Substituent - Nomenclature

Nomenclature

The suffix yl is used in Organic chemistry to form names of radicals, either separate or chemically bonded parts of molecules.It can be traced back to the word methylene (methy = "wine" + hȳlē = wood), evolving through the gradual regularization of chemical names to its current meaning.

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 1993 IUPAC guidelines:

• -yl means that one hydrogen is replaced.
• -ylidene means that two hydrogens are replaced by a double bond between parent and substituent. The term "-ylidine" is encountered sporadically, and is often used synonymously with -ylidene.The spelling "-ylidine" seems to be a rare usage in some contexts, but it appears in manufacturer's publications about Sunitinib PubChem indexes 740,110 results for "-ylidene", of which 14 use synonyms that replace the suffix freely with "-ylidine".An additional four compound entries contain "-ylidine" without listing "-ylidene" as a synonym. The word "-ylidine" is not in IUPAC guidelines.
• -ylidyne means that three hydrogens are replaced by a triple bond between parent and substituent.For multiple bonds of the same type, which link the substituent to the parent group, the prefixes 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 bond types, multiple suffixes are added:
  • -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 different ways.

• For many common compounds the substituent is linked at one end (the 1 position), which is therefore not explicitly numbered in the formula.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 hydrides of silicon, germanium, tin, lead, and boron". Thus, if there is a carboxylic acid called "X-ic acid", an 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 "vinyl" (when used to mean "polyvinyl") represent only a portion of the full chemical name.