Hantzsch–Widman nomenclature
Hantzsch–Widman nomenclature, also called the extended Hantzsch–Widman system, is a type of systematic chemical nomenclature used for naming heterocycles (cyclic chemical compounds which contain both carbon atoms and atoms of other elements in the ring).[1] 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 names which do no follow the Hantzsch–Widman pattern.[2][3]
Hantzsch–Widman nomenclature is named after the German chemists Arthur Hantzsch and Oskar Widman, who independently proposed similar methods for the systematic naming of heterocyclic compounds in 1887 and 1888 respectively.[4][5] It forms the basis for many common chemical names, such as 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 bonds. 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
| Element | Prefix | 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 | |||
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).[3][note 1]
All of the prefixes end in "a": in Hantzsch–Widman nomenclature (but not in some other methods of naming heterocycles), the final "a" is 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 halogens have a standard bonding number of one, and so a heterocyclic ring containing a halogen as a heteroatom should have a formal positive charge.[6] In principle, lambda nomenclature could be used to specify a non-standard valence state for a heteroatom[3] 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 bonds;
- the nature of the heteroatoms.
| Ring size | Unsaturated | Saturated | ||
|---|---|---|---|---|
| containing nitrogen |
not containing nitrogen |
containing nitrogen |
not containing nitrogen | |
| 3 | -irene* | -irene | -iridine | -irane |
| 4 | -ete | -ete | -etidine | -etane |
| 5 | -ole | -ole | -olidine | -olane |
* Three-membered rings that only contain nitrogen can be named with the suffix -irine: hence azirine and diazirine.
| Heteroatom of lowest priority |
Unsaturated | Saturated |
|---|---|---|
| O, S, Se, Te, Bi, Hg | -ine | -ane |
| N, Si, Ge, Sn, Pb | -ine | -inane |
| B, F, Cl, Br, I, P, As, Sb | -inine | -inane |
| Ring size | Unsaturated | Saturated |
|---|---|---|
| 7 | -epine | -epane |
| 8 | -ocine | -ocane |
| 9 | -onine | -onane |
| 10 | -ecine | -ecane |
Numbering
If there is a single heteroatom, the 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
References
- ↑ Hantzsch–Widman name, <http://goldbook.iupac.org/H02737.html> (accessed 22 November 2009), Compendium of Chemical Terminology Internet edition; International Union of Pure and Applied Chemistry (IUPAC)
- ↑ Revision of the Extended Hantzsch–Widman System of Nomenclature for Heteromonocycles (IUPAC Recommendations 1982). Pure Appl. Chem., 55 (2), 409–16. DOI: 10.1351/pac198855020409..
- ↑ 3.0 3.1 3.2 Rule R-2.3.3. In A Guide to IUPAC Nomenclature of Organic Compounds; IUPAC Recommendations 1993; Blackwell Science: Oxford, 1993; pp 40–44. ISBN 0-632-03488-2, <http://www.acdlabs.com/iupac/nomenclature/93/r93_209.htm>
- ↑ Hantzsch, A.; Weber, J. H. Ueber Verbindungen des Thiazols (Pyridins der Thiophenreihe). Ber. Dtsch. Chem. Ges. 1887, 20, 3118–32. DOI: 10.1002/cber.188702002200.
- ↑ Widman, O. Zur Nomenclatur der Verbindungen, welche Stickstoffkerne enthalten. J. Prakt. Chem. 1888, 38, 185–201. DOI: 10.1002/prac.18880380114.
- ↑ Revised nomenclature for radicals, ions, radical ions and related species (IUPAC Recommendations 1993). Pure Appl. Chem., 65 (6), 1367–1455. DOI: 10.1351/pac199365061357..
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