Prefixes Hantzsch-Widman system

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). 

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. 

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. 

As lactones are cyclic esters, so lactams are cyclic amides. Again, as was the case with lactones, the nomenclature of the lactams is based on the use of Greek letters to show ring size, substitution of nitrogen for carbon in a cyclic array (thus using the prefix azacyclo ), or the Hantzsch-Widman system (vide supra). Some examples follow in Table 5.14. 

Hantzsch-Widman name a name devised by Hantzsch and Widman for describing heterocyclic systems, in which the prefix denotes a hetero atom(s) and the suffix denotes the ring size and degree of saturation e.g., oxirene, aziridine. 

Hantzsch-Widman names are used for one-ring heterocyclic systems that do not have trivial names. The names are applied to monocyclic compounds containing one or more heteroatoms in three- to ten-membered rings. The names are derived by combining the appropriate prefix or prefixes for the heteroatoms with a stem denoting the size of the ring (see below). The state of hydrogenation is indicated either in the stem or by the prefixes dihydro-, tetrahydro-, etc. 

Owing to the numerous possibilities in which a 1,4-diene can be assembled, especially when heteroatoms are included, a nomenclature issue arises that needs to be addressed from the outset. According to the Hantzsch-Widman nomenclature system in combination with the lUPAC rules, hetera-di-ir-meth-ane reactions are those transformations in which a particular heteroatom replaces the caiixin atom of the 1,4-diene moiety the position is specified by means of a numerical prefix. We will use this suggested nomenclature for the di-Tr-methane photorearrangement as indicated for the substrates shown in Scheme 1. 

For cyclic systems, the prefix cyclo in connection with the name of the corresponding chain compound, or the Hantzsch-Widman (H-W) nomenclature system (see Section IR-6.2.4.3), may be used. 

At this point, we can introduce an entirely different system of nomenclature that is nevertheless accepted by lUPAC and is extremely valuable in multicyclic and bridged saturated systems. This is the replacement system, where the hydrocarbon name that would correspond to the entire ring structure, as if no heteroatom were present, is stated, and then given a Hantzsch-Widman prefix and number for the heteroatom(s). Thus, phenanthridine shown previously has the ring framework of the hydrocarbon phenanthrene, with N at position 5. The replacement name would be 5-azaphenanthrene. 

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