Functional group

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Benzyl acetate has an ester functional group (in red), an acetyl moiety (circled with green) and a benzyloxy moiety (circled with orange). Other divisions can be made.

In organic chemistry, functional groups are specific groups of atoms or bonds within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction(s) regardless of the size of the molecule it is a part of.[1][2] However, its relative reactivity can be modified by nearby functional groups.

The word moiety /ˈmɔɪəti/ is often used synonymously with "functional group" but, according to the IUPAC definition,[3] a moiety is a part of a molecule that may include either whole functional groups or parts of functional groups as substructures. For example, an ester (RCOOR') has an ester functional group (COOR) and is composed of an alkoxy moiety (-OR') and an acyl moiety (RCO-), or, equivalently, it may be divided into carboxylate (RCOO-) and alkyl (-R') moieties. This definition allows for a recursive nature, where moieties may contain functional groups which may contain moieties, etc. almost without limit (by definition, a functional group or moiety must have more than one atom, and the combination and structure must be of interest in itself). For example, methyl para-hydroxybenzoate contains a phenol functional group within the acyl moiety, which in turn is part of the paraben moiety.

Combining the names of functional groups with the names of the parent alkanes generates a powerful systematic nomenclature for naming organic compounds.

The atoms of functional groups are linked to each other and to the rest of the molecule by covalent bonds. When the group of covalently bound atoms bears a net charge, the group is referred to more properly as a polyatomic ion or a complex ion. Any subgroup of atoms of a compound also may be called a radical, and if a covalent bond is broken homolytically, the resulting fragment radicals are referred as free radicals.

The first carbon atom after the carbon that attaches to the functional group is called the alpha carbon; the second, beta carbon, the third, gamma carbon, etc. If there is another functional group at a carbon, it may be named with the Greek letter, e.g., the gamma-amine in gamma-aminobutanoic acid is on the third carbon of the carbon chain attached to the carboxylic acid group.

Synthetic chemistry[edit]

An aldol reaction of acetone with another ketone is not possible, because it would self-condense instead. The problem can be circumvented by replacing the ketone with the corresponding silyl enol ether in a Mukaiyama aldol addition. The silicon is then removed.

Organic reactions are facilitated and controlled by the functional groups of the reactants. In general, alkyls are unreactive and difficult to get to react selectively at the desired positions, with few exceptions. In contrast, unsaturated carbon functional groups, and carbon-oxygen and carbon-nitrogen functional groups have a more diverse array of reactions that are also selective. It may be necessary to create a functional group in the molecule to make it react. For example, to synthesize iso-octane (the 8-carbon ideal gasoline) from the unfunctionalized alkane isobutane (a 4-carbon gas), isobutane is first dehydrogenated into isobutene. This contains the alkene functional group and can now dimerize with another isobutene to give iso-octene, which is then catalytically hydrogenated to iso-octane using pressured hydrogen gas.


The International Union of Crystallography in its Crystallographic Information File dictionary defines "moiety" to represent discrete non-bonded components. Thus, Na
would contain 3 moieties (2 Na+ and one SO42-). The dictionary defines "chemical formula moiety": "Formula with each discrete bonded residue or ion shown as a separate moiety".


Functionalization is the addition of functional groups onto the surface of a material by chemical synthesis methods. The functional group added can be subjected to ordinary synthesis methods to attach virtually any kind of organic compound onto the surface.

Functionalization is employed for surface modification of industrial materials in order to achieve desired surface properties such as water repellent coatings for automobile windshields and non-biofouling, hydrophilic coatings for contact lenses. In addition, functional groups are used to covalently link functional molecules to the surface of chemical and biochemical devices such as microarrays and microelectromechanical systems.

Catalysts can be attached to a material that has been functionalized. For example, silica is functionalized with an alkyl silicone, wherein the alkyl contains an amine functional group. A ligand such as an EDTA fragment is synthesized onto the amine, and a metal cation is complexed into the EDTA fragment. The EDTA is not adsorbed onto the surface, but connected by a permanent chemical bond.

Functional groups are also used to covalently link molecules such as fluorescent dyes, nanoparticles, proteins, DNA, and other compounds of interest for a variety of applications such as sensing and basic chemical research.

Table of common functional groups[edit]

The following is a list of common functional groups. In the formulas, the symbols R and R' usually denote an attached hydrogen, or a hydrocarbon side chain of any length, but may sometimes refer to any group of atoms.


Functional groups, called hydrocarbyls, that contain only carbon and hydrogen, but vary in the number and order of double bonds. Each one differs in type (and scope) of reactivity.

Chemical classGroupFormulaStructural FormulaPrefixSuffixExample
AlkaneAlkylR(CH2)nHAlkylalkyl--aneEthan Keilstrich.svg
Benzene derivativePhenylRC6H5
Toluene derivativeBenzylRCH2C6H5
Benzylbenzyl-1-(substituent)tolueneBenzyl bromide
Benzyl bromide

There are also a large number of branched or ring alkanes that have specific names, e.g., tert-butyl, bornyl, cyclohexyl, etc.

Hydrocarbons may form charged structures: positively charged carbocations or negative carbanions. Carbocations are often named -um. Examples are tropylium and triphenylmethyl cations and the cyclopentadienyl anion.

Groups containing halogens[edit]

Haloalkanes are a class of molecule that is defined by a carbon–halogen bond. This bond can be relatively weak (in the case of an iodoalkane) or quite stable (as in the case of a fluoroalkane). In general, with the exception of fluorinated compounds, haloalkanes readily undergo nucleophilic substitution reactions or elimination reactions. The substitution on the carbon, the acidity of an adjacent proton, the solvent conditions, etc. all can influence the outcome of the reactivity.

Chemical classGroupFormulaStructural FormulaPrefixSuffixExample
haloalkanehaloRXHalide grouphalo-alkyl halideChloroethane-skeletal.svg
(Ethyl chloride)
fluoroalkanefluoroRFFluoro groupfluoro-alkyl fluorideFluoromethane.svg
(Methyl fluoride)
chloroalkanechloroRClChloro groupchloro-alkyl chlorideChloromethane
(Methyl chloride)
bromoalkanebromoRBrBromo groupbromo-alkyl bromideMethyl bromide.svg
(Methyl bromide)
iodoalkaneiodoRIIodo groupiodo-alkyl iodideIodomethane
(Methyl iodide)

Groups containing oxygen[edit]

Compounds that contain C-O bonds each possess differing reactivity based upon the location and hybridization of the C-O bond, owing to the electron-withdrawing effect of sp-hybridized oxygen (carbonyl groups) and the donating effects of sp2-hybridized oxygen (alcohol groups).

Chemical classGroupFormulaStructural FormulaPrefixSuffixExample
KetoneCarbonylRCOR'Ketone-oyl- (-COR')
oxo- (=O)
(Methyl ethyl ketone)
AldehydeAldehydeRCHOAldehydeformyl- (-COH)
oxo- (=O)
Acyl halideHaloformylRCOXAcyl halidecarbonofluoridoyl-
-oyl halideAcetyl chloride
Acetyl chloride
(Ethanoyl chloride)
CarbonateCarbonate esterROCOORCarbonate(alkoxycarbonyl)oxy-alkyl carbonatetriphosgene
(bis(trichloromethyl) carbonate)


carboxy--oateSodium acetate
Sodium acetate
(Sodium ethanoate)
Carboxylic acidCarboxylRCOOHCarboxylic acidcarboxy--oic acidAcetic acid
Acetic acid
(Ethanoic acid)
alkyl alkanoateEthyl butyrate
Ethyl butyrate
(Ethyl butanoate)
HydroperoxideHydroperoxyROOHHydroperoxyhydroperoxy-alkyl hydroperoxidetert-Butyl hydroperoxide
tert-Butyl hydroperoxide
PeroxidePeroxyROORPeroxyperoxy-alkyl peroxideDi-tert-butyl peroxide
Di-tert-butyl peroxide
EtherEtherROR'Etheralkoxy-alkyl etherDiethyl ether
Diethyl ether
HemiacetalHemiacetalRCH(OR')(OH)Hemiacetalalkoxy -ol-al alkyl hemiacetal
HemiketalHemiketalRC(ORʺ)(OH)R'Hemiketalalkoxy -ol-one alkyl hemiketal
AcetalAcetalRCH(OR')(OR")Acetaldialkoxy--al dialkyl acetal
Ketal (or Acetal)Ketal (or Acetal)RC(ORʺ)(OR‴)R'Ketaldialkoxy--one dialkyl ketal
HeterocycleMethylenedioxyPhOCOPhMethylenedioxy chemical structure.methylenedioxy--dioxole1,3-Benzodioxole.png
Orthocarbonate esterOrthocarbonate esterC(OR)(OR')(ORʺ)(OR″)tetralkoxy-tetraalkyl orthocarbonate

Groups containing nitrogen[edit]

Compounds that contain nitrogen in this category may contain C-O bonds, such as in the case of amides.

Chemical classGroupFormulaStructural FormulaPrefixSuffixExample
AminesPrimary amineRNH2Primary amineamino--aminemethylamine
Secondary amineR2NHSecondary amineamino--aminedimethylamine
Tertiary amineR3NTertiary amineamino--aminetrimethylamine
4° ammonium ionR4N+Quaternary ammonium cationammonio--ammoniumcholine
IminePrimary ketimineRC(=NH)R'Imineimino--imine
Secondary ketimineRC(=NR)R'Imineimino--imine
Primary aldimineRC(=NH)HImineimino--imineEthanimine
Secondary aldimineRC(=NR')HImineimino--imine
AzideAzideRN3Organoazideazido-alkyl azidePhenyl azide
Phenyl azide
Azo compoundAzo
RN2R'Azo.pnglazo--diazeneMethyl orange
Methyl orange
(p-dimethylamino-azobenzenesulfonic acid)
CyanatesCyanateROCNCyanatecyanato-alkyl cyanateMethyl cyanate
Methyl cyanate
IsocyanateRNCOIsocyanateisocyanato-alkyl isocyanateMethyl isocyanate
Methyl isocyanate
NitrateNitrateRONO2Nitratenitrooxy-, nitroxy-

alkyl nitrate

Amyl nitrate
Amyl nitrate
alkyl cyanide
(Phenyl cyanide)
alkyl isocyanide
Methyl isocyanide
Methyl isocyanide

alkyl nitrite

Amyl nitrite
Isoamyl nitrite
Nitro compoundNitroRNO2Nitronitro- Nitromethane
Nitroso compoundNitrosoRNONitrosonitroso- (Nitrosyl-) Nitrosobenzene
Pyridine derivativePyridylRC5H4N

4-pyridyl group
3-pyridyl group
2-pyridyl group





Groups containing sulfur[edit]

Compounds that contain sulfur exhibit unique chemistry due to their ability to form more bonds than oxygen, their lighter analogue on the periodic table. Substitutive nomenclature (marked as prefix in table) is preferred over functional class nomenclature (marked as suffix in table) for sulfides, disulfides, sulfoxides and sulfones.

Chemical classGroupFormulaStructural FormulaPrefixSuffixExample
SulfideRSR'Sulfide groupsubstituent sulfanyl-
Dimethyl sulfide

(Methylsulfanyl)methane (prefix) or
Dimethyl sulfide (suffix)
DisulfideDisulfideRSSR'Disulfidesubstituent disulfanyl-
Dimethyl disulfide

(Methyldisulfanyl)methane (prefix) or
Dimethyl disulfide (suffix)
SulfoxideSulfinylRSOR'Sulfinyl group-sulfinyl-
(Methanesulfinyl)methane (prefix) or
Dimethyl sulfoxide (suffix)
SulfoneSulfonylRSO2R'Sulfonyl group-sulfonyl-
di(substituentsulfoneDimethyl sulfone
(Methanesulfonyl)methane (prefix) or
Dimethyl sulfone (suffix)
Sulfinic acidSulfinoRSO2HSulfinic-acid-2D.pngsulfino-
-sulfinic acidHypotaurine
2-Aminoethanesulfinic acid
Sulfonic acidSulfoRSO3HSulfonyl groupsulfo-
-sulfonic acidBenzenesulfonic acid
Benzenesulfonic acid
substituent thiocyanatePhenyl thiocyanate
Phenyl thiocyanate
substituent isothiocyanateAllyl isothiocyanate
Allyl isothiocyanate

Groups containing phosphorus[edit]

Compounds that contain phosphorus exhibit unique chemistry due to their ability to form more bonds than nitrogen, their lighter analogues on the periodic table.

Chemical classGroupFormulaStructural FormulaPrefixSuffixExample
PhosphinoR3PA tertiary phosphinephosphanyl--phosphaneMethylpropylphosphane
Phosphonic acidPhosphonoRP(=O)(OH)2Phosphono groupphosphono-substituent phosphonic acidBenzylphosphonic acid
Benzylphosphonic acid
PhosphatePhosphateROP(=O)(OH)2Phosphate groupphosphonooxy-
O-phosphono- (phospho-)
substituent phosphateGlyceraldehyde 3-phosphate
Glyceraldehyde 3-phosphate (suffix)
O-Phosphonocholine (prefix)
di(substituent) hydrogen phosphate
phosphoric acid di(substituentester
O‑[(2‑Guanidinoethoxy)hydroxyphosphoryl]‑l‑serine (prefix)

Groups containing boron[edit]

Compounds containing boron exhibit unique chemistry due to their having partially filled octets and therefore acting as Lewis acids.

Chemical classGroupFormulaStructural FormulaPrefixSuffixExample
Boronic acidBoronoRB(OH)2Boronic-acid-2D.pngBorono-substituent
boronic acid
Phenylboronic acid
Phenylboronic acid
Boronic esterBoronateRB(OR)2Boronate-ester-2D.pngO-[bis(alkoxy)alkylboronyl]-substituent
boronic acid
di(substituent) ester
Borinic acidBorinoR2BOHBorinic-acid-2D.pngHydroxyborino-di(substituent)
borinic acid
Borinic esterBorinateR2BORBorinate-ester-2D.pngO-[alkoxydialkylboronyl]-di(substituent)
borinic acid
substituent ester
2-Aminoethoxydiphenyl borate
Diphenylborinic acid 2-aminoethyl ester
(2-Aminoethoxydiphenyl borate)

Names of radicals or moieties[edit]

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").[4]

Note that 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 methylene 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 single bonds).

There are some retained names, such as methylene for methanediyl, 1,x-phenylene for phenyl-1,x-diyl (where x is 2, 3, or 4),[5] carbyne for methylidyne, and trityl for triphenylmethyl.

Chemical classGroupFormulaStructural FormulaPrefixSuffixExample
Single bondR•Ylo-[6]-yl
Methyl group
Methyl radical
Double bondR: ?-ylidene
Triple bondR⫶ ?-ylidyne
Carboxylic acyl radicalAcylR−C(=O)• ?-oyl

Groups containing ions[edit]


See also[edit]


  1. ^ Compendium of Chemical Terminology (IUPAC "Gold Book")
  2. ^ March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7 
  3. ^ IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8 doi:10.1351/goldbook.M03968
  4. ^  Missing or empty |title= (help)
  5. ^ "R-2. 5 Substituent Prefix Names Derived from Parent Hydrides". IUPAC. 1993.  section P-56.2.1
  6. ^ "Revised Nomenclature for Radicals, Ions, Radical Ions and Related Species (IUPAC Recommendations 1993: RC-81.3. Multiple radical centers)". 
  7. ^ "Revised Nomenclature for Radicals, Ions, Radical Ions and Related Species (IUPAC Recommendations 1993)". 

External links[edit]