Editing Functional group (section)

===Names of radicals or moieties===
These names are used to refer to the moieties themselves or to radical species, and also to form the names of halides and substituents in larger molecules.

When the parent hydrocarbon is unsaturated, the suffix ("-yl", "-ylidene", or "-ylidyne") replaces "-ane" (e.g. "ethane" becomes "ethyl"); otherwise, the suffix replaces only the final "-e" (e.g. "[[ethyne]]" becomes "[[ethynyl]]").<ref name="qmul"/>

When used to refer to moieties, multiple single bonds differ from a single multiple bond. For example, a [[methylene bridge]] (methanediyl) has two single bonds, whereas a [[methylidene group]] (methylidene) has one double bond. Suffixes can be combined, as in methylidyne (triple bond) vs. methylylidene (single bond and double bond) vs. methanetriyl (three double bonds).

There are some retained names, such as [[methylene group|methylene]] for methanediyl, 1,x-[[phenylene]] for phenyl-1,x-diyl (where x is 2, 3, or 4),<ref>{{cite web|url=https://www.acdlabs.com/iupac/nomenclature/93/r93_271.htm|title=R-2. 5 Substituent Prefix Names Derived from Parent Hydrides|publisher=IUPAC|year=1993|access-date=2018-12-15|archive-date=2019-03-22|archive-url=https://web.archive.org/web/20190322061930/https://www.acdlabs.com/iupac/nomenclature/93/r93_271.htm|url-status=live}} section P-56.2.1</ref> [[carbyne]] for methylidyne, and [[trityl]] for triphenylmethyl.

{| class="wikitable"
|-
! [[Chemical class]] !! Group !! Formula !! Structural formula !! Prefix !! Suffix !! Example
|-
| Single bond || || R• || || Ylo-<ref>{{cite web|url=http://www.chem.qmul.ac.uk/iupac/ions/RC813.html|title=Revised Nomenclature for Radicals, Ions, Radical Ions and Related Species (IUPAC Recommendations 1993: RC-81.3. Multiple radical centers)|access-date=2014-12-02|archive-url=https://web.archive.org/web/20170611171918/http://www.chem.qmul.ac.uk/iupac/ions/RC813.html|archive-date=2017-06-11|url-status=dead}}</ref> || -yl || {{center|[[Methyl group]]<br>[[Methyl radical]]}}
|-
| Double bond || || R: || || ? || -ylidene || {{center|[[Methylidene]]}}
|-
| Triple bond || || R⫶ || || ? || -ylidyne || {{center|[[Methylidyne]]}}
|-
| Carboxylic [[acyl]] radical || Acyl || R−C(=O)• || || ? || -oyl || {{center|[[Acetyl]]}}
|}