Hantzsch–Widman nomenclature

The Hantzsch - Widman system, sometimes also Hantzsch - Widman system Patterson ( Arthur Hantzsch, Oskar Widman and Austin M. Patterson ) is a nomenclature system for description of heterocyclic chemical compounds. The nomenclature consists of two parts, one or more prefixes to identify the or of the heteroatom and the ending that refers to ring size, saturation, and partly also the heteroatom. In addition to the systematic names there are for certain compounds Trivial names existed prior to introduction to the nomenclature and still preferred.

History

In the years 1887 and 1888 rules were independently assessed by Arthur Hantzsch and Oskar Widman first proposed the nomenclature of heterocyclic compounds. The basic idea of a combination of prefixes for the various heteroatoms and an ending for the ring size was the same for both and is used to this day. The differences lay in the details, such as the order in which the heteroatoms are enumerated. First, the system includes only the five - and six-membered rings of oxygen, sulfur, selenium, and nitrogen. It was then extended to other heteroatoms and ring sizes. 1940 Austin M. Patterson published the first systematic overview of the nomenclature.

Officially in the nomenclature of the IUPAC the Hantsch - Widman nomenclature 1957 has been included. Even after this was changed different, the first not to belong boron was added as a possible heteroatom in the nomenclature.

Replacement nomenclature

Each heteroatom is called with a unique concept. This nomenclature is called replacement nomenclature or a nomenclature. The name of a nomenclature stems from the fact that the names of the heteroatoms always end with an a. If the next syllable of the composite name - as the extensions of the Hantzsch - Widman system - begins with a vowel, the a is omitted. This nomenclature also determines a unique sequence of the individual heteroatoms. This is for naming systems containing more than one hetero atom is important. The priority is determined on the basis of the periodic table. The higher the group number of an element, the higher the priority. Within a group, the elements with a smaller ordinal priority. This results in the highest priority for fluorine and other halogens, while metals have a low priority.

Final syllables

The final syllable is determined by the ring size and after saturation ( number of double bonds ) in the ring system. Saturated compounds having no double bonds in the ring unsaturated, the maximum number of noncumulative double bonds. In some cases also the type of the hetero atom to influence the final syllable. Especially when the six-membered rings, it is discriminated which is a heteroatom in the ring. To the heteroatoms in the three groups A, B and C are divided. A includes oxygen, sulfur, selenium, tellurium, bismuth and mercury, B is nitrogen, silicon, germanium, tin and lead, C boron, fluorine, chlorine, bromine, iodine, phosphorus, arsenic and antimony.

An exception in the nomenclature are nitrogen- containing saturated rings with a ring size of three, four and five atoms. For this, the endings - iridin be ( for three rings), etidin ( for four rings ) and olidin used ( for five-membered rings ). For unsaturated nitrogen-containing three-membered rings the ending- irin is different from the nomenclature used.

Heterocycles having more heteroatoms

A heterocyclic compound are more heteroatoms, the individual A- terms are enumerated in succession. The individual heteroatom names are written in order of replacement nomenclature succession. If more than one hetero atom included in the same system, a number of syllables, such as di or tri two is preceded by three atoms. It is also possible with this system to designate cyclic compounds having no carbon atoms.

1,3,6,4 - Thiadiazaborepan

Oxathiaphosphiran

At the same time, the system is numbered. To get the heteroatom with the highest priority, the number one. Then be numbered so that the heteroatoms get the lowest possible numbers.

• Possible numberings

1,2,5- triazine (false )

1,3,4- triazine (false )

1,4,5- triazine (false )

In the event that would make it through various heteroatoms contained different suffixes required, the syllable used depends on the atom with the lowest priority, so that will be listed last.

Fused heterocycles

The nomenclature of fused, ie unsaturated heterocyclic compounds in which at least two rings are joined together by a common bond, corresponds to substantially the nomenclature of condensed hydrocarbons.

There the highest- ring is used as the root system and placed at the end of the name. Then the other rings or ring systems can be written as a prefix indicating the point of attachment in brackets before the ring. To form the prefixes, the endings of the monocycles is a O is replaced. Some common names are shortened. Thus, from furan furo, from quinoline quinone selected from pyridine, pyrido, pyrimido of pyrimidine and thieno from thiophene.

To clearly define the point of attachment, the place to be uniquely determined both in the root system, as well as in the condensed system. These two parts are numbered separately according to the rules for numbering of cyclic systems. The family system, the bonds, ranging from marked 1 atom, with small letters a, b, c, ... respectively. In the Prefix system, however, the figures of the numbers is retained. To specify the point of attachment, the situation inside the brackets initially specified in the prefix system, followed by a hyphen, the letter of the root system.

An exception are bicyclic systems wherein one of the two rings is a phenyl ring. In these, the point of attachment is not specified, the heteroatoms are instead numbered so that with the number 1 always be placed directly inside next to the point of attachment atom is referred to.

It is defined a sequence, which ring is used in a system as the root system. The conditions are as follows in sequence:

• Priority of heterocycles: if only a heterocycle present in addition to more hydrocarbon rings, this always has priority and is the root system
• Nitrogen-containing rings have priority: in addition to other heterocycles also a nitrogen-containing ring exists, it is used as the root system
• Rank Higher elements of a nomenclature have priority (except nitrogen ) are rings with different heteroatoms in the system, one is used as the root system, which has the highest-ranked element in the table of a nomenclature
• Components with the most rings have priority: more ring systems are available in which all or part of trivial names exist, those which take precedence, in which the specifically designated with trivial name system contains most of the rings has
• Ring Size: is the highest-ranking heteroatom in several rings available, the largest ring has priority and is the root system
• Number of heteroatoms: Priority has one ring in which a larger number can be found on heteroatoms
• Diversity: the ring is chosen as the root system in which occurs a greater variety of rings.
• Larger number privileged ended heteroatoms: the heterocycle which has more atoms of the privileged after a nomenclature hetero atom, is the root system
• Smallest possible code combination: it is to be achieved in the naming of the bridge connecting the smallest possible number.