Heterocyclic replacement names

As described in Section 1.02.2.3, any heterocycle can be named by indicating (with appropriate prefixes) the positions of heteroatoms in the corresponding carbocycle. The carbocycle can be named systematically, as described in later Sections however, the replacement procedure can also be applied to naming heterocyclic analogues of trivially named carbocycles. A list of polycarbocycles with their trivial names is given in Table 5 (taken from Rule A-21.2 in the lUPAC Blue Book (B-79MI10200)) replacement names may be derived as shown in examples (27) and (28). As demonstrated by example (28), it is unnecessary to add hydro prefixes if the heterocycle cannot accommodate as many double bonds as the original carbocycle. 

In general, replacement prefixes should not be added to heterocyclic parent names, because of the resulting multiplicity of possible synonyms. For example, structure (27) should not be named 2,3,4,6-tetraazaindole or 3,4,6-triazaindazole without very good... 

Replacement nomenclature is used to name heteromonocycles that contain more than ten atoms. In developing a replacement name, carbon atoms are regarded as exchanged for heteroatoms. The non-detachable prefixes (Table 4.8) are used to indicate the exchange. Cycloalkane or annulene names are the bases for transformation into the name of a heterocycle. 

A heterocycle can be derived formally from a carbocycle by replacement of one or more carbon atoms with heteroatoms. In a replacement name, this is indicated by use of prefixes terminating in a, cited in the... 

Thus in many cases Stelzner replacement names require hydro- prefixes where the heterocyclic skeleton is in fact maximally unsaturated. This is a notable disadvantage, which often causes confusion, and the method is not recommended. 

Heterocyclic components can be given replacement names e.g., 49 would then be named spiro-[3//-l-azaindene-3,r-cyclopenta[2,4]diene]. Both types of method a spiro nomenclature are readily extensible to molecules containing more than one spiro linkage, e.g., 51 and 52. 

IUPAC Rules B-6 and B-10 give examples of heterocyclic cations named by replacement principles. The normal replacement prefixes... 

Thiathiophthene is a better choice, provided a locant be given to thia (6aIUPAC nomenclature to derive a replacement name from the trivial name of a heterocyclic system (thiophthene). 

Organic ring systems are named by replacement nomenclature. Three- to ten-membered mono-cyclic ring systems containing uncharged boron atoms may be named by the specialist nomenclature for heterocyclic systems. Organic derivatives are named as outlined for substitutive nomenclature. The complexity of boron nomenclature precludes additional details the text by Rigaudy and Klesney should be consulted. 

Sulfonium Compounds. Sulfonium compounds of the type R R R S X are named by citing in alphabetical order the radical names followed by -sulfonium and the name of the anion. For heterocyclic compounds, -ium is added to the name of the ring system. Replacement of > CH by sulfonium sulfur is denoted by the prefix thionia-, and the name of the anion is added at the end. 

Replacing one carbon atom of naphthalene with an a2omethene linkage creates the isomeric heterocycles 1- and 2-a2anaphthalene. Better known by their trivial names quinoline [91-22-5] (1) and isoquinoline [119-65-3] (2), these compounds have been the subject of extensive investigation since their extraction from coal tar in the nineteenth century. The variety of studies cover fields as diverse as molecular orbital theory and corrosion prevention. There is also a vast patent Hterature. The best assurance of continuing interest is the frequency with which quinoline and isoquinoline stmctures occur in alkaloids (qv) and pharmaceuticals (qv), for example, quinine [130-95-0] and morphine [57-27-2] (see Alkaloids). 

The absence of such a means for indicating hydrogenation of other monocyclic heterocycles forces the use of tetrahydro-, hexahydro- or perhydro- prefixes. The resulting names are, unfortunately, cumbersome, and in practice are inevitably replaced by acronyms, such as THF for tetrahydrofuran, when the substance must be referred to frequently. 

Heterocyclic rings may be named by considering them to be derived from hydrocarbons by replacing one or more carbon atoms by heteroatoms. The hydrocarbon corresponding to a particular heterocyclic system is found by formally replacing each hetero atom with... 

As noted in Section 1.02.3.2, replacement procedures can be applied to heterocyclic analogues of polycarbocycles named by fusion nomenclature. Examples (48) and (49) show... 

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