Hantzsch - Widman system

The Hantzsch - Widman system serves for the nomenclature of heterocyclic compounds. The affixes for the Hantzsch - Widman system are shown in Table 14.2. 

The system tries to name heterocyclic compounds so that several well-known heterocyclic compounds are named in the same way or at least very similar as their corresponding trivial name. For example, ethylene oxide is oxiran. Other examples are dioxan and dioxin. The systematic name for sulfolane would be thiolan. 

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Hansa Yellows, 1, 334 5, 299 Hantzsch synthesis, 2, 87-88 1,4-dihydropyridine, 2, 482 thiazoles, 6, 294-299 A -thiazolines, 6, 314 Hantzsch-Widman names parent names, 1, 35 stem suffixes, 1, 12 Hantzsch-Widman system nomenclature, 1, 11-12 Hardeners in photography... 

For such purposes as locating substituents, monocyclic heterocycles having only one non-carbon atom are numbered starting with the hetero atom as 1. If there is more than one hetero atom of the same kind, the more saturated hetero atom takes precedence (cf. imidazole in Table 1). In isoxazole and isothiazole, the divalent atom takes precedence, in conformity with the pnaciples of the Hantzsch-Widman system (Section 1.02.2.2). 

There are 19, largely nonmetallic, elements encompassed by the Hantzsch-Widman system the prefixes to indicate them are shown in Table 2. These prefixes, all of which end in a (which may be lost by elision), are the same as those used in replacement nomenclature (Section 1.02.2.3). 

For single rings (i.e. mononuclear systems) up to ten atoms in size, there is no question but that Hantzsch-Widman names are overwhelmingly the most widely used, and specialists can be presumed to recognize them readily. However, when one of the trivial names of Table 1 can be used, it prevails almost exclusively. Thiophene will be immediately understood by specialists and most nonspecialists, whereas thiole will distract the reader s attention from the chemistry while he considers the writer s intention is the Hantzsch-Widman system indeed being used, or is it a typographical error Chemical Abstracts also uses these trivial names in its indexes. 

According to the Hantzsch-Widman system, the seven-membered unsaturated hcterocyclc with one sulfur atom is named thiepin (1). The three different benzothiepins are assigned by the position of sulfur 1-benzothiepin (2), 2-benzothiepin (3) and 3-benzothiepin (4). Of the four possible dibenzothiepins only dibenzo[6,r/]thiepin (5) and dibenzo[A,/]thiepin (6) are of importance for synthesis, while the other two isomers, which contain unfavorable o-quinoid structures, exist mainly as the stable dihydro compounds, i.c. 5,7-dihydrodibenzo[c,t ]thiepin (7) and 6,1 l-dihydrodibenzo[6,c ]thiepin (8). Benzannulation over all double bonds results in tri-benzo[6,(7,/]thiepin (9). 

IUPAC Commission on Nomenclature of Organic Chemistry, Revision of the extended Hantzsch-Widman system of nomenclature for heteromonocycles, Pure Appl. Chem., 55, 409-416 (1983). 

The nomenclature of boron compounds involves some intricacies. IUPAC rules allow the terms borabenzene or borinine for 2 the older name borin has become obsolete with the recent revision of the extended Hantzsch-Widman system (6). Anions 4 are termed boratabenzene ions an alternative would be borininate instead of the earlier borinate (7). 

The two most important methods for naming heterocyclic parent hydrides are the extended Hantzsch-Widman system and replacement nomenclature. 

The extended Hantzsch-Widman system is used to name monocycles of saturated and mancude rings with between three and ten members, inclusive. The names are composed of two parts non-detachable prefix(es), indicating the heteroatom and a stem indicating the size of the ring. Names of prefixes (called a prefixes) are listed in Table 4.8 and names of stems in Table 4.9. 

This method is useful when dealing with simple heterocycles, but it can become clumsy with more complex ones. An alternative is the Hantzsch-Widman system, which uses the same prefixes, but adds a stem name designed to indicate not only the ring size but also the state of unsaturation or saturation (note when the stem name begins with a vowel the last letter, a, of the prefix is dropped). The stem names for rings containing up to 10 atoms are shown in Table 1.1. 

Hantzsch-Widman System of Nomenclature for Heteromonocycles, Pure Appl. 

Extended Hantzsch-Widman System for Monocycles (IUPAC Rule... 

The Hantzsch-Widman system provides names for both fully saturated and fully unsaturated molecules. Partially saturated molecules are named by attaching appropriate hydro prefixes to the names of the fully saturated rings however the special suffixes applicable to four-and five-membered rings may also be used (this is not now recommended... 

Some complications arise with certain heteroatoms when strict application of the Hantzsch-Widman system could lead to confusion in these cases prefixes or suffixes are suitably modified, e.g., 63-66. 

SPECIALIST HETEROCYCLIC NOMENCLATURE Rule B-l. Extension of Hantzsch-Widman System... 

Numbering of the ring starts with the hetero atom and proceeds around the ring so as to give substituents (or other hetero atoms) the lowest numbered positions. When two or more different hetero atoms are present, oxygen takes precedence over sulfur and sulfur over nitrogen for the number one position. Examples follow to illustrate both the heterocycloalkane and the Hantzsch-Widman systems. Trivial names also are included. 

Although Hantzsch-Widman system works satisfactorily (if you can remember the rules) for monocyclic compounds, it is cumbersome for polycyclic compounds. In the case of oxiranes it is simplest for conversational purposes to name them as oxides of the cycloalkenes or epoxy derivatives of the corresponding cycloalkanes. The oxabicycloalkane names seem preferable for indexing purposes, particularly because the word oxide is used in many other connections. 

Another example of the prevailing use of "unnecessary" affixes in IUPAC inorganic nomenclature occurs in the extended Hantzsch-Widman system. Here a Greek capital delta (A) is inserted to denote a double bond in a heterocyclic ring. For example, the four-member ring which IUPAC would name as A3-l, 2-Azarsetine (Figure 27) in the proposed system is simply ... 

Type of heteroatom, according to the Hantzsch-Widman system (O, S, N, P). 

The Hantzsch Widman system is often used for the nomenclature of organic rings. This indicates the ring size by specific sufSxes the first suffix given is used for saturated rings, the second for unsaturated rings ... 

Several modifications were later made in order to avoid confusion with other compounds for example, phosphorine was used instead of phosphine. The modified (extended) Hantzsch-Widman system (Pure Appl. Chem., 55,409,1983) uses the stems shown in Table 4.3. 

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