Heterocyclic compound

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Heterocyclic compound

Heterocyclic compounds are organic compound

Organic compound

An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered Inorganic compound....
s containing at least one atom of carbon

Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
, and at least one element other than carbon, such as sulfur

Sulfur

Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant Valence non-metal....
, oxygen

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
or nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
within a ring structure. These structures may comprise either simple aromatic ring

Simple aromatic ring

Simple aromatic rings, also known as simple arenes or simple aromatics, are aromatic organic compounds that consist only of a conjugated system planar ring system with delocalized_electron pi electron clouds....
s or non-aromatic rings. Some examples are pyridine

Pyridine

Pyridine is a simple and important heterocyclic aromatic organic compound with the formula CarbonHydrogenNitrogen. This colorless liquid with a distinctive fish-like odor is structurally related to benzene, wherein one CH group in the six-membered ring is replaced by a nitrogen atom....
(C₅H₅N), pyrimidine

Pyrimidine

Pyrimidine is a heterocyclic aromatic organic compound similar to benzene and pyridine, containing two nitrogen atoms at positions 1 and 3 of the six-member ring....
(C₄H₄N₂) and dioxane (C₄H₈O₂).

Note that compounds such as cyclopropane
Cyclopropane

Cyclopropane is a cycloalkane molecule with the molecular formula C3H6, consisting of three carbon atoms linked to each other to form a ring, with each carbon atom bearing two hydrogen atoms....
, an anaesthetic with explosive properties, and cyclohexane
Cyclohexane

Cyclohexane is a cycloalkane with the molecular formula Carbon6Hydrogen12. Cyclohexane is used as a nonpolar solvent for the chemical industry, and also as a raw material for the industrial production of adipic acid and caprolactam, both of which are intermediates used in the production of nylon....
, a solvent, are not heterocyclic; they are merely cycloalkanes.

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Encyclopedia

Heterocyclic compounds are organic compound

Organic compound

Carbon

Sulfur

Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant Valence non-metal....
, oxygen

Oxygen

Nitrogen

Simple aromatic ring

Pyridine

Pyrimidine

Amine

Amines are organic compounds and functional groups that contain a base nitrogen atom with a lone pair. Amines are derivative s of ammonia, wherein one or more hydrogen atoms are replaced by organic substituents such as alkyl and aryl groups....
s, are carcinogenic.

Heterocyclic chemistry is the chemistry branch dealing exclusively with synthesis, properties, and applications of heterocycles. IUPAC name is Hantzsch-Widman nomenclature.

3-Membered rings

Heterocycles with three atoms in the ring are more reactive because of ring strain

Ring strain

Ring strain is an organic chemistry term that describes the destabilization of a cyclic molecule?such as a cycloalkane?due to the non-favorable high energy Molecular geometry of its atoms....
. 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 Aziridine Aziridines are a group of organic compounds sharing the aziridine functional group which is a three membered heterocycle with one amine group and two methylene groups....	Azirine
Oxygen	Ethylene oxide Ethylene oxide Ethylene oxide is the organic compound with the chemical formula C2H4O. This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom.... (epoxide Epoxide An epoxide is a cyclic ether with only three ring atoms. This ring approximately is an equilateral triangle which makes it highly ring strain.... s, oxiranes)	Oxirene
Sulfur	Thiirane Thiirane Thiirane, more commonly known as ethylene sulfide, is the cyclic chemical compound with the formula C2H4S. It is the smallest sulfur-containing heterocycle.... (episulfide Episulfide Episulfides are a class of organic compounds that contain a Saturation heterocycle consisting of two carbon atoms and one sulfur atom. It is the sulfur analogue of an epoxide or aziridine. The parent episulfide is thiirane.... s)

Those with two heteroatoms include:

Heteroatom	Saturated	Unsaturated
Oxygen	Dioxirane Dioxirane A dioxirane is a molecule containing a three-membered ring composed of one carbon and two oxygens. Somewhat unstable, they are used in organic synthesis as oxidizing reagents....

4-Membered rings

Compounds with one heteroatom:

Heteroatom	Saturated	Unsaturated
Nitrogen	Azetidine Azetidine Azetidine is a heterocyclic organic compound. It belongs to the class of four membered rings and it contains a nitrogen atom....
Oxygen	Oxetane Oxetane Oxetane is the heterocycle organic compound having a four-membered ring with three carbon atoms and one oxygen atom with the molecular formula C3H6O....
Sulfur	Thietane

Compounds with two heteroatoms:

Heteroatom	Saturated	Unsaturated
Oxygen	Dioxetane Dioxetane Dioxetanes are heterocyclic compound organic compounds which consist of a four-membered ring that contains two oxygen atoms and two carbon atoms....
Sulfur	Dithietane Dithietane Dithietanes are saturated heterocyclic compounds that contain two sulfur atoms and two sp3-hybridized carbon centers. Two isomers are possible for this class of organosulfur compounds, 1,2-dithietanes, where the sulfur atoms are adjacent, and 1,3-dithietanes, where the sulfur atoms are not adjacent....	Dithiete Dithiete Dithietes are unsaturated heterocyclic compounds that contain two sulfur atoms and two sp2-hybridized carbon centers. Having 6-pi electrons, dithietes are aromaticity....

5-Membered rings

With heterocycles containing five atoms, the unsaturated compounds

Unsaturated compound

In organic chemistry, an unsaturated compound is a chemical compound that contains carbon-carbon double bonds or triple bonds such as in alkenes or alkynes....
are frequently more stable because of aromaticity

Aromaticity

Aromaticity is a chemical property in which a conjugated system ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone....
.

Five-membered rings with a single heteroatom:

Heteroatom	Saturated	Unsaturated
Nitrogen	Tetrahydropyrrole (azolidine, pyrrolidine Pyrrolidine Pyrrolidine, also known as tetrahydropyrrole, is an organic compound with the molecular formula C4H9N. It is a cyclic amine with a five-membered ring containing four carbon atoms and one nitrogen atom.... )	Dihydropyrrole (pyrroline Pyrroline Pyrrolines, also known under the name dihydropyrroles, are three different heterocyclic compound organic chemistry chemical compounds which differ in the position of the double bond.... ), Pyrrole Pyrrole Pyrrole, or pyrrol, is a heterocyclic aromatic organic compound, a five-membered ring with the chemical formula carbon4hydrogen4nitrogenH....
Oxygen	Tetrahydrofuran Tetrahydrofuran Tetrahydrofuran is a colorless, water-miscible organic liquid with low-viscosity at "room" temperature and pressure . It is a Heterocyclic compound compound with a chemical formula C4H8O, and is the fully Hydrogenation analog of the aromatic organic compound furan.... (oxolane)	Dihydrofuran, Furan Furan Furan, also known as furane and furfuran, is a Heterocyclic compound organic compound. It is typically derived by the thermal decomposition of pentose-containing materials, cellulosic solids especially pine-wood....
Sulfur	Tetrahydrothiophene Tetrahydrothiophene Tetrahydrothiophene is a heterocyclic organic compound consisting of a five-membered ring containing four carbon atoms and a sulfur atom. It is the saturation analog of thiophene.... (thiolane)	Dihydrothiophene, Thiophene Thiophene Thiophene is the heterocyclic compound with the formula C4H4S. Consisting of a flat five-membered ring, it is aromaticity as indicated by its extensive substitution reactions....
Arsenic		Arsole Arsole Arsole, rarely called arsenole, is a cyclic organoarsenic chemical compound of the chemical formula C4H5As. The structure is isoelectronic to that of pyrrole except that an arsenic atom is substituted for the nitrogen atom....

The 5-membered ring compounds containing two heteroatoms, at least one of which is nitrogen, are collectively called the azole

Azole

An azole is a class of five-membered nitrogen heterocyclic ring compounds containing at least one other noncarbon atom, nitrogen, sulfur or oxygen....
s. Thiazole

Thiazole

Thiazole, or 1,3-thiazole, is a clear to pale yellow flammable liquid with a pyridine-like odor and the molecular formula C3H3NS....
s and isothiazole

Isothiazole

An isothiazole is a type of organic compound containing a five-membered aromatic ring that consists of three carbon atoms, one nitrogen atom, and one sulfur atom....
s contain a sulfur and a nitrogen atom in the ring. Dithiolane

Dithiolane

A dithiolane is a sulfur heterocyclic compound derived from cyclopentane by replacing two methylene groups with thioether groups. The parent compounds are 1,2-dithiolane and 1,3-dithiolane....
s have two sulfur atoms.

Heteroatom	Saturated	Unsaturated
Nitrogen	Imidazolidine Imidazolidine Imidazolidine is a heterocyclic compound formally derived by the addition of four hydrogen atoms to imidazole. The intermediate, resulting from the addition of only two hydrogen atoms is called dihydroimidazole....	Pyrazole Pyrazole Pyrazole refers both to the class of simple aromatic ring organic compounds of the heterocyclic series characterized by a 5-membered ring structure composed of three carbon atoms and two nitrogen atoms in adjacent positions and to the unsubstituted parent compound.... , Imidazole Imidazole Imidazole is a organic compound with the formula C3H4N2. This aromatic heterocyclic is classified as an alkaloid....
Nitrogen/oxygen	Oxazolidine Oxazolidine Oxazolidine is a five-membered ring compound consisting of three carbons, a nitrogen, a hydrogen, and an oxygen. The oxygen and NH are the 1 and 3 positions, respectively....	Oxazole Oxazole Oxazole is the parent compound for a vast class of heterocyclic compound aromatic organic compounds. These are azoles with an oxygen and a nitrogen separated by one carbon.... , Isoxazole Isoxazole Isoxazole is an azole with an oxygen atom next to the nitrogen.Isoxazoles are found in some natural products, such as ibotenic acid. Isoxazoles also form the basis for a number of drugs, including the COX-2 inhibitor valdecoxib ....
Nitrogen/sulfur	Thiazolidine Thiazolidine Thiazolidines are a class of heterocyclic organic compounds with a 5-membered saturation ring with an amine group and a thioether group in the 1 and 3 positions....	Thiazole Thiazole Thiazole, or 1,3-thiazole, is a clear to pale yellow flammable liquid with a pyridine-like odor and the molecular formula C3H3NS.... , Isothiazole Isothiazole An isothiazole is a type of organic compound containing a five-membered aromatic ring that consists of three carbon atoms, one nitrogen atom, and one sulfur atom....
Oxygen	Dioxolane Dioxolane Dioxolane or 1,3-dioxolane is an Heterocyclic compound acetal with the chemical formula C3H6O2. It is an analogue of tetrahydrofuran with an additional ring oxygen atom and an analogue of the 6 membered ring dioxane....
Sulfur	Dithiolane Dithiolane A dithiolane is a sulfur heterocyclic compound derived from cyclopentane by replacing two methylene groups with thioether groups. The parent compounds are 1,2-dithiolane and 1,3-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		1,2,3-Triazole 1,2,3-Triazole 1,2,3-Triazole is one of a pair of isomeric chemical compounds with molecular formula C2H3N3, called triazoles, which have a five-membered ring of two carbon atoms and three nitrogen atoms.... , 1,2,4-Triazole 1,2,4-Triazole 1,2,4-Triazole is one of a pair of isomeric chemical compounds with molecular formula C2H3N3, called triazoles, which have a five-membered ring of two carbon atoms and three nitrogen atoms....
Nitrogen/2-sulfur		Dithiazole

Five-member ring compounds with four heteroatoms:

Heteroatom	Saturated	Unsaturated
Nitrogen		Tetrazole Tetrazole Tetrazoles are a class of chemical synthesis organic heterocyclic compound organic compound, consisting of a 5-member ring of four nitrogen and one carbon atom ....

With 5-heteroatoms, the compound may be considered inorganic rather than heterocyclic. Pentazole

Pentazole

Pentazole is an aromatic compound consisting of a five-membered ring with all nitrogen atoms, one of which is bonded to a hydrogen atom. It has a molecular formula of HN5....
is the all nitrogen heteroatom unsaturated compound.

6-Membered rings

Six membered rings with a single heteroatom:

Heteroatom	Saturated	Unsaturated
Nitrogen	Piperidine Piperidine Piperidine is an organic compound with the molecular formula 5NH. This heterocyclic compound amine consists of a six-membered ring containing five methylene units and one nitrogen atom....	Pyridine Pyridine Pyridine is a simple and important heterocyclic aromatic organic compound with the formula CarbonHydrogenNitrogen. This colorless liquid with a distinctive fish-like odor is structurally related to benzene, wherein one CH group in the six-membered ring is replaced by a nitrogen atom....
Oxygen	Tetrahydropyran Tetrahydropyran Tetrahydropyran, or oxane, is the organic compound consisting of a saturated six-membered ring containing five carbon atoms and one oxygen atom....	Pyran Pyran In chemistry, a pyran is a six membered heterocyclic ring consisting of five carbon atoms and one oxygen atom and containing two double bonds. The molecular formula is C5H6O....
Sulfur	Thiane	Thiine (thiapyrane)

With two heteroatoms:

Heteroatom	Saturated	Unsaturated
Nitrogen	Piperazine Piperazine Piperazine is an organic compound that consists of a six-membered ring containing two opposing nitrogen atoms. Piperazine exists as small alkaline deliquescent crystals with a salt taste....	Diazine Diazine Diazine refers to a group of organic compounds having the molecular formula C4H4N2. Each contains a benzene ring in which two of the C-H fragments have been replaced by isolobal nitrogen.... s
Nitrogen / oxygen	Oxazine
Nitrogen / sulfur		Thiazine Thiazine Thiazines are organic compounds containing a ring of four carbon, one nitrogen and one sulfur atom. Chemicals that include thiazine are used for dyes, tranquilizers and insecticides....
Sulfur	Dithiane Dithiane A dithiane is a heterocyclic compound composed of a cyclohexane core structure with two methylene units replaced by sulfur. The parent compounds are 1,2-dithiane, 1,3-dithiane and 1,4-dithiane....
Oxygen	Dioxane	Dioxin

With three heteroatoms:

Heteroatom	Saturated	Unsaturated
Nitrogen		Triazine Triazine A triazine is one of three organic chemicals, isomeric with each other, whose empirical formula is 333....
Oxygen	Trioxane Trioxane Trioxane refers to a pair of isomeric organic compounds having the molecular formula C3H6O3. Each contains a six membered ring with three carbon atoms and three oxygen atoms....

With four heteroatoms:

Heteroatom	Saturated	Unsaturated
Nitrogen		Tetrazine Tetrazine Tetrazine is an unstable Chemical compound that consists of a six-membered aromatic ring containing four nitrogen atoms with the molecular formula Carbon2Hydrogen2Nitrogen4....

The hypothetical compound with six nitrogen heteroatoms would be hexazine

Hexazine

Hexazine is a hypothetical allotrope of nitrogen composed of 6 nitrogen atoms arranged in a ring-like structure analogous to that of benzene. It would be the final member of the azabenzene series, having all of the methylidyne groups of the benzene molecule replaced with nitrogen atoms....
.

7-Membered rings

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

Heteroatom	Saturated	Unsaturated
Nitrogen		Azepine
Sulfur		Thiepin Thiepin In organic chemistry, thiepine is an Saturation seven-membered heterocyclic compound, with six carbon atoms and one sulfur atom.Benzothiepines have one fused benzene group and dibenzothiepines such as dosulepin hydrochloride and zotepine have two fused benzene groups....

Those with two heteroatoms include:

Heteroatom	Saturated	Unsaturated
Nitrogen		Diazepine Diazepine Diazepine is a seven-membered heterocyclic compound with two nitrogen atoms and three double bonds.When combined with a benzene ring, it is the basis of the benzodiazepine family of compounds....

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

Indole

Indole is an aromatic Heterocyclic compound organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring....
or isoindole

Isoindole

Isoindole in heterocyclic chemistry is a arene compound fused pyrrole. The compound is an isomer of indole and its organic reduction form is an isoindoline....
depending on the orientation. The pyridine analog is quinoline

Quinoline

Quinoline, also known as 1-azanaphthalene, 1-benzazine, or benzo[b]pyridine, is a heterocyclic aromatic organic compound. It has the formula C9H7N and is a colourless hygroscopic liquid with a strong odour....
or isoquinoline

Isoquinoline

Isoquinoline, also known as benzo[c]pyridine or 2-benzanine, is a heterocyclic aromatic organic compound. It is a structural isomer of quinoline....
. For azepine, benzazepine

Benzazepines

Benzazepines are heterocyclic compounds consisting of a benzene ring fused to an azepine ring. Examples include fenoldopam, and galantamine....
is the preferred name. Similarly, the compounds with two benzene rings fused to the central heterocycle are carbazole

Carbazole

Carbazole is an aromatic Heterocyclic compound organic compound. It has a tricyclic structure, consisting of two six-membered benzene ring fused on either side of a five-membered nitrogen-containing ring....
, acridine

Acridine

Acridine, C13H9N, is an organic compound and a heterocyclic compound. Acridine is also used to describe compounds containing the C13N tricycle....
, and dibenzoazepine.

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