Containing more than one kind of atom joined in a ring.
heterocycle het'er·o·cy'cle (-sī'kəl) n.heterocyclic het'er·o·cy'clic n.
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het·er·o·cy·clic (hĕt'ə-rō-sī'klĭk, -sĭk'lĭk) ![]() |
Containing more than one kind of atom joined in a ring.
heterocycle het'er·o·cy'cle (-sī'kəl) n.| 5min Related Video: heterocyclic |
| Sci-Tech Encyclopedia: Heterocyclic compounds |
Cyclic compounds in which the rings include at least one atom of an element different from the rest. Most types of heterocyclic compounds studied to date are organic compounds. An example of an organic heterocyclic compound is oxazoline (1); an example of an inorganic heterocyclic compound is the phosphonitrilic chloride (2). The smallest possible ring is three-membered, for example, ethylene oxide (3), but very 1




Naturally occurring heterocyclic compounds are extremely common as, for example, most alkaloids, sugars, vitamins, DNA and RNA, enzymic cofactors, plant pigments, many of the components of coal tar, many natural pigments (such as indigo, chlorophyll, hemoglobin, and the anthocyanins), antibiotics (such as penicillin and streptomycin), and some of the essential amino acids (for example, tryptophan), and many of the peptides (such as oxytocin). Some of the most important naturally occurring high polymers are heterocyclic, including starch and cellulose. The major groups of natural products that are not mainly heterocyclic are the fats and most of the terpenes, steroids, and essential α-amino acids, though exceptions do exist.
Heterocyclic compounds may be named systematically. Many heterocycles, however, have nonsystematic names that are usually preferred by practicing chemists over the systematic ones. In the systematic approach to nomenclature the ring size is denoted by the appropriate stem. For example, three-membered saturated rings without nitrogen would have a name ending in -irane. The nature of the heteroatom is denoted by such prefixes as oxa-, thia-, or aza-, for oxygen, sulfur, or nitrogen, respectively. Thus, ethylene oxide (3) becomes oxirane. A five-membered unsaturated ring would have a name ending in -ole. A six-membered unsaturated ring containing nitrogen would have a name ending in -ine according to this scheme. Actually, the trivial names for many systems are commonly accepted, and the systematic names are not often used.
For details about specific heterocyclic systems See also Furan; Heterocyclic polymer; Indole; Pyridine; Pyrimidine; Pyrrole.
| Britannica Concise Encyclopedia: heterocyclic compound |
For more information on heterocyclic compound, visit Britannica.com.
| Veterinary Dictionary: heterocyclic |
Having or pertaining to a closed chain or ring formation that includes atoms of different elements.
| Wikipedia: 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.
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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 |
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 |
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 | Pyrrolidine | Pyrroline Pyrrole |
| Oxygen | Tetrahydrofuran | Dihydrofuran Furan |
| Sulfur | Tetrahydrothiophene | Dihydrothiophene Thiophene |
| Phosphorus | Phosphole | |
| Silicon | Silole | |
| Arsenic | 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 Pyrazolidine |
Imidazole Imidazoline Pyrazole Pyrazoline |
| Nitrogen/oxygen | Oxazolidine Isoxazolidine |
Oxazole Oxazoline Isoxazole Isoxazoline |
| Nitrogen/sulfur | Thiazolidine Isothiazolidine |
Thiazole Thiazoline Isothiazole Isothiazoline |
| 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 Oxadiazole |
|
| 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.
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.
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 |
Compounds with one heteroatom include:
| Heteroatom | Saturated | Unsaturated |
|---|---|---|
| Nitrogen | Azocane | Azocine |
| Oxygen | Oxecane | |
| Sulfur | Thiocane |
| Saturated | Unsaturated | ||||||
|---|---|---|---|---|---|---|---|
| Heteroatom | Nitrogen | Oxygen | Sulfur | Nitrogen | Oxygen | Sulfur | |
| 3-Ring | |||||||
| Name | Aziridine | Oxirane | Thiirane | Azirine | Oxirene | Thiirene | |
| Structure | |||||||
| 4-Ring | |||||||
| Name | Azetidine | Oxetane | Thietane | Azete | Oxete | Thiete | |
| Structure | |||||||
| 5-Ring | |||||||
| Name | Pyrrolidine | Tetrahydrofurane | Tetrahydrothiophene | Pyrrole | Furan | Thiophene | |
| Structure | |||||||
| 6-Ring | |||||||
| Name | Piperidine | Tetrahydropyran | Thiane | Pyridine | Pyrylium | Thiopyran | |
| Structure | |||||||
| 7-Ring | |||||||
| Name | Azepane | Oxepane | Thiepane | Azepine | Oxepine | Thiepine | |
| Structure | |||||||
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.
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| What is the nomenclature of heterocyclic compound? | |
| Why heterocycle compounds aromatic? |
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