Functional group

In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest of the molecule's composition.[1][2] This enables systematic prediction of chemical reactions and behavior of chemical compounds and the design of chemical synthesis. The reactivity of a functional group can be modified by other functional groups nearby. Functional group interconversion can be used in retrosynthetic analysis to plan organic synthesis.

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

A functional group is a group of atoms in a molecule with distinctive chemical properties, regardless of the other atoms in the molecule. The atoms in a functional group are linked to each other and to the rest of the molecule by covalent bonds. For repeating units of polymers, functional groups attach to their nonpolar core of carbon atoms and thus add chemical character to carbon chains. Functional groups can also be charged, e.g. in carboxylate salts (–COO), which turns the molecule into a polyatomic ion or a complex ion. Functional groups binding to a central atom in a coordination complex are called ligands. Complexation and solvation are also caused by specific interactions of functional groups. In the common rule of thumb "like dissolves like", it is the shared or mutually well-interacting functional groups which give rise to solubility. For example, sugar dissolves in water because both share the hydroxyl functional group (–OH) and hydroxyls interact strongly with each other. Plus, when functional groups are more electronegative than atoms they attach to, the functional groups will become polar, and the otherwise nonpolar molecules containing these functional groups become polar and so become soluble in some aqueous environment.

Combining the names of functional groups with the names of the parent alkanes generates what is termed a systematic nomenclature for naming organic compounds. In traditional nomenclature, 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-aminobutyric acid is on the third carbon of the carbon chain attached to the carboxylic acid group. IUPAC conventions call for numeric labeling of the position, e.g. 4-aminobutanoic acid. In traditional names various qualifiers are used to label isomers, for example, isopropanol (IUPAC name: propan-2-ol) is an isomer of n-propanol (propan-1-ol). The term moiety has some overlap with the term "functional group". However, a moiety is an entire "half" of a molecule, which can be not only a single functional group, but also a larger unit consisting of multiple functional groups. For example, an "aryl moiety" may be any group containing an aromatic ring, regardless of how many functional groups the said aryl has.

Table of common functional groups

The following is a list of common functional groups.[3] 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.


Hydrocarbons are a class of molecule that is defined by 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 class Group Formula Structural Formula Prefix Suffix Example
AlkaneAlkyl R(CH2)nH alkyl--ane
AlkeneAlkenyl R2C=CR2 alkenyl--ene
AlkyneAlkynyl RC≡CR' alkynyl--yne
Benzene derivative Phenyl RC6H5

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 halogen

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
haloalkanehalo RX halo-alkyl halide
(Ethyl chloride)
fluoroalkanefluoro RF fluoro-alkyl fluoride
(Methyl fluoride)
chloroalkanechloro RCl chloro-alkyl chloride
(Methyl chloride)
bromoalkanebromo RBr bromo-alkyl bromide
(Methyl bromide)
iodoalkaneiodo RI iodo-alkyl iodide
(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
Carbonyl functionCarbonyl CO
KetoneKetone RCOR' -oyl- (-COR')
oxo- (=O)
(Methyl ethyl ketone)
AldehydeAldehyde RCHO formyl- (-COH)
oxo- (=O)
Acyl halideHaloformyl RCOX carbonofluoridoyl-
-oyl fluoride
-oyl chloride
-oyl bromide
-oyl iodide

Acetyl chloride
(Ethanoyl chloride)
Carbonate Carbonate ester ROCOOR' (alkoxycarbonyl)oxy- alkyl carbonate
(bis(trichloromethyl) carbonate)
Carboxylate CarboxylateRCOO

Sodium acetate
(Sodium ethanoate)
Carboxylic acid CarboxylRCOOH carboxy--oic acid
Acetic acid
(Ethanoic acid)
EsterCarboalkoxy RCOOR' alkanoyloxy-
alkyl alkanoate
Ethyl butyrate
(Ethyl butanoate)
Hydroperoxide Hydroperoxy ROOH hydroperoxy- alkyl hydroperoxide
tert-Butyl hydroperoxide
Peroxide Peroxy ROOR' peroxy- alkyl peroxide
Di-tert-butyl peroxide
EtherEther ROR'
alkoxy- alkyl ether
Diethyl ether
HemiacetalHemiacetal R2CH(OR1)(OH) alkoxy -ol -al alkyl hemiacetal
HemiketalHemiketal RC(ORʺ)(OH)R' alkoxy -ol -one alkyl hemiketal
AcetalAcetal RCH(OR')(OR") dialkoxy- -al dialkyl acetal
Ketal (or Acetal)Ketal (or Acetal) RC(OR")(OR‴)R' dialkoxy- -one dialkyl ketal
OrthoesterOrthoester RC(OR')(OR")(OR‴) trialkoxy-
(if cyclic)
Methylenedioxy (–OCH2O–)

methylenedioxy- -dioxole
Orthocarbonate esterOrthocarbonate ester C(OR)(OR')(OR")(OR‴) tetralkoxy- tetraalkyl orthocarbonate
Organic acid anhydrideCarboxylic anhydride R1(CO)O(CO)R2 anhydride
Butyric anhydride

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
AmideCarboxamide RCONR'R" carboxamido-
Amidine Amidine RC(NR)NR2 amidino- -amidine acetamidine


Amines Primary amine RNH2 amino--amine
Secondary amine R'R"NH amino--amine
Tertiary amine R3N amino--amine
4° ammonium ion R4N+ ammonio--ammonium
Imine Primary ketimine RC(=NH)R' imino--imine
Secondary ketimine imino--imine
Primary aldimine RC(=NH)H imino--imine
Secondary aldimine RC(=NR')H imino--imine
ImideImide (RCO)2NR' imido- -imide
Azide Azide RN3 azido-alkyl azide
Phenyl azide
Azo compound Azo
RN2R' azo--diazene
Methyl orange
(p-dimethylamino-azobenzenesulfonic acid)
Cyanates CyanateROCN cyanato- alkyl cyanate
Methyl cyanate
IsocyanateRNCO isocyanato- alkyl isocyanate
Methyl isocyanate
NitrateNitrate RONO2 nitrooxy-, nitroxy-

alkyl nitrate

Amyl nitrate
Nitrile Nitrile RCN cyano- alkanenitrile
alkyl cyanide

(Phenyl cyanide)
IsonitrileRNC isocyano- alkaneisonitrile
alkyl isocyanide

Methyl isocyanide
NitriteNitrosooxy RONO nitrosooxy-

alkyl nitrite

Isoamyl nitrite
Nitro compound Nitro RNO2 nitro- 
Nitroso compound NitrosoRNO nitroso- (Nitrosyl-) 
Oxime OximeRCH=NOH  Oxime
Acetone oxime
(2-Propanone oxime)
Pyridine derivative Pyridyl RC5H4N




Carbamate ester CarbamateRO(C=O)NR2 (-carbamoyl)oxy--carbamate
(Isopropyl (3-chlorophenyl)carbamate)

Groups containing sulfur

Compounds that contain sulfur exhibit unique chemistry due to sulfur's ability to form more bonds than oxygen, its 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 sulfanyl-
Sulfide RSR' substituent sulfanyl-
di(substituent) sulfide

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

(Methyldisulfanyl)methane (prefix) or
Dimethyl disulfide (suffix)
Sulfoxide Sulfinyl RSOR' -sulfinyl-
di(substituent) sulfoxide
(Methanesulfinyl)methane (prefix) or
Dimethyl sulfoxide (suffix)
Sulfone Sulfonyl RSO2R' -sulfonyl-
di(substituent) sulfone
(Methanesulfonyl)methane (prefix) or
Dimethyl sulfone (suffix)
Sulfinic acidSulfino RSO2H sulfino-
-sulfinic acid
2-Aminoethanesulfinic acid
Sulfonic acidSulfo RSO3H sulfo-
-sulfonic acid
Benzenesulfonic acid
Sulfonate esterSulfo RSO3R' (-sulfonyl)oxy-
R' R-sulfonate
Methyl trifluoromethanesulfonate or
Methoxysulfonyl trifluoromethane (prefix)
Thiocyanate ThiocyanateRSCN thiocyanato-
substituent thiocyanate
Phenyl thiocyanate
IsothiocyanateRNCS isothiocyanato-
substituent isothiocyanate
Allyl isothiocyanate
Thioketone Carbonothioyl RCSR' -thioyl-
Thial Carbonothioyl RCSH methanethioyl-
Thiocarboxylic acid Carbothioic S-acid RC=OSH
Thioic S-acid
mercaptocarbonyl- -thioic S-acid
Thiobenzoic acid
(benzothioic S-acid)
Carbothioic O-acid RC=SOH
Thioic O-acid
hydroxy(thiocarbonyl)- -thioic O-acid
Thioester Thiolester RC=OSR' S-alkyl-alkane-thioate
S-methyl thioacrylate
(S-methyl prop-2-enethioate)
Thionoester RC=SOR' O-alkyl-alkane-thioate
Dithiocarboxylic acid Carbodithioic acid RCS2H
Dithiocarboxylic acid
dithiocarboxy- -dithioic acid
Dithiobenzoic acid
(Benzenecarbodithioic acid)
Dithiocarboxylic acid ester Carbodithio RC=SSR' -dithioate

Groups containing phosphorus

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

Chemical class Group Formula Structural Formula Prefix Suffix Example
Phosphino R3P phosphanyl--phosphane
Phosphonic acid Phosphono phosphono- substituent phosphonic acid
Benzylphosphonic acid
Phosphate Phosphate phosphonooxy-
O-phosphono- (phospho-)
substituent phosphate
Glyceraldehyde 3-phosphate (suffix)

O-Phosphonocholine (prefix)
Phosphodiester Phosphate HOPO(OR)2 [(alkoxy)hydroxyphosphoryl]oxy-
di(substituent) hydrogen phosphate
phosphoric acid di(substituent) ester
O‑[(2‑Guanidinoethoxy)hydroxyphosphoryl]‑l‑serine (prefix)

Groups containing boron

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)2
boronic acid
Boronic esterBoronateRB(OR)2
boronic acid
di(substituent) ester
Borinic acidBorinoR2BOH
borinic acid
Borinic esterBorinateR2BOR
borinic acid
substituent ester

Diphenylborinic acid 2-aminoethyl ester
(2-Aminoethoxydiphenyl borate)

Groups containing metals

Chemical Class Structural Formula Prefix Suffix Example
Alkyllithium RLi (tri/di)alkyl- -lithium


Alkylmagnesium halide RMgX (X=Cl, Br, I)[note 1] -magnesium halide

methylmagnesium chloride

Alkylaluminium Al2R6 -aluminium


Silyl ether R3SiOR -silyl ether

trimethylsilyl triflate

note 1 Fluorine is too electronegative to be bonded to magnesium; it becomes an ionic salt instead.

Names of radicals or moieties

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]

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 double 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
Double bondR: ?-ylidene
Triple bondR⫶ ?-ylidyne
Carboxylic acyl radicalAcylR−C(=O)• ?-oyl

See also


  1. Compendium of Chemical Terminology (IUPAC "Gold Book") functional group
  2. March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7
  3. Brown, Theodore (2002). Chemistry: the central science. Upper Saddle River, NJ: Prentice Hall. p. 1001. ISBN 0130669970.
  4. Moss, G. P.; W.H. Powell. "RC-81.1.1. Monovalent radical centers in saturated acyclic and monocyclic hydrocarbons, and the mononuclear EH4 parent hydrides of the carbon family". IUPAC Recommendations 1993. Department of Chemistry, Queen Mary University of London. Archived from the original on 9 February 2015. Retrieved 25 February 2015.
  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)". Archived from the original on 2017-06-11. Retrieved 2014-12-02.
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