Replacement prefixes

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... 

Such structures are most simply named by the replacement method, using the ending -onia instead of -a in the replacement prefixes. In the examples, such names are compared with A-ylium names, which are derived quite differently. 

Meanwhile, the A convention combined with replacement nomenclature may be used to indicate the changed bonding number of the anionic site, and the suffix -ide appended, as shown in (202) and (203). Proposals for an anionic replacement prefix, analogous to the cationic -onia prefixes, are under consideration. 

The methods for naming cations and anions may be combined to name zwitterions the cationic center is cited before the anionic center, both in the replacement prefixes and in the suffixes, e.g. (204). One should be aware, however, that Chemical Abstracts names zwitterions by an extraordinary circumlocution, in which water is hypothetically added and then hypothetically taken away, to give names consisting of four separate words ending in inner salt, e.g. (205). 

Spiro systems can be named by normal procedures [13]. For clarity, any anhydro or deoxy prefixes or chalcogen replacement prefixes (e.g. thio) referring to the spiro... 

Structures in which the linking glycosidic oxygen is replaced by -CH2- may be named by use of the replacement prefix carba- (c/. 2-Carb-34.2) for emphasis of homomorphic relationships. The oxygen replaced is given the locant of the carbon atom to which it is attached in the residue with the lower roman numeral (cited as superscript) (cf 2-Carb-37.2), with suffix a1. 

Examples of Replacement Prefixes (in Descending Order of Priority)"... 

In using replacement nomenclature it is imperative to apply replacement prefixes only to a carbocyclic parent name, never to a heterocyclic... 

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

Replacement, e.g., azacyclotridecane. Organic replacement names are formed by denoting heteroatoms that replace skeletal atoms of a hydrocarbon molecular skeleton by organic replacement prefixes (Table 3.4). In nomenclature, the prefixes are cited in the order they are given in the table. 

This occurs when one or more oxygen atoms in a functional group are notionally replaced by other heteroatoms. Depending on the hierarchy, this may lead to the use of functional replacement prefixes (e.g., seleno in selenoacetic acid, H3C-C(=Se)OH), infixes, or suffixes (e.g., in benzenecar-bodithioic acid, Ph-C(=S)-SH). 

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. 

In this method, the chain is named first as if it were composed entirely of carbon atoms. Any heteroatoms in the chain are then designated by appropriate replacement prefixes ( a terms) from Table X cited in the order given by Table VI, each preceded by its appropriate locant. The locants are assigned by numbering the chain from that end which gives lower locants to the heteroatom set as a whole and, if these are equal, from that end which gives the lower locant or locant set to the replacement prefix first cited. If there is still a choice, lower locants are assigned to the sites of unsaturation. 

Use the carbocyclic ring name with heteroatom replacement prefixes oxa-, thia-, and so forth. 

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