Extension of Hantzsch-Widman System. – Monocyclic compounds containing one or Fused Heterocyclic Systems · Replacement Nomenclature · Radicals. Hantzsch-Widmann nomenclature may be applied in the naming of unsaturated, as well as saturated, monocyclic heterocycles. According to this nomenclature. Devising a systematic nomenclature system for heterocyclic compounds The Hantzsch-Widman system provides a more systematic method of naming.

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Hantzsch—Widman nomenclaturealso called the extended Hantzsch—Widman systemis a type of systematic chemical nomenclature used for naming heterocyclic parent hydrides having no more than ten ring members. Hantzsch—Widman nomenclature is named after the German chemist Arthur Hantzsch and the Swedish chemist Oskar Widman, who independently proposed similar methods for the systematic naming of heterocyclic compounds in and respectively.

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 if there are several heteroatoms of the same type; and locants to indicate nomwnclature relative positions of the different atoms.

Hantzsch—Widman names may be combined with widkan aspects of organic nomenclature, to indicate substitution or fused-ring systems.

Hantzsch–Widman nomenclature

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 that hantzsvh higher on the list comes before the prefix that 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 substitutive nomenclaturebut Hantzsch—Widman nomenclature is recommended only for use with a more restricted set of heteroatoms see also below.

All of the prefixes end in “a”: In Hantzsch—Widman nomenclature but not in some other methods of naming heterocyclesthe 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. Hantzsch—Widman nomenclature, also called the extended Hantzsch—Widman system, is a type of systematic chemical nomenclature used for naming heterocyclic parent hydrides having no more than ten ring members.

The name hhantzsch include more than one prefix, if more than one type of heteroatom is present; a multiplicative prefix if there are several heteroatoms of Classification Although heterocyclic chemical compounds may be inorganic compounds or organic compounds, most contain at least one carbon.

While atoms that are neither carbon nor hydrogen are normally referred to in organic chemistry as heteroatoms, this is usually in comparison to the all-carbon backbone. But this does not prevent a compound such as borazine which has no carbon at Ideally, every possible organic compound should have a name from which an unambiguous structural formula can be created. To avoid long and tedious names in normal communication, the official IUPAC naming recommendations are not always followed in practice, except when it is necessary to give an unambiguous and absolute definition to a compound.

IUPAC names can sometimes be simpler than older names, as with ethanol, instead of ethyl alcohol. For relatively nomenclture molecules they can be more easily understood than non-systematic names, which must be learnt or looked up. However, the common or trivial name is often substantially shorter and clearer, and Azoles are a class of five-membered heterocyclic compounds containing a nitrogen atom and at least one other non-carbon atom i. The parent compounds are aromatic and have two double bonds; there are successively reduced analogs azolines and azolidines with fewer.

One, and only one, lone pair of electrons from each heteroatom in the ring is part of the aromatic bonding in an nomenclahure. Names of azoles maintain widmman prefix upon reduction e.

The numbering of ring atoms in azoles starts with the heteroatom that is not part of a double bond, and then proceeds towards the other heteroatom. Imidazole and other five-membered aromatic heterocyclic systems with two nitrogens are extremely common in nature and form the core of many biomolecules, such as histidine.


In chemistry thiadiazoles are a sub-family of azole compounds. Structurally they are five-membered heterocyclic compounds containing two nitrogen and a sulfur atoms, and two double bonds, to give an aromatic ring; with the name thiadiazole originating from the Hantzsch—Widman nomenclature. Four possible structures exist depending on the relative positions of the heteroatoms; these forms do not interconvert and hence are structural isomers and not tautomers. The compounds themselves are rarely synthesized and possess no particular application, however compounds bearing them nomehclature a structural motif are fairly common in pharmacology.

The prefix aza- is used in organic chemistry to form names of organic compounds where a carbon atom is replaced by a nitrogen atom. The related term “deaza-” refers to when a nitrogen is removed and, usually, a carbon atom is put in its place.

Sometimes a number between hyphens is inserted before it to state which atom the nitrogen atom replaces. It arose by shortening the word azote, which is an obsolete name for nitrogen in the English language and occurs in current French usage L’azotemeaning “Nitrogen”. This prefix is part of the Hantzsch—Widman nomenclature.

While the above figure gives examples of 4-aza steroids, 6-aza steroids have also been developed by GSK, although none of these compounds, as yet, are available for sale commercially.

Chemical structure of the 5- 4H -oxazolone isomer Oxazolone is a chemical compound and functional group, with the molecular formula CHNO. It was named in-line with the Hantzsch—Widman nomenclature and is part of a large family of oxazole based compounds. The 4-oxazolone motif, which is also formally a lactam, is present in a number of drugs fenozolone, thozalinone, cyclazodone, reclazepam etc. Pyridine is a basic heterocyclic organic compound with the chemical formula CHN.

The pyridine ring occurs in many important compounds, including azines and the vitamins niacin and pyridoxine.

Hantzsch-Widman Nomenclature

Pyridine was discovered in by the Scottish chemist Thomas Anderson hwntzsch one of the constituents of bone oil. Two years later, Anderson isolated pure pyridine through fractional distillation of the oil. It is a colorless, highly flammable, weakly alkaline, water-soluble liquid with a distinctive, unpleasant fish-like smell. Pyridine is used as a precursor to agrochemicals and pharmaceuticals and is also an important solvent and reagent.

Pyridine is hantszch to ethanol to make it unsuitable for drinking see denatured alcohol. It is used in the in vitro synthesis of DNA,[8] in the synthesis of sulfapyridine a drug against bacterial and viral infectionsantihistaminic drugs tripelennamine and mepyramine, as widmab as water Thiazolines or dihydrothiazoles are a group of isomeric 5-membered heterocyclic compounds containing both sulfur and nitrogen in the ring.

Although unsubstituted thiazolines are rarely encountered themselves, their derivatives are more common and some are bioactive. For example, in a common post-translational modification, cysteine residues are converted into thiazolines.

Isomers 2-Thiazoline, 3-Thiazoline and 4-Thiazoline from left to right Three structural isomers of thiazoline exist depending on the position of the double bond.

These forms do not readily interconvert and hence are not tautomers. Of these 2-thiazoline is the most common.

A fourth structure exists in which the N and S atoms are adjacent; this known as isothiazoline. Synthesis Thiazolines were first prepared by dialkylation of thioamides by Richard Willstatter in Oxazoline is a five-membered heterocyclic chemical compound containing one atom each of oxygen and nitrogen.

It was likely first synthesized in [2] but it was not until 5 years later that Siegmund Gabriel correctly assigned the structure. Oxazoline itself has no current applications however compounds containing the ring, which are referred to as oxazolines or oxazolyls, have a wide variety of uses; particularly as ligands in asymmetric catalysis, as protecting groups for carboxylic acids and increasingly as monomers for the production of polymers.

Hantzsch may refer to: Benzodiazepines BZD, BDZ, BZssometimes called “benzos”, are a class of psychoactive drugs whose core chemical structure is the fusion of a benzene ring and a diazepine ring.

The first such drug, chlordiazepoxide Libriumwas discovered accidentally by Leo Sternbach inand made available in by Hoffmann—La Roche, which, sincehas also marketed the benzodiazepine diazepam Valium. High doses of many shorter-acting benzodiazepines may also cause anterograde amnesia and dissociation. A chemical nomenclature is a set of rules to generate systematic names for chemical compounds.

A third publication, known as the Green Book,[3] describes the recommendations for the use of symbols for physical quantities in association with the IUPAPwhile a fourth, the Gold Book,[4] contains the definitions of a large number of technical terms used in chemistry. These “color books” are supplemented by shorter recommendations for specific circumstances that are published periodically Arsole, also called arsenole[1] or arsacyclopentadiene, is an organoarsenic compound with the formula CHAsH.


It is classified as a metallole and is isoelectronic to and related to pyrrole except that an arsenic atom is substituted for the nitrogen atom. Whereas the pyrrole molecule is planar, the arsole molecule is not, and the hydrogen atom bonded to arsenic extends out of the molecular plane.

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Arsoles and more complex arsole derivatives have similar structure and chemical properties to those of phosphole derivatives. When arsole is fused to a benzene ring, this molecule is called arsindole, or benzarsole. The naming of cyclic organoarsenic compounds such as arsole is based on an extension of the Hantzsch—Widman nomenclature system[4] approved Nomencllature IUPAC nomenclature, a parent hydride is an unbranched acyclic or cyclic structure to which only hydrogen atoms are attached.

They are the basic structures used no,enclature substitutive nomenclature.

The bonding number of a skeletal atom in a parent hydride is the sum of the total number of valence bonds to adjacent skeletal atoms, if any, and the number of attached hydrogen atoms.

In SH, for example, S has bonding number 2. Parent hydrides in substitutive nomenclature Parent hanttzsch are compounds with an unsubstituted skeleton, thus with only hydrogens attached to it.

They have a defined standard population of hydrogen atoms. Acyclic parent hydrides are always saturated and unbranched. Cyclic parent hydrides are usually either fully saturated or fully unsaturated containing the maximum number of double bonds.

A cyclic compound ring compound is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where all the atoms are carbon i.

Depending on the ring size, the bond order of the individual links between ring atoms, and their arrangements within the rings, nomenclaturd and heterocyclic compounds may be hanzsch or non-aromatic, in the latter case, they may vary nomrnclature being fully saturated to having varying numbers of multiple bonds between the ring atoms.

Because of the tremendous diversity hntzsch, in combination, by the valences of common atoms and their ability to form rings, the number of possible cyclic structures, even of small size e. Chemical nomenclature, replete as it is with compounds with complex names, is nomenclatkre repository for some very peculiar and sometimes startling names. A browse through the Physical Constants of Organic Compounds in the CRC Handbook of Chemistry and Physics a fundamental resource will reveal not just the whimsical work of chemists, but the sometimes peculiar compound names that occur as the consequence of simple juxtaposition.

Some names derive legitimately from their chemical makeup, from the geographic region where they may widmsn found, the plant or animal species from which they are isolated or the name of the discoverer. Some are given intentionally unusual trivial names based on their structure, a notable property or at the whim of those who first isolate them.

However, many trivial names predate formal naming conventions.

Trivial names can also be ambiguous or carry different meanings in different industries, geographic regions and languages. Telluropyrylium is an aromatic heterocyclic compound consisting of a six member ring with five carbon atoms, and a positively charged tellurium atom. However this is misleading, as “tellura” indicates that tellurium substitutes for carbon atom, but actually tellurium is substituted for the oxygen atom in pyrilium.

This is the name used by Chemical Abstracts. Replacement nomenclature would call this telluroniabenzene. Occurrence Because telluropyrylium is a positively charged cation, it takes the sol Selenopyrylium is widmann aromatic heterocyclic compound consisting of a six member ring with five carbon atoms, and a positively charged selenium wwidman.