Hantzsch–Widman nomenclature, also called the extended Hantzsch–Widman system, is a type of systematic

Systematic name

A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection...

 chemical nomenclature

IUPAC nomenclature of organic chemistry

The IUPAC nomenclature of organic chemistry is a systematic method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry . Ideally, every possible organic compound should have a name from which an unambiguous structural formula can be drawn. ...

 used for naming heterocyclic parent hydride

Parent hydride

In IUPAC nomenclature, a parent hydride is an unbranched acyclic or cyclic structure to which only hydrogen atoms are attached. Parent hydrides are parent structures that contain one or more hydrogen atoms...

s having no more than ten ring members.
Some common heterocyclic compounds have retained name

Retained name

In chemistry, a retained name is a name for a chemical compound that is recommended for use by a system of chemical nomenclature , but that is not fully systematic....

s which do not follow the Hantzsch–Widman pattern.

Hantzsch–Widman nomenclature is named after the German chemist Arthur Hantzsch

Arthur Rudolf Hantzsch

Arthur Rudolf Hantzsch , was a German chemist.-Life and work:Hantzsch studied chemistry in Dresden and graduated at the University of Würzburg under Johannes Wislicenus...

 and the Swedish chemist Oskar Widman, who independently proposed similar methods for the systematic naming of heterocyclic compounds in 1887 and 1888 respectively. It forms the basis for many common chemical names, such as dioxin and benzodiazepine

Benzodiazepine

A benzodiazepine is a psychoactive drug whose core chemical structure is the fusion of a benzene ring and a diazepine ring...

.

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

Double bond

A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...

s. The name may include more than one prefix, if more than one type of heteroatom is present; a multiplicative prefix if 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 Fluorine Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...	fluora	Arsenic Arsenic Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...	arsa
Chlorine Chlorine Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...	chlora	Antimony Antimony Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...	stiba
Bromine Bromine Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...	broma	Bismuth Bismuth Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...	bisma
Iodine Iodine Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....	ioda	Silicon Silicon Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...	sila
Oxygen Oxygen Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...	oxa	Germanium Germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....	germana
Sulfur Sulfur Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...	thia	Tin Tin Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...	stanna
Selenium Selenium Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...	selena	Lead Lead Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...	plumba
Tellurium	tellura	Boron Boron Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...	bora
Nitrogen Nitrogen Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...	aza	Mercury Mercury (element) Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...	mercura
Phosphorus Phosphorus Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...	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

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

) always comes before "aza" (for nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

) in a name. The priority order is the same as that used in substitutive nomenclature, but Hantzsch–Widman nomenclature is only recommended for use with a more restricted set of heteroatoms (see also below).The 2004 Draft Recommendations propose adding aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 (aluma), gallium

Gallium

Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...

 (galla), indium

Indium

Indium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two...

 (indiga) and thallium

Thallium

Thallium is a chemical element with the symbol Tl and atomic number 81. This soft gray poor metal resembles tin but discolors when exposed to air. The two chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861 by the newly developed method of flame spectroscopy...

 (thalla) to the list of heteroatoms for which Hantzsch–Widman nomenclature is used, and removing mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

.

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

Elision

Elision is the omission of one or more sounds in a word or phrase, producing a result that is easier for the speaker to pronounce...

 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

Halogen

The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...

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. In principle, lambda nomenclature could be used to specify a non-standard valence state

Valence (chemistry)

In chemistry, valence, also known as valency or valence number, is a measure of the number of bonds formed by an atom of a given element. "Valence" can be defined as the number of valence bonds...

 for a heteroatom 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
  Double bond
  A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...
  
  s;
• the nature of the heteroatoms

Notes on table:

1. Heteroatom priority is increasing as follows: F, Cl, Br, I, O, S, Se, Te, N, P, As, Sb, Bi, Si, Ge, Sn, Pb, B, Al, Ga, In, Tl, Hg.
2. Names in parenthesis indicate ending when nitrogen is present

   Ring size		Saturated	Unsaturated
   3		-irane (-iridine)	-irene (-irine)
   4		-etane (-etidine)	-ete
   5		-olane (-olidine)	-ole
   6A	O, S, Se, Te; Bi, Hg	-ane	-ine
   6B	N; Si, Ge, Sn, Pb	-inane
   6C	B; F, Cl, Br, I; P, As, Sb		-inine
   7		-epane	-epine
   8		-ocane	-ocine
   9		-onane	-onine
   10		-ecane	-ecine

External links

• Hantzsch-Widman nomenclature, IUPAC