Editing Substituent (section)

== Nomenclature ==
The [[affix|suffix]] ''-yl'' is used in [[organic chemistry]] to form names of [[radical (chemistry)|radical]]s, either separate species (called ''free radicals'') or chemically bonded parts of molecules (called ''[[moiety (chemistry)|moieties]]''). It can be traced back to the old name of [[methanol#History|methanol]], "methylene" (from {{langx|grc|μέθυ}} ''{{Transliteration|grc|méthu}}'', 'wine' and {{lang|grc|ὕλη}} ''{{Transliteration|grc|húlē}}'',<ref>This name came through a Greek language error: ὕλη (''hȳlē'') means "wood" ("forest"), ξυλο- (''xylo''-) means "wood" (the substance)</ref> 'wood', 'forest'), which became shortened to "[[methyl group|methyl]]" in compound names, from which ''-yl'' was extracted.  Several reforms of chemical nomenclature eventually generalized the use of the suffix to other organic substituents. {{citation needed|date=January 2025}}

The use of the suffix is determined by the number of hydrogen atoms that the substituent replaces on a [[parent compound]] (and also, usually, on the substituent). According to the 1993 [[IUPAC]] recommendations:<ref>{{cite web|url=http://www.acdlabs.com/iupac/nomenclature/93/r93_271.htm|title=R-2.5 Substituent Prefix Names Derived from Parent Hydrides|work=A Guide to IUPAC Nomenclature of Organic Compounds (Recommendations 1993)|author=IUPAC|publisher=Blackwell Scientific Publications; Advanced Chemistry Development, Inc.|year=1997|orig-year=1993}}</ref>
* ''-yl'' means that one hydrogen is replaced.
* ''-ylidene'' means that two hydrogens are replaced by a [[double bond]] between parent and substituent.
* '''-'''''ylidyne'' means that three hydrogens are replaced by a [[triple bond]] between parent and substituent.

The suffix ''-ylid'''ine''''' is encountered sporadically, and appears to be a variant spelling of "-ylidene";<ref>The [[PubChem]] database lists 740,110 results for ''-ylidene'', of which 14 have synonyms where the suffix is replaced by ''-ylidine''. Another 4 results contain ''-ylidine'' without listing ''-ylidene'' as a synonym.</ref> it is not mentioned in the IUPAC guidelines.

For multiple bonds of the same type, which link the substituent to the parent group, the infixes ''-di-'', ''-tri-'', ''-tetra-'', etc., are used: ''-diyl'' (two single bonds), ''-triyl'' (three single bonds), ''-tetrayl'' (four single bonds), ''-diylidene'' (two double bonds).

For multiple bonds of different types, multiple suffixes are [[Concatenation|concatenated]]: '''-'''''ylylidene'' (one single and one double), ''-ylylidyne'' (one single and one triple), ''-diylylidene'' (two single and one double).

The parent compound name can be altered in two ways: {{citation needed|date=January 2025}}
* For many common compounds the substituent is linked at one end (the 1 position) and historically not numbered in the name. The IUPAC 2013 Rules<ref>{{Cite book|title=Nomenclature of Organic Chemistry. IUPAC Recommendations and Preferred Names 2013|date=2013|location=Cambridge, UK|publisher=Royal Society of Chemistry|others=Favre, Henri A.,, Powell, Warren H., 1934–, International Union of Pure and Applied Chemistry.|isbn=9781849733069|oclc=865143943}}</ref> however ''do'' require an explicit [[locant]] for most substituents in a [[preferred IUPAC name]]. The substituent name is modified by stripping ''-ane'' (see [[alkane]]) and adding the appropriate suffix. This is "recommended only for saturated acyclic and monocyclic hydrocarbon substituent groups and for the mononuclear parent [[hydride]]s of silicon, germanium, tin, lead, and boron". Thus, if there is a [[carboxylic acid]] called "''X''-ic acid", an [[Alcohol (chemistry)|alcohol]] ending "''X''-anol" (or "''X''-yl alcohol"), or an alkane called "''X''-ane", then "''X''-yl" typically denotes the same carbon chain lacking these groups but modified by attachment to some other parent molecule.
* The more general method omits only the terminal "e" of the substituent name, but requires explicit numbering of each ''yl'' prefix, even at position 1 (except for -ylidyne, which as a [[triple bond]] must terminate the substituent carbon chain). ''Pentan-1-yl'' is an example of a name by this method, and is synonymous with ''pentyl'' from the previous guideline.

Note that some popular terms such as "[[polyvinyl|vinyl]]" (when used to mean "polyvinyl") represent only a portion of the full chemical name. {{citation needed|date=January 2025}}