyran Struktur von Tetrahydrothiopyran Struktur von Pyridin Struktur des Pyryliumions Struktur des Thiopyryliumions
Name Azepane Oxepane Thiepane Azepine Oxepine Thiepine
Structure Struktur von Azepan Struktur von Oxepan Struktur von Thiepanan Struktur von Azepin Struktur von Oxepin Struktur von Thiepin

Fused rings

Heterocyclic rings systems that are formally derived by fusion with other rings, either carbocyclic or heterocyclic, have a variety of common and systematic names. For example, with the benzo-fused unsaturated nitrogen heterocycles, pyrrole provides indole or isoindole depending on the orientation. The pyridine analog is quinoline or isoquinoline. For azepine, benzazepine is the preferred name. Similarly, the compounds with two benzene rings fused to the central heterocycle are carbazole, acridine, and dibenzoazepine.


  1. ^ Eicher, T.; Hauptmann, S. (2nd ed. 2003). The Chemistry of Heterocycles: Structure, Reactions, Syntheses, and Applications. Wiley-VCH. ISBN 3527307206. 

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