Functional group

Functional group
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 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 (pronounced /ˈmɔɪəti/) is often used synonymously to "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 a 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. Each moiety may contain additional functional groups, for example, methyl para-hydroxybenzoate contains a phenol functional group within the acyl 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

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, Na2SO4 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

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 π bonds. Each one differs in type (and scope) of reactivity.

Chemical class Group Formula Structural Formula Prefix Suffix Example
Alkane Alkyl RH Alkyl alkyl- -ane methane
Alkene Alkenyl R2C=CR2 Alkene alkenyl- -ene ethylene
Alkyne Alkynyl RC≡CR' Alkyne alkynyl- -yne acetylene
Benzene derivative Phenyl RC6H5
Phenyl phenyl- -benzene Cumene
Toluene derivative Benzyl RCH2C6H5
Benzyl benzyl- 1-(substituent)toluene Benzyl 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

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 class Group Formula Structural Formula Prefix Suffix Example
haloalkane halo RX Halide group halo- alkyl halide Chloroethane
(Ethyl chloride)
fluoroalkane fluoro RF Fluoro group fluoro- alkyl fluoride Fluoromethane
(Methyl fluoride)
chloroalkane chloro RCl Chloro group chloro- alkyl chloride Chloromethane
(Methyl chloride)
bromoalkane bromo RBr Bromo group bromo- alkyl bromide Bromomethane
(Methyl bromide)
iodoalkane iodo RI Iodo group iodo- alkyl iodide Iodomethane
(Methyl iodide)

Groups containing oxygen

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 class Group Formula Structural Formula Prefix Suffix Example
Alcohol Hydroxyl ROH Hydroxyl hydroxy- -ol methanol
Ketone Carbonyl RCOR' Ketone -oyl- (-COR')
oxo- (=O)
-one Butanone
(Methyl ethyl ketone)
Aldehyde Aldehyde RCHO Aldehyde formyl- (-COH)
oxo- (=O)
-al acetaldehyde
Acyl halide Haloformyl RCOX Acyl halide carbonofluoridoyl-
-oyl halide Acetyl chloride
Acetyl chloride
(Ethanoyl chloride)
Carbonate Carbonate ester ROCOOR Carbonate (alkoxycarbonyl)oxy- alkyl carbonate triphosgene
(Di(trichloromethyl) carbonate)
Carboxylate Carboxylate RCOO Carboxylate


carboxy- -oate Sodium acetate
Sodium acetate
(Sodium ethanoate)
Carboxylic acid Carboxyl RCOOH Carboxylic acid carboxy- -oic acid Acetic acid
Acetic acid
(Ethanoic acid)
Ester Ester RCOOR' Ester alkanoyloxy-
alkyl alkanoate Ethyl butyrate
Ethyl butyrate
(Ethyl butanoate)
Hydroperoxide Hydroperoxy ROOH Hydroperoxy hydroperoxy- alkyl hydroperoxide Methyl ethyl ketone peroxide
Methyl ethyl ketone peroxide
Peroxide Peroxy ROOR Peroxy peroxy- alkyl peroxide Di-tert-butyl peroxide
Di-tert-butyl peroxide
Ether Ether ROR' Ether alkoxy- alkyl ether Diethyl ether
Diethyl ether
Hemiacetal Hemiacetal RCH(OR')(OH) Hemiacetal alkoxy -ol -al alkyl hemiacetal
Hemiketal Hemiketal RC(ORʺ)(OH)R' Hemiketal alkoxy -ol -one alkyl hemiketal
Acetal Acetal RCH(OR')(OR") Acetal dialkoxy- -al dialkyl acetal
Ketal (or Acetal) Ketal (or Acetal) RC(ORʺ)(OR‴)R' Ketal dialkoxy- -one dialkyl ketal
Orthoester Orthoester RC(OR')(ORʺ)(OR‴) Orthoester trialkoxy-
Orthocarbonate ester Orthocarbonate ester C(OR)(OR')(ORʺ)(OR″) tetralkoxy- tetraalkyl orthocarbonate

Groups containing nitrogen

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

Chemical class Group Formula Structural Formula Prefix Suffix Example
Amide Carboxamide RCONR2 Amide carboxamido-
-amide acetamide
Amines Primary amine RNH2 Primary amine amino- -amine methylamine
Secondary amine R2NH Secondary amine amino- -amine dimethylamine
Tertiary amine R3N Tertiary amine amino- -amine trimethylamine
4° ammonium ion R4N+ Quaternary ammonium cation ammonio- -ammonium choline
Imine Primary ketimine RC(=NH)R' Imine imino- -imine
Secondary ketimine RC(=NR)R' Imine imino- -imine
Primary aldimine RC(=NH)H Imine imino- -imine
Secondary aldimine RC(=NR')H Imine imino- -imine
Imide Imide (RCO)2NR' Imide imido- -imide
Azide Azide RN3 Organoazide azido- alkyl azide Phenyl azide
Phenyl azide
Azo compound Azo
RN2R' Azo.pngl azo- -diazene Methyl orange
Methyl orange
(p-dimethylamino-azobenzenesulfonic acid)
Cyanates Cyanate ROCN Cyanate cyanato- alkyl cyanate Methyl cyanate
Methyl cyanate
Isocyanate RNCO Isocyanate isocyanato- alkyl isocyanate Methyl isocyanate
Methyl isocyanate
Nitrate Nitrate RONO2 Nitrate nitrooxy-, nitroxy-

alkyl nitrate

Amyl nitrate
Amyl nitrate
Nitrile Nitrile RCN Nitrile cyano- alkanenitrile
alkyl cyanide
(Phenyl cyanide)
Isonitrile RNC Isocyanide isocyano- alkaneisonitrile
alkyl isocyanide
Methyl isocyanide
Methyl isocyanide
Nitrite Nitrosooxy RONO Nitrite nitrosooxy-

alkyl nitrite

Amyl nitrite
Isoamyl nitrite
Nitro compound Nitro RNO2 Nitro nitro-   Nitromethane
Nitroso compound Nitroso RNO Nitroso nitroso-   Nitrosobenzene
Pyridine derivative Pyridyl RC5H4N

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




-pyridine Nicotine

Groups containing sulphur

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 class Group Formula Structural Formula Prefix Suffix Example
Thiol Sulfhydryl RSH Sulfhydryl sulfanyl-
-thiol Ethanethiol
Sulfide RSR' Sulfide group substituent sulfanyl-
Dimethyl sulfide

(Methylsulfanyl)methane (prefix) or
Dimethyl sulfide (suffix)
Disulfide Disulfide RSSR' Disulfide substituent disulfanyl-
Dimethyl disulfide

(Methyldisulfanyl)methane (prefix) or
Dimethyl disulfide (suffix)
Sulfoxide Sulfinyl RSOR' Sulfinyl group -sulfinyl-
di(substituentsulfoxide DMSO
(Methanesulfinyl)methane (prefix) or
Dimethyl sulfoxide (suffix)
Sulfone Sulfonyl RSO2R' Sulfonyl group -sulfonyl-
di(substituentsulfone Dimethyl sulfone
(Methanesulfonyl)methane (prefix) or
Dimethyl sulfone (suffix)
Sulfinic acid Sulfino RSO2H Sulfinic-acid-2D.png sulfino-
-sulfinic acid Hypotaurine
2-Aminoethanesulfinic acid
Sulfonic acid Sulfo RSO3H Sulfonyl group sulfo-
-sulfonic acid Benzenesulfonic acid
Benzenesulfonic acid
Thiocyanate Thiocyanate RSCN Thiocyanate thiocyanato-
substituent thiocyanate Phenyl thiocyanate
Phenyl thiocyanate
Isothiocyanate RNCS Isothiocyanate isothiocyanato-
substituent isothiocyanate Allyl isothiocyanate
Allyl isothiocyanate
Thione Carbonothioyl RCSR' Thione -thioyl-
-thione Diphenylmethanethione
Thial Carbonothioyl RCSH Thial methanethioyl-

Groups containing phosphorus

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 class Group Formula Structural Formula Prefix Suffix Example
Phosphino R3P A tertiary phosphine phosphanyl- -phosphane Methylpropylphosphane
Phosphonic acid Phosphono RP(=O)(OH)2 Phosphono group phosphono- substituent phosphonic acid Benzylphosphonic acid
Benzylphosphonic acid
Phosphate Phosphate ROP(=O)(OH)2 Phosphate group phosphonooxy-
O-phosphono- (phospho-)
substituent phosphate Glyceraldehyde 3-phosphate
Glyceraldehyde 3-phosphate (suffix)
O-Phosphonocholine (prefix)
Phosphodiester Phosphate HOPO(OR)2 Phosphodiester [(alkoxy)hydroxyphosphoryl]oxy-
di(substituent) hydrogen phosphate
phosphoric acid di(substituentester
O‑[(2‑Guanidinoethoxy)hydroxyphosphoryl]‑L‑serine (prefix)

See also

  • For a list of all functional groups: Category:Functional groups


  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

External links

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