Infixes, functional replacement

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). 

Non-acidic functional replacement analogues are named by replacing the word acid with the appropriate class name occurring earliest in the following list hydrazide, halide, azide, amide, cyanide, nitride, imide. Other replacing groups are denoted by infixes, as described earlier for acidic functional replacement analogues. The examples below are derived from phosphoric acid. 

A problem that would arise with the general use of the prefix variant of functional replacement names is illustrated by the thio acids. The names trithiocarbonic acid, tetrathiophosphoric acid, etc., would lead to anion names trithiocarbonate, tetrathiophosphate, etc., which appear to be additive names but are incorrect as such because the ligand prefix is now sulfido or sulfanediido [thus giving trisulfidocarbonate(2—),tetrasulfidophosphate(3—), etc.]. Section P-65.2 of Ref. 1 prescribes the infix-based name carbonotrithioic acid, leading to the anion name carbonotrithioate, which will not be mistaken for an additive name. 

Terminal vowel of infixes used in functional replacement nomenclature (Section IR-8.6) to indicate replacement of oxygen atoms and/or hydroxy groups, e.g. amido , nitrido , thio . 

If one hydrogen is removed from an alkane, the residue is called an alkyl group. The -ane suffix is replaced by an -yl- infix when this residue is used as functional group. Functional groups are used to systematically build up the names of organic molecules. 

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