View source for Hantzsch–Widman nomenclature

'''Hantzsch–Widman nomenclature''', also called the '''extended Hantzsch–Widman system''', is a type of [[Systematic name|systematic]] [[IUPAC nomenclature of organic chemistry|chemical nomenclature]] used for naming [[heterocycle]]s (cyclic [[chemical compound]]s which contain both carbon atoms and atoms of other elements in the ring).<ref>{{GoldBookRef|title=Hantzsch–Widman name|file=H02737|accessdate=2009-11-22}}</ref> It is used for rings which contain at least one carbon atom and ten atoms or fewer in total in the ring, although some common heterocyclic compounds have [[retained name]]s which do no follow the Hantzsch–Widman pattern.<ref name="IUPAC83">{{IUPAC Hanzsch-Widman 1982}}.</ref><ref name="IUPAC93">{{BlueBook1993|pages=40–44|rec=2.3.3|url=http://www.acdlabs.com/iupac/nomenclature/93/r93_209.htm}}</ref>

Hantzsch–Widman nomenclature is named after the German chemists [[Arthur Rudolf Hantzsch|Arthur Hantzsch]] and [[Oskar Widman]], who independently proposed similar methods for the systematic naming of heterocyclic compounds in 1887 and 1888 respectively.<ref>{{citation | last1 = Hantzsch | first1 = A. | authorlink1 = Arthur Rudolf Hantzsch | last2 = Weber | first2 = J. H. | year = 1887 | title = Ueber Verbindungen des Thiazols (Pyridins der Thiophenreihe) | journal = Ber. Dtsch. Chem. Ges. | volume = 20 | pages = 3118–32 | doi = 10.1002/cber.188702002200}}.</ref><ref>{{citation | last = Widman | first = O. | year = 1888 | title = Zur Nomenclatur der Verbindungen, welche Stickstoffkerne enthalten | journal = J. Prakt. Chem. | volume = 38 | pages = 185–201 | doi = 10.1002/prac.18880380114}}.</ref> It forms the basis for many common chemical names, such as [[dioxin (chemical)|dioxin]] and [[benzodiazepine]].

A Hantzsch–Widman name will always contain a prefix, which indicates the type of heteroatom present in the ring, and a stem, which indicates both the total number of atoms and the presence or absence of [[double bond]]s. The name may include more than one prefix, if more than one type of heteroatom is present; a multiplicative prefix is there are several heteroatoms of the same type; and locants to indicate the relative positions of the different atoms. Hantzsch–Widman names may be combined with other aspects of organic nomenclature, to indicate substitution or fused-ring systems.

==Prefixes==
{| class="wikitable" align=right style="margin:0 0 0 0.5em;"
|-
! Element !! Prefix !! rowspan=11|&nbsp; !! Element !! Prefix
|-
| [[Fluorine]] || fluora || [[Arsenic]] || arsa
|-
| [[Chlorine]] || chlora || [[Antimony]] || stiba
|-
| [[Bromine]] || broma || [[Bismuth]] || bisma
|-
| [[Iodine]] || ioda || [[Silicon]] || sila
|-
| [[Oxygen]] || oxa || [[Germanium]] || germana
|-
| [[Sulfur]] || thia || [[Tin]] || stanna
|-
| [[Selenium]] || selena || [[Lead]] || plumba
|-
| [[Tellurium]] || tellura || [[Boron]] || bora
|-
| [[Nitrogen]] || aza || [[Mercury]] || mercura
|-
| [[Phosphorus]] || phospha || colspan=2 | &nbsp;
|-
|}

The Hantzsch–Widman prefixes indicate the type of heteroatom(s) present in the ring. They form a priority series: if there is more than one type of heteroatom in the ring, the prefix which is higher on the list comes before the prefix which is lower on the list. For example, "oxa" (for [[oxygen]]) always comes before "aza" (for [[nitrogen]]) in a name. The priority order is the same as that used in [[replacement nomenclature]], but Hantzsch–Widman nomenclature is only recommended for use with a more restricted set of heteroatoms (see also below).<ref name="IUPAC93" /><ref group=note>The 2004 Draft Recommendations propose adding [[aluminium]] (aluma), [[gallium]] (galla), [[indium]] (indiga) and [[thallium]] (thalla) to the list of heteroatoms for which Hantzsch–Widman nomenclature is used, and removing [[mercury]].</ref>

All of the prefixes end in "a": in Hantzsch–Widman nomenclature (but not in some other methods of naming heterocycles), the final "a" is [[Elision|elided]] when the prefix comes before a vowel.

The heteroatom is assumed to have its standard [[bonding number]] for organic chemistry while the name is being constructed. The [[halogen]]s have a standard bonding number of one, and so a heterocyclic ring containing a halogen as a heteroatom should have a formal positive charge.<ref>{{IUPAC radicals 1993}}.</ref> In principle, [[lambda nomenclature]] could be used to specify a non-standard [[Valence (chemistry)|valence state]] for a heteroatom<ref name="IUPAC93" /> but, in practice, this is rare.

==Stems==
The choice of stem is quite complicated, and not completely standardised. The main criteria are:
*the total number of atoms in the ring, both carbon atoms and heteroatoms ("ring size");
*the presence of any [[double bond]]s;
*the nature of the heteroatoms.

{| class="wikitable"
|-
|+ Three- to five-membered rings
|-
! rowspan=2 | Ring size
! colspan=2 | Unsaturated
! colspan=2 | Saturated
|-
| align=center | containing<br/>nitrogen
| align=center | not containing<br/>nitrogen
| align=center | containing<br/>nitrogen
| align=center | not containing<br/>nitrogen
|-
| '''3'''
| align=center | -irene*
| align=center | -irene
| align=center | -iridine
| align=center | -irane
|-
| '''4'''
| align=center | -ete
| align=center | -ete
| align=center | -etidine
| align=center | -etane
|-
| '''5'''
| align=center | -ole
| align=center | -ole
| align=center | -olidine
| align=center | -olane
|-
|}
<nowiki>*</nowiki> Three-membered rings that only contain nitrogen can be named with the suffix -irine: hence [[azirine]] and [[diazirine]].

{| class="wikitable"
|-
|+ Six-membered rings
|-
! Heteroatom of<br/>''lowest'' priority
! Unsaturated
! Saturated
|-
| O, S, Se, Te, Bi, Hg
| align=center | -ine
| align=center | -ane
|-
| N, Si, Ge, Sn, Pb
| align=center | -ine
| align=center | -inane
|-
| B, F, Cl, Br, I, P, As, Sb
| align=center | -inine
| align=center | -inane
|-
|}

{| class="wikitable"
|-
|+ Seven- to ten-membered rings
|-
! Ring size
! Unsaturated
! Saturated
|-
| '''7'''
| -epine
| -epane
|-
| '''8'''
| -ocine
| -ocane
|-
| '''9'''
| -onine
| -onane
|-
| '''10'''
| -ecine
| -ecane
|-
|}

==Numbering==
If there is a single heteroatom, the [[Locant|numbering]] starts from the heteroatom. If there are two or more identical heteroatoms, the numbering starts at one of the heteroatoms and continues to give the loweest set of numbers. If there are two or more different heteroatoms, the numbering starts at the heteroatom of highest priority in the list of prefixes and continues to give the lowest set of numbers (without regard to the priority of the remaining heteroatoms).

==Indicated hydrogen==

==Notes==
{{reflist|group=note}}

==References==
{{reflist}}

[[Category:Chemical nomenclature]]
[[Category:Heterocyclic compounds|*]]

{{Imported from Wikipedia|name=Hantzsch–Widman nomenclature|id=327291410}}