Substituent
In
The suffix -yl is used when naming
The phrases most-substituted and least-substituted are frequently used to describe or compare molecules that are products of a chemical reaction. In this terminology, methane is used as a reference of comparison. Using methane as a reference, for each hydrogen atom that is replaced or "substituted" by something else, the molecule can be said to be more highly substituted. For example:
- alkylsubstituents).
- Zaitsev's rulepredicts that the major reaction product is the alkene with the more highly substituted (more stable) double bond.
Nomenclature
The
The use of the suffix is determined by the number of hydrogen atoms that the substituent replaces on a
- -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 -ylidine is encountered sporadically, and appears to be a variant spelling of "-ylidene";[6] 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 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:
- 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[7] 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 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 "
Methane substituents
According to the above rules, a carbon atom in a molecule, considered as a substituent, has the following names depending on the number of hydrogens bound to it, and the type of bonds formed with the remainder of the molecule:
| CH 4 |
methane | no bonds |
| −CH 3 |
methyl group or methanyl | one single bond to a non-hydrogen atom |
| =CH 2 |
methylene group or methanylidene or methylidene | one double bond |
| −CH 2− |
methylene bridge or methanediyl or methdiyl | two single bonds |
| ≡CH | methanylidyne group or methylidyne | one triple bond |
| =CH− | methine group or methanylylidene or methylylidene | one single bond and one double bond |
| >CH− | methanetriyl group or methtriyl | three single bonds |
| ≡C− | methanylylidyne group or methylylidyne | one triple bond and one single bond |
| =C= | methanediylidene group or methdiylidene | two double bonds |
| >C= | methanediylylidene group or methdiylylidene | two single bonds and one double bond |
| >C< | methanetetrayl group or methtetrayl | four single bonds |
Notation
In a chemical
The symbol X is often used to denote electronegative substituents such as the
Statistical distribution
One
See also
- Functional groups are a subset of substituents
References
- ^ "Definition of SUBSTITUENT". www.merriam-webster.com. Retrieved 4 June 2022.
- ISBN 978-0-07-145920-4.
- . This distinguishes a pendant group as neither oligomeric nor polymeric, whereas a pendant chain must be oligomeric or polymeric.
- ^ This name came through a Greek language error: ὕλη (hȳlē) means "wood" ("forest"), ξυλο- (xylo-) means "wood" (the substance)
- ^ IUPAC (1997) [1993]. "R-2.5 Substituent Prefix Names Derived from Parent Hydrides". A Guide to IUPAC Nomenclature of Organic Compounds (Recommendations 1993). Blackwell Scientific Publications; Advanced Chemistry Development, Inc.
- ^ 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.
- )
- ^ See:
- Charles Gerhardt, Précis de chimie organique (Summary of organic chemistry), vol. 1 (Paris, France: Fortin et Masson, 1844), page 29. From page 29: "En désignant, par conséquent, les éléments combustibles par R, sans tenir comptes des proportions atomiques de carbone et d'hydrogène, on peut exprimer d'une manière générale: Par R. — Les hydrogènes carbonés." (Consequently, by designating combustible components by R, without considering the atomic proportions of carbon and hydrogen, one can express in a general way: By R — hydrocarbons.)
- William B. Jensen (2010) "Ask the Historian: Why is R Used for Hydrocarbon Substituents?," Journal of Chemical Education, 87: 360–361. Available at: University of Cincinnati.
- .
- ^ The first use of the letter X to denote univalent electronegative groups appeared in:
- Stanislao Cannizzaro (1858) "Sunto di un corso di filosofia chimica, fatto nella R. Universita di Genova" (Sketch of a course of chemical philosophy, offered at the Royal University of Genoa), Il Nouvo Cimento (The New Experiment), 7 : 321–366. From page 355: " … X indica tutto ciò che vi è nella molecola, oltre l'idrogeno metallico … " ( … X stands for all that is in the molecule, apart from metallic hydrogen … ).
- PMID 12653499.