Editing Heterocyclic compound

{{short description|Molecule with one or more rings composed of different elements}}
{{Other uses of|ring structure|Ring structure (disambiguation){{!}}Ring structure}}
{{for|the journal|Heterocycles (journal)}}
{{Use dmy dates|date=July 2022}}

[[File:Heterocycle compounds.jpg|thumb|right|class=skin-invert|280px|Structures and names of common heterocyclic compounds]]
[[Image:Pyridine.svg|thumb|class=skin-invert|right|125px|[[Pyridine]], a heterocyclic compound]]

A '''heterocyclic compound''' or '''ring structure''' is a [[cyclic compound]] that has atoms of at least two different [[chemical element|elements]] as members of its ring(s).<ref>[[IUPAC Gold Book]] [http://goldbook.iupac.org/H02798.html ''heterocyclic compounds'']</ref> '''Heterocyclic organic chemistry''' is the branch of [[organic chemistry]] dealing with the synthesis, properties, and applications of '''organic heterocycles'''.<ref name=Gilchrist/>

Examples of heterocyclic compounds include all of the [[nucleic acids]], the majority of drugs, most [[biomass]] ([[cellulose]] and related materials), and many natural and synthetic dyes.  More than half of known compounds are heterocycles.<ref name=Rees>{{cite journal |doi=10.1002/jhet.5570290306|title=Polysulfur-Nitrogen Heterocyclic Chemistry|year=1992|last1=Rees|first1=Charles W.|journal=Journal of Heterocyclic Chemistry|volume=29|issue=3|pages=639–651}}</ref>  59% of US [[FDA]]-approved drugs contain [[nitrogen]] heterocycles.<ref>{{cite journal|author=Edon Vitaku, David T. Smith, Jon T. Njardarson|title=Analysis of the Structural Diversity, Substitution Patterns, and Frequency of Nitrogen Heterocycles among U.S. FDA Approved Pharmaceuticals|journal=J. Med. Chem.|volume=57|year=2014|issue=24|pages=10257–10274|doi=10.1021/jm501100b|pmid=25255204}}</ref>

== Classification ==
The study of organic heterocyclic chemistry focuses especially on organic unsaturated derivatives, and the preponderance of work and applications involves unstrained organic 5- and 6-membered rings.  Included are [[pyridine]], [[thiophene]], [[pyrrole]], and [[furan]].  Another large class of organic heterocycles refers to those fused to [[benzene ring]]s. For example, the fused benzene derivatives of pyridine, thiophene, pyrrole, and furan are [[quinoline]], [[benzothiophene]], [[indole]], and [[benzofuran]], respectively.  The fusion of two benzene rings gives rise to a third large family of organic compounds. Analogs of the previously mentioned heterocycles for this third family of compounds are [[acridine]], [[dibenzothiophene]], [[carbazole]], and [[dibenzofuran]], respectively.  

Heterocyclic organic compounds can be usefully classified based on their electronic structure. The saturated organic heterocycles behave like the acyclic derivatives. Thus, [[piperidine]] and [[tetrahydrofuran]] are conventional [[amines]] and [[ethers]], with modified steric profiles. Therefore, the study of organic heterocyclic chemistry focuses on organic unsaturated rings.

===Inorganic rings===
Some heterocycles contain no carbon. Examples are [[borazine]] (B<sub>3</sub>N<sub>3</sub> ring), [[phosphazene]] (P<sub>3</sub>N<sub>3</sub> ring), and [[tetrasulfur tetranitride]] (S<sub>4</sub>N<sub>4</sub> ring). In comparison with organic heterocycles, which have numerous commercial applications, inorganic ring systems are mainly of theoretical interest. [[International Union of Pure and Applied Chemistry|IUPAC]] recommends the [[Hantzsch-Widman nomenclature]] for naming heterocyclic compounds.<ref>{{GoldBookRef|title=Hantzsch–Widman name|file=H02737}}</ref>

==Notes on lists==
* "Heteroatoms" are atoms in the ring other than [[carbon]] atoms.
* Names in italics are retained by [[IUPAC]] and do not follow the [[Hantzsch-Widman nomenclature]]
* Some of the names refer to classes of compounds rather than individual compounds.
* Also no attempt is made to list [[isomers]].

== 3-membered rings ==
Although subject to [[ring strain]], 3-membered heterocyclic rings are well characterized.<ref>{{March6th}}</ref>

{| class="wikitable"
|-
! colspan="3" | Three-membered rings with one heteroatom
|-
! Heteroatom
! Saturated
! Unsaturated
|-
| Boron
| [[Borirane]]
| [[Borirene]]
|-
| Nitrogen
| [[Aziridine]]
| [[Azirine]]
|-
| Oxygen
| [[Oxirane]]<br>([[ethylene oxide]], [[epoxide]]s)
| [[Oxirene]]
|-
| Phosphorus
| [[Phosphirane]]
| [[Phosphirene]]
|-
| Sulfur
| [[Thiirane]]<br>([[ethylene sulfide]], [[episulfide]]s)
| [[Thiirene]]
|-
! colspan="3" | Three-membered rings with two heteroatoms
|-
! Heteroatoms
! Saturated
! Unsaturated
|-
| 2 × Nitrogen
| [[Diaziridine]]
| [[Diazirine]]
|-
| Nitrogen + Oxygen
| [[Oxaziridine]]
| [[Oxazirine]]
|-
| Nitrogen + Sulfur
| [[Thiaziridine]]
| [[Thiazirine]]
|-
| 2 × Oxygen
| [[Dioxirane]] (highly unstable)
|
|-
| 2 × Sulfur
| [[Dithiirane]] (highly unstable)
|
|}

== 4-membered rings ==
{| class="wikitable"
|-
! colspan="3" | Four-membered rings with one heteroatom
|-
! Heteroatom
! Saturated
! Unsaturated
|-
| Boron
| [[Boretane]]
| [[Borete]]
|-
| Nitrogen
| [[Azetidine]]
| [[Azete]]
|-
| Oxygen
| [[Oxetane]]
| [[Oxete]]
|-
| Phosphorus
| [[Phosphetane]]
| [[Phosphete]]
|-
| Sulfur
| [[Thietane]]
| [[Thiete]]
|-
! colspan="3" | Four-membered rings with two heteroatoms
|-
! Heteroatoms
! Saturated
! Unsaturated
|-
| 2 × Nitrogen
| [[Diazetidine]]
| [[Diazete]]
|-
| 2 × Oxygen
| [[Dioxetane]]
| [[Dioxete]]
|-
| 2 × Sulfur
| [[Dithietane]]
| [[Dithiete]]
|}

== 5-membered rings ==
The 5-membered ring compounds containing ''two'' heteroatoms, at least one of which is nitrogen, are collectively called the [[azole]]s. [[Thiazole]]s and [[isothiazole]]s contain a sulfur and a nitrogen atom in the ring. [[Dithiole]]s have two sulfur atoms.

A large group of 5-membered ring compounds with ''three'' or more heteroatoms also exists. One example is the class of [[dithiazole]]s, which contain two sulfur atoms and one nitrogen atom.

{| class="wikitable"
|-
! colspan="3" | Five-membered rings with one heteroatom
|-
! Heteroatom
! Saturated
! Unsaturated
|-
| [[Antimony]]
| [[Stibolane]]
| [[Stibole]]
|-
| [[Arsenic]]
| [[Arsolane]]
| [[Arsole]]
|-
| [[Bismuth]]
| [[Bismolane]]
| [[Bismole]]
|-
| [[Boron]]
| [[Borolane]]
| [[Borole]]
|-
| [[Germanium]]
| [[Germolane]]
| [[Germole]]
|-
| [[Nitrogen]]
| ''[[Pyrrolidine]]''<br>([[Azolidine]] not used)
| ''[[Pyrrole]]''<br>([[Azole]] not used)<br>''[[Pyrroline]]'' (partially unsaturated)
|-
| [[Oxygen]]
| [[Oxolane]]
| ''[[Furan]]''<br>([[Oxole]] not used)
|-
| [[Phosphorus]]
| [[Phospholane]]
| [[Phosphole]]
|-
| [[Selenium]]
| [[Selenolane]]
| [[Selenophene]]
|-
| [[Silicon]]
| [[Silolane]]
| [[Silole]]
|-
| [[Sulfur]]
| [[Thiolane]]
| ''[[Thiophene]]''<br>([[Thiole]] not used)
|-
| [[Tellurium]]
| [[Tellurolane]]
| [[Tellurophene]]
|-
| [[Tin]]
| [[Stannolane]]
| [[Stannole]]
|-
! colspan="3" | Five-membered rings with two heteroatoms
|-
! Heteroatoms
! Saturated
! Unsaturated (and partially unsaturated)
|-
| 2 × Nitrogen
| ''[[Pyrazolidine]]'' <br>''[[Imidazolidine]]''
| ''[[Pyrazole]]'' (''[[Pyrazoline]]'')<br>''[[Imidazole]]'' (''[[Imidazoline]]'')
|-
| Nitrogen + Oxygen
| [[Oxazolidine]]<br>[[Isoxazolidine]]
| [[Oxazole]] ([[Oxazoline]])<br>[[Isoxazole]] ([[Isoxazoline]])
|-
| Nitrogen + Sulfur
| [[Thiazolidine]]<br>[[Isothiazolidine]]
| [[Thiazole]] ([[Thiazoline]])<br>[[Isothiazole]] ([[Isothiazoline]])
|-
| Oxygen + Sulfur
| [[Oxathiolane]]<br>[[Isoxathiolane]]
| [[Oxathiole]]<br>[[Isoxathiole]]
|-
| 2 × Oxygen
| [[Dioxolane]]
| [[Dioxole]]
|-
| 2 × Sulfur
| [[Dithiolane]]
| [[Dithiole]]
|-
! colspan="3" | Five-membered rings with three heteroatoms
|-
! Heteroatoms
! Saturated
! Unsaturated
|-
| 3 × Nitrogen
|
| [[Triazole]]
|-
| 2 Nitrogen + Oxygen
|
| [[Oxadiazole]]
|-
| 2 Nitrogen + Sulfur
|
| [[Thiadiazole]]
|-
| Nitrogen + 2 Oxygen
|
| [[Dioxazole]]
|-
| Nitrogen + 2 Sulfur
|
| [[Dithiazole]]
|-
! colspan="3" | Five-membered rings with four heteroatoms
|-
! Heteroatoms
! Saturated
! Unsaturated
|-
| 4 × Nitrogen
|
| [[Tetrazole]]
|-
| 3 Nitrogen + Oxygen
|
| [[Oxatriazole]]
|-
| 3 Nitrogen + Sulfur
|
| [[Thiatriazole]]
|-
! colspan="3" | Five-membered rings with five heteroatoms
|-
! Heteroatoms
! Saturated
! Unsaturated
|-
| 5 × Nitrogen
|
| [[Pentazole]]
|-
| 4 Nitrogen + Oxygen
|
| [[Oxatetrazole]]
|-
| 4 Nitrogen + Sulfur
|
| [[Thiatetrazole]]
|}

== 6-membered rings ==
The 6-membered ring compounds containing ''two'' heteroatoms, at least one of which is nitrogen, are collectively called the [[Azine (heterocycle)|azines]]. [[Thiazine]]s contain a sulfur and a nitrogen atom in the ring. [[Dithiin]]es have two sulfur atoms.

{| class="wikitable"
|-
! colspan="4" | Six-membered rings with one heteroatom
|-
! Heteroatom
! Saturated
! Unsaturated
! Ions
|-
| [[Antimony]]
| [[Stibinane]]
| [[Stibinine]]
| [[Stibatabenzene]] cation
|-
| [[Arsenic]]
| [[Arsinane]]
| [[Arsinine]]
| [[Arsatabenzene]] cation
|-
| [[Bismuth]]
| [[Bisminane]]
| [[Bismine]]
| [[Bismatabenzene]] cation
|-
| [[Boron]]
| [[Borinane]]
| [[Borinine]]
| [[Boratabenzene]] anion
|-
| [[Germanium]]
| [[Germinane]]
| [[Germine]]
|
|-
| [[Nitrogen]]
| ''[[Piperidine]]''<br>([[Azinane]] not used)
| ''[[Pyridine]]''<br>([[Azine (heterocycle)|Azine]] not used)
| [[Pyridinium]] cation
|-
| [[Oxygen]]
| [[Oxane]]
| ''[[Pyran]]''<br>([[Oxine]] not used)
| [[Pyrylium]] cation
|-
| [[Phosphorus]]
| [[Phosphinane]]
| [[Phosphinine]]
| [[Phosphininium]] cation<ref name="C5R5PH+">{{cite journal |last1=Fischer |first1=Lukas |last2=Wossidlo |first2=Friedrich |last3=Frost |first3=Daniel |last4=Coles |first4=Nathan T. |last5=Steinhauer |first5=Simon |last6=Riedel |first6=Sebastian |last7=Müller |first7=Christian |date=6 August 2021 |orig-date=19th July 2021 |title=One-step methylation of aromatic phosphorus heterocycles: synthesis and crystallographic characterization of a 1-methyl-phosphininium salt |url=https://pubs.rsc.org/en/content/articlehtml/2021/cc/d1cc03892c |journal=Chemical Communications |volume= |issue=2021, '''57''' |publisher= Royal Society of Chemistry |pages=9522-9525 |doi=10.1039/D1CC03892C  |access-date=7 March 2025 }}</ref>
|-
| [[Selenium]]
| [[Selenane]]
| [[Selenopyran]]
| [[Selenopyrylium]] cation
|-
| [[Silicon]]
| [[Silinane]]
| [[Siline]]
|
|-
| [[Sulfur]]
| [[Thiane]]
| ''[[Thiopyran]]''<br>([[Thiine]] not used)
| [[Thiopyrylium]] cation
|-
| [[Tellurium]]
| [[Tellurane]]
| [[Telluropyran]]
| [[Telluropyrylium]] cation
|-
| [[Tin]]
| [[Stanninane]]
| [[Stannine]]
|
|-
! colspan="3" | Six-membered rings with two heteroatoms
|-
! Heteroatoms
! Saturated
! Unsaturated
|-
| 2 × Nitrogen
| ''[[Piperazine]]''
| ''[[Pyrazine]]''<br>''[[Pyrimidine]]''<br>''[[Pyridazine]]''
|-
| Nitrogen + Oxygen
| ''[[Morpholine]]''
| [[Oxazine]]
|-
| Nitrogen + Sulfur
| ''[[Thiomorpholine]]''
| [[Thiazine]]
|-
| Oxygen + Sulfur
| [[Oxathiane]]
| [[Oxathiin]]
|-
| 2 × Oxygen
| [[Dioxane]]
| [[Dioxin]]
|-
| 2 × Sulfur
| [[Dithiane]]
| [[Dithiin]]
|-
! colspan="3" | Six-membered rings with three heteroatoms
|-
! Heteroatoms
! Saturated
! Unsaturated
|-
| 3 × Nitrogen
| [[Triazinane]]
| [[Triazine]]
|-
| 3 × Oxygen
| [[Trioxane]]
| [[Trioxin]]
|-
| 3 × Sulfur
| [[Trithiane]]
| [[Trithiin]]
|-
! colspan="3" | Six-membered rings with four heteroatoms
|-
! Heteroatoms
! Saturated
! Unsaturated
|-
| 4 × Nitrogen
|
| [[Tetrazine]]
|-
| 2 Nitrogen + 2 Boron
|
| [[Carborazine]]
|}

'''Six-membered rings with five heteroatoms'''<br>The [[hypothetical chemical compound]] with five nitrogen heteroatoms would be [[pentazine]].

'''Six-membered rings with six heteroatoms'''<br>The [[hypothetical chemical compound]] with six nitrogen heteroatoms would be [[hexazine]]. [[Borazine]] is a six-membered ring with three nitrogen heteroatoms and three boron heteroatoms.

== 7-membered rings ==
In a 7-membered ring, the heteroatom must be able to provide an empty π-orbital (e.g. boron) for "normal" aromatic stabilization to be available; otherwise, [[homoaromaticity]] may be possible.

{| class="wikitable"
|-
! colspan="3" | Seven-membered rings with one heteroatom
|-
! Heteroatom
! Saturated
! Unsaturated
|-
| Boron
| [[Borepane]]
| [[Borepine]]
|-
| Nitrogen
| [[Azepane]]
| [[Azepine]]
|-
| Oxygen
| [[Oxepane]]
| [[Oxepine]]
|-
| Phosphorus
| [[Phosphepane]]
| [[Phosphepine]]
|-
| Sulfur
| [[Thiepane]]
| [[Thiepine]]
|-
! colspan="3" | Seven-membered rings with two heteroatoms
|-
! Heteroatoms
! Saturated
! Unsaturated
|-
| 2 × Nitrogen
| [[Diazepane]]
| [[Diazepine]]
|-
| Nitrogen + Oxygen
| [[Oxazepane]]
| [[Oxazepine]]
|-
| Nitrogen + Sulfur
| [[Thiazepane]]
| [[Thiazepine]]
|}

== 8-membered rings ==
{| class="wikitable"
|-
! Heteroatom
! Saturated
! Unsaturated
|-
| Nitrogen
| [[Azocane]]
| [[Azocine]]
|-
| Oxygen
| [[Oxocane]]
| [[Oxocine]]
|-
| Sulfur
| [[Thiocane]]
| [[Thiocine]]
|}

[[Borazocine]] is an eight-membered ring with four nitrogen heteroatoms and four boron heteroatoms.

== 9-membered rings ==
{| class="wikitable"
|-
! Heteroatom
! Saturated
! Unsaturated
|-
| Nitrogen
| [[Azonane]]
| [[Azonine]]
|-
| Oxygen
| [[Oxonane]]
| [[Oxonine]]
|-
| Sulfur
| [[Thionane]]
| [[(2Z,4Z,6Z,8Z)-Thionine|Thionine]]
|}

== Images of rings with one heteroatom ==
{| class="wikitable"
|-
!  colspan="1" | || colspan="3" | Saturated || colspan="3" | Unsaturated
|-
! Heteroatom !! [[Nitrogen]] !! [[Oxygen]] !! [[Sulfur]] !! Nitrogen !! Oxygen !! Sulfur
|-
!  rowspan="2" | 3-atom ring
| [[Aziridine]] || [[Oxirane]] || [[Thiirane]] || [[Azirine]] || [[Oxirene]] || [[Thiirene]]
|-
| [[File:Aziridin.svg|60px|Structure of aziridine]] || [[File:Ethylene oxide.svg|60px|Structure of oxirane]] || [[File:Thiiran.svg|60px|Structure of thiirane]] || [[File:Azirin.svg|60px|Structure of azirine]] || [[File:Oxiren.svg|60px|Structure of oxirene]] || [[File:Thiiren.svg|60px|Structure of thiirene]]
|-
!  rowspan="2" | 4-atom ring
| [[Azetidine]] || [[Oxetane]] || [[Thietane]] || [[Azete]] || [[Oxete]] || [[Thiete]]
|-
| [[File:Azetidine structure.svg|70px|Structure of acetidine]] || [[File:Oxetan.png|60px|Structure of oxetane]] || [[File:Thietan.png|60px|Structure of thietane]] || [[File:Azete structure.svg|60px|Structure of azete]] || [[File:Oxetene.svg|70px|Structure of oxete]] || [[File:Thietene.png|70px|Structure of thiete]]
|-
!  rowspan="2" | 5-atom ring
| ''[[Pyrrolidine]]'' || [[Oxolane]] || [[Thiolane]] || ''[[Pyrrole]]'' || ''[[Furan]]'' || ''[[Thiophene]]''
|-
| [[File:Pyrrolidine-Structural Formula V.1.svg|60px|Structure of pyrrolidine]] || [[File:Tetrahydrofuran acsv.svg|70px|Structure of oxolane]] || [[File:Tetrahydrothiophen.png|70px|Structure of thiolane]] || [[File:Pyrrol2.svg|70px|Structure of pyrrole]] || [[File:Furan.svg|70px|Structure of furan]] || [[File:Thiophen.svg|70px|Structure of thiophene]]
|-
!  rowspan="2" | 6-atom ring
| ''[[Piperidine]]'' || [[Oxane]] || [[Thiane]] || ''[[Pyridine]]'' || ''[[Pyran]]'' || ''[[Thiopyran]]''
|-
| [[File:Piperidin.svg|70px|Structure of piperidine]] || [[File:Tetrahydropyran (vzorec).svg|70px|Structure of oxane]] || [[File:Thiane3.svg|70px|Structure of thiane]] || [[File:Pyridin.svg|70px|Structure of pyridine]] || [[File:Pyran.svg|70px|Structure of pyran]] || [[File:1,2-Thiapyran.svg|70px|Structure of thiopyran]]
|-
!  rowspan="2" | 7-atom ring
| [[Azepane]] || [[Oxepane]] || [[Thiepane]] || [[Azepine]] || [[Oxepine]] || [[Thiepine]]
|-
| [[File:Azepane.svg|70px|Structure of azepane]] || [[File:Oxepan.png|70px|Structure of oxepane]] || [[File:Thiepan.svg|70px|Structure of thiepane]] || [[File:Azepine-2D-skeletal.png|70px|Structure of azepine]] || [[File:Oxepine.svg|70px|Structure of oxepine]] || [[File:Thiepine.png|70px|Structure of thiepine]]
|-
!  rowspan="2" | 8-atom ring
| [[Azocane]] || [[Oxocane]] || [[Thiocane]] || [[Azocine]] || [[Oxocine]] || [[Thiocine]]
|-
| [[File:Azocane.png|70px|Structure of azocane]] || [[File:Oxocano.png|70px|Structure of oxocane]] || [[File:Tiocano.png|70px|Structure of thiocane]] || [[File:Azocine.png|70px|Structure of azocine]] || [[File:Oxocinio.png|70px|Structure of oxocine]] || [[File:Tiocinio.png|70px|Structure of thiocine]]
|-
!  rowspan="2" | 9-atom ring
| [[Azonane]] || [[Oxonane]] || [[Thionane]] || [[Azonine]] || [[Oxonine]] || [[(2Z,4Z,6Z,8Z)-Thionine|Thionine]]
|-
| [[File:Azonano.png|70px|Structure of azonane]] || [[File:Oxonano.png|70px|Structure of oxonane]] || [[File:Tionano.png|70px|Structure of thionane]] || [[File:Azonina.png|70px|Structure of azonine]] || [[File:Oxonina.png|70px|Structure of oxonine]] || [[File:Tionina.png|70px|Structure of thionine]]
|}

== Fused/condensed rings ==
Heterocyclic rings systems that are formally derived by fusion with other rings, either [[Carbocycle|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 derivative is [[quinoline]] or [[isoquinoline]], and the class of analogues with two nitrogen atoms is known as the [[benzodiazine]]s. For the azepine derivative, [[benzazepine]] is the preferred name. Likewise, the compounds with two benzene rings fused to the central heterocycle are [[carbazole]], [[acridine]], and [[dibenzoazepine]]. [[Heptazine]] is a tricyclic nitrogen-containing heterocyclic system derived by fusion of three triazine rings, and analog of the carbocycle [[phenalene]].

== History of heterocyclic chemistry ==
The history of heterocyclic chemistry began in the 1800s, in step with the development of [[organic chemistry]].  Some noteworthy developments:<ref>{{Cite journal |doi=10.1021/ed063p860|title=Adrien Albert and the rationalization of heterocyclic chemistry|journal=Journal of Chemical Education|volume=63|issue=10|pages=860|year=1986|last1=Campaigne|first1=E.|bibcode=1986JChEd..63..860C}}</ref>
* 1818: Brugnatelli makes [[alloxan]] from [[uric acid]]
* 1832: Dobereiner produces [[furfural]] (a furan) by treating [[starch]] with [[sulfuric acid]]
* 1834: Runge obtains [[pyrrole]] ("fiery oil") by dry distillation of bones
* 1906: Friedlander synthesizes [[indigo dye]], allowing synthetic chemistry to displace a large agricultural industry
* 1936: [[Alfred E. Treibs|Treibs]] isolates chlorophyll derivatives from crude oil, explaining the biological origin of petroleum.
* 1951: [[Chargaff's rules]] are described, highlighting the role of heterocyclic compounds ([[purine]]s and [[pyrimidine]]s) in the genetic code.

== Uses ==
Heterocyclic compounds are pervasive in many areas of life sciences and technology.<ref name=Gilchrist>Thomas L. Gilchrist "Heterocyclic Chemistry" 3rd ed. Addison Wesley: Essex, England,
1997. 414 pp. {{ISBN|0-582-27843-0}}.</ref>  Many drugs are heterocyclic compounds.<ref>{{Cite web|url=http://www.ipexl.com/share/f593e64bc3679cb669d02c007efdca17|title=IPEXL.com Multilingual Patent Search, Patent Ranking|website=www.ipexl.com|access-date=8 September 2010|archive-date=24 September 2015|archive-url=https://web.archive.org/web/20150924035914/http://www.ipexl.com/share/f593e64bc3679cb669d02c007efdca17|url-status=dead}}</ref>
==See also==
*[[Spiroketals]]

== References ==
{{reflist}}

== External links ==
{{commons category|Heterocyclic compounds|lcfirst=yes}}
{{wikiquote}}
* [http://www.chem.qmul.ac.uk/iupac/hetero/HW.html Hantzsch-Widman nomenclature, IUPAC]
* [http://www.cancer.gov/cancertopics/factsheet/Risk/heterocyclic-amines Heterocyclic amines in cooked meat, US CDC]
* [http://www.cancer.org/docroot/PED/content/PED_1_3x_Known_and_Probable_Carcinogens.asp List of known and probable carcinogens, American Cancer Society] {{Webarchive|url=https://web.archive.org/web/20031213030702/http://www.cancer.org/docroot/PED/content/PED_1_3x_Known_and_Probable_Carcinogens.asp |date=13 December 2003 }}
* [http://www.scorecard.org/chemical-groups/one-list.tcl?short_list_name=p65 List of known carcinogens by the State of California], [[Proposition 65]] (more comprehensive)

{{Authority control}}

{{DEFAULTSORT:Heterocyclic Compound}}
[[Category:Heterocyclic compounds| ]]