To minimize confusion the following terms are used in the present rules:
Functional class name: a word such as ketone, chloride, or alcohol, used in radicofunctional nomenclature (according to the language) as an ending or as a separate word (see Rules C-21 to C-24).
Substituent: any atom or group replacing hydrogen of a parent compound.
Characteristic group: an atom or group that is incorporated into a parent compound otherwise than by a direct carbon-carbon linkage, but including groups and >C=X where X is O, S, Se, Te, NH, or substituted NH. (N.BThe phrase "characteristic group" includes both groups such as OH, NH2, COOH, and single atoms such as halogen, =O, and It does not apply to substituents such as methyl, phenyl, 2-pyridyl, but does include, for example, piperidino and acetyl.)
Principal group: the characteristic group chosen for expression as suffix in a particular name. (This is equivalent to the "principal function" of the Liege rules.)
See Recommendations'93 R-0.2
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