Hantzsch-Widman system
The Hantzsch-Widman system , sometimes also Hantzsch-Widman-Patterson system (after Arthur Hantzsch , Oskar Widman and Austin M. Patterson ), is a nomenclature system for the description of heterocyclic chemical compounds. The nomenclature is made up of two parts, one or more prefixes to identify the heteroatom (s) and an ending that refers to the ring size, saturation and, in some cases, the heteroatom. In addition to the systematic names, there are trivial names for certain compounds that existed before the introduction of nomenclature and are still preferred. Heteromonocycles with a ring size> 10, as well as simple, non-condensed spiro and bridged heterocycles, are named after the replacement nomenclature ("a" nomenclature).
history
In the years 1887 and 1888 Arthur Hantzsch and Oskar Widman were the first to set up rules for the nomenclature of heterocyclic compounds independently of one another. The basic idea of a combination of prefixes for the different heteroatoms and an ending for the ring size was identical for both and is still used today. The differences lay in the details, such as the order in which the heteroatoms are listed. Initially, the system only includes the five- and six-membered rings with oxygen , sulfur , selenium and nitrogen . It was then expanded to include more heteroatoms and ring sizes. In 1940 Austin M. Patterson published a systematic review of the nomenclature for the first time.
The Hantzsch-Widman nomenclature was officially included in the IUPAC nomenclature in 1957. Various changes were made after this as well, for example boron , which initially did not belong to it, was added to the nomenclature as a possible heteroatom.
Prefixes
Each heteroatom is given a unique term. This designation corresponds to the “a” nomenclature , in which the names of the heteroatoms always end with an “a”. If the next syllable of the compound name - as with the endings of the Hantzsch-Widman system - begins with a vowel, the "a" is omitted. The order of the individual heteroatoms is clearly defined by priorities based on the position of the element in the periodic table . This is important for naming systems that contain more than one heteroatom. The higher the number of the group of an element, the higher the priority. Within a group, the elements with a lower ordinal number have priority. This gives the highest priority for fluorine and other halogens , while metals have a low priority.
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Final syllables
The final syllable depends on the ring size and the saturation (number of double bonds ) in the ring system. Saturated compounds have no double bonds in the ring, unsaturated compounds have the maximum number of non-cumulative double bonds . In some cases the type of heteroatom also has an influence on the final syllable. In the case of the six-membered rings, a distinction is made between which heteroatom is in the ring. For this purpose, the heteroatoms are divided into three groups A, B and C. A includes oxygen, sulfur, selenium, tellurium, bismuth and mercury, B nitrogen, silicon, germanium, tin and lead, C boron, fluorine, chlorine, bromine, iodine, phosphorus, arsenic and antimony.
| Ring size | Ending unsaturated ring | Ending saturated ring |
|---|---|---|
| Three ring | -iren | -Iran |
| Four-ring | -et | - done |
| Five-membered ring | -oil | -olan |
| Six-ring (A) | -in | -on |
| Six-ring (B) | -in | -inan |
| Six-ring (C) | -inin | -inan |
| Seven-ring | -epin | -epan |
| Eight ring | -ocin | -ocan |
| Nine ring | -onine | -onan |
| Ten ring | -ecin | -ecan |
An exception in the nomenclature are nitrogen-containing, saturated rings with a ring size of three, four and five atoms. The endings -iridine (for three rings), -etidine (for four rings) and -olidine (for five rings) are used for these. In contrast to the nomenclature, the ending -irin is used for unsaturated, nitrogen-containing three-membered rings.
Heterocycles with several heteroatoms
If a heterocyclic compound contains several heteroatoms, the individual a-terms are listed one after the other. To do this, the individual heteroatom names are written one after the other in the order of the exchange nomenclature. If the system contains more than one identical heteroatom, a number syllable such as Di for two or Tri for three atoms is prefixed. With this system it is also possible to name cyclic compounds that have no carbon atoms.
1,4,2-oxazaphospholidine
1,3,6,4-thiadiazaborepane
Oxathiaphosphirane
At the same time, the system is numbered consecutively. In addition, the heteroatom with the highest priority receives the number one. It is then numbered in such a way that the heteroatoms are given the lowest possible digits.
- possible numbering
1,2,4-triazine (correct)
1,2,5-triazine (wrong)
1,3,4-triazine (wrong)
1,4,5-triazine (wrong)
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In the event that different end syllables would be required due to the different heteroatoms contained, the syllable used depends on the atom with the lowest priority, which is therefore listed last.
Condensed heterocycles
The nomenclature for condensed, i.e. unsaturated, heterocyclic compounds in which at least two rings are connected to one another via a common bond essentially corresponds to the nomenclature for condensed hydrocarbons.
The highest-ranking ring is used as the stem system and placed at the end of the name. The other rings or ring systems are then written as a prefix, specifying the point of connection in square brackets in front of the ring. To form the prefixes, the endings of the monocycles are replaced by an o. Some common names are shortened. Thus, from furan furo from quinoline quinone from pyridine pyrido from pyrimidine pyrimido and from thiophene thieno .
In order to clearly define the connection point, the point must be clearly defined both in the parent system and in the condensed system. To do this, both parts are numbered separately according to the rules for numbering cyclic systems. In the parent system, the bonds, beginning with the atom designated with 1, are designated with small letters a, b, c ... In the prefix system, however, the numbers in the numbering are retained. To indicate the point of connection, the position in the prefix system is first given in square brackets, then the letter of the root system is separated by a hyphen.
An exception are bicyclic systems in which one of the two rings is a phenyl ring. The linkage point is not specified for these, instead the heteroatoms are numbered so that the number 1 always designates an atom located directly next to the linkage point.
A sequence is defined which ring is used as the parent system in a system. The individual conditions are:
- Priority for heterocycles: if there is only one heterocycle next to several hydrocarbon rings, this always has priority and becomes the parent system
- Nitrogen-containing rings have priority: if there is a nitrogen-containing ring in addition to other heterocycles, this is used as the parent system
- Higher-ranking elements of the a-nomenclature have priority (except nitrogen): if rings with different heteroatoms are present in the system, the parent system used is the one that has the highest-ranking element in the table of the a-nomenclature
- Components with the greatest number of rings have priority: if there are several ring systems in which trivial names exist in whole or in part, the one in which the system to be named with the common names contains the most rings has priority
- Ring size: if the highest-ranking heteroatom is present in several rings, the largest ring has priority and becomes the parent system
- Number of heteroatoms: The ring in which a larger number of heteroatoms can be found has priority
- Diversity: The ring is chosen as the stem system in which a greater variety of rings occurs.
- larger number of preferred heteroatoms: the heterocycle that has more atoms of the heteroatom preferred according to the a-nomenclature becomes the parent system
- Smallest possible combination of ciphers: the smallest possible number should be achieved when naming the connecting bridge.
Individual evidence
- ↑ A. Hantzsch, JH Weber: About compounds of thiazole (pyridine of the thiophene series) . In: Reports of the German Chemical Society , 1887, 20, 2, pp. 3118–3132, doi : 10.1002 / cber.188702002200 .
- ^ O. Widman: On the nomenclature of compounds which contain nitrogen nuclei . In: Journal für Praktische Chemie , 1888, 38, 1, pp. 185-201, doi : 10.1002 / prac.18880380114 .
- ^ AM Patterson, LT Capell, The Ring Index , Reinhold, New York, 1940, pp. 20-21.
literature
- WH Powell: Revision of the extended Hantzsch-Widman System of nomenclature for heteromonocycles . In: Pure Appl. Chem. , 1983, 55, 2, pp. 409-416, pdf .
- D. Hellwinkel: The systematic nomenclature of organic chemistry . 5th edition, Springer, Heidelberg 2006, ISBN 978-3-540-26411-8 .