This restriction does not apply to suffixes denoting unsaturation, such as "-ene" and "-yne" (see R-3.1), which are not regarded as principal characteristic groups; nor to the ionic and
radical suffixes, such as "-ium", "-ide", and "-yl" (see R-188.8.131.52), which may be combined and may also be added to certain principal characteristic group suffixes, for example,
ethanaminium and pyridin-1-ium-3-yl.
This HTML reproduction is as close as possible to the published version [see IUPAC, Commission on Nomenclature of Organic Chemistry. A Guide to IUPAC Nomenclature of Organic Compounds
(Recommendations 1993), 1993, Blackwell Scientific publications, Copyright 1993 IUPAC]. If you need to cite these rules please quote this reference as their source.
Published with permission of the IUPAC by Advanced Chemistry Development, Inc., www.acdlabs.com, +1(416)368-3435 tel, +1(416)368-5596 fax. For comments or suggestions please contact firstname.lastname@example.org