Hantzsch-Widman names

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... 

Table 3 Stem Suffixes for Hantzsch-Widman Names ...

The lUPAC recommendations regarding the Hantzsch-Widman names are not intended to supersede the commonly used traditional, trivial names listed in Table 1. 

It is apparent that replacement names can be formed for rings of alt sizes, and the rules for forming them are simple. On the other hand, the names are usually quite long, and as a consequence, chemists more often than not avoid such names in favor of recognized trivial names or Hantzsch-Widman names for ring sizes for which they are available. Examples are given in (17)-(20). 

The prefixes to be attached to the name of the base component are formed by changing the terminal e of the trivial or Hantzsch-Widman names of the components (in the form containing the maximum number of non-cumulative double bonds) into o . Some prefixes are further abbreviated, as exemplified in the following list ... 

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. 

Oxepin is the Hantzsch-Widman name for a seven-membered unsaturated heterocycle with one oxygen atom and the numbering follows the convention for monocyclic heterocycles. However, the isomeric benzene oxide has different numbering in agreement with the 7-oxabi-cyclo[4.1.0]hepta-2,4-diene structure, position 1 now corresponds to position 2 in the oxepin. 

In one method, the non-detachable prefixes hydro- and dehydro- (in the case of mancudes only) can be used to indicate the addition or subtraction of one hydrogen atom. As even numbers of hydrogen atoms are involved when a carbon-carbon single bond becomes a double or triple bond, the multiplicative prefixes di-, tetra-, etc., as well as the appropriate locants, are used. The prefix dehydro- is always used to indicate the subtraction of hydrogen atoms from saturated heterocycles having Hantzsch-Widman names. 

IUPAC/Chemical Abstracts System (IUPAC Rule B-3). The fusion operations described in Section II, A, 3, a are applied to trivial and/or Hantzsch-Widman names of heterocyclic (and, if present, car-bocyclic) components see examples 25-27. In addition a unit consisting of a benzene ring fused to a one-ring heterocycle can be considered as a single component. If this one-ring heterocycle contains 3-10 members it... 

Methods for naming homogeneous rings and rings of repeating units consisting entirely of heteroatoms are outlined in the IUPAC 1973 Tentative Rules (Section D).8 Such molecules can, of course, be named by strict replacement principles, and most organic chemists will doubtless wish to use replacement names for them. (Hantzsch-Widman names could also be used.) However, this practice may seem unreasonable in... 

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. 

Heterocyclic systems can be named by various methods, depending on ring size, the presence or absence of metal atoms, the availability of trivial names, etc. For this index the naming of the heterocyclic parents has generally followed the practices of IUPAC and Chemical Abstracts. Thus Hantzsch-Widman names have been employed for all monocyclic systems and for the other systems when the smallest ring size is five atoms or more, but replacement nomenclature has usually been followed for bicyclic and higher systems when they contain three- and four-membered rings. 

Table 1 Stem suffixes for Hantzsch-Widman names...

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. 

The prefixes are the normal replacement prefixes (see Replacement Nomenclature, page 50), although elision of the final a often occurs. The prefixes are cited in the following order fluora-, chlora-, broma-, ioda-, oxa-, thia-, selena-, tellura-, aza-, phospha-, bora-, and mercura-. Chemical Abstracts does not use Hantzsch-Widman names for rings containing silicon. 

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