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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.
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.

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.

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 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
Alkane Alkyl R(CH2)nH
alkyl- -ane

Alkene Alkenyl R2C=CR2
alkenyl- -ene

Alkyne Alkynyl RC≡CR' alkynyl- -yne
Benzene derivative Phenyl RC6H5
phenyl- -benzene


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
haloalkane halo RX halo- alkyl halide

(Ethyl chloride)
fluoroalkane fluoro RF fluoro- alkyl fluoride

(Methyl fluoride)
chloroalkane chloro RCl chloro- alkyl chloride

(Methyl chloride)
bromoalkane bromo RBr bromo- alkyl bromide

(Methyl bromide)
iodoalkane iodo 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
hydroxy- -ol

Ketone Carbonyl RCOR'
-oyl- (-COR')
oxo- (=O)

(Methyl ethyl ketone)
Aldehyde Aldehyde RCHO
formyl- (-COH)
oxo- (=O)

Acyl halide Haloformyl RCOX
-oyl fluoride
-oyl chloride
-oyl bromide
-oyl iodide

Acetyl chloride
(Ethanoyl chloride)
Carbonate Carbonate ester ROCOOR'
(alkoxycarbonyl)oxy- alkyl carbonate

(bis(trichloromethyl) carbonate)
Carboxylate Carboxylate RCOO

carboxy- -oate

Sodium acetate
(Sodium ethanoate)
Carboxylic acid Carboxyl RCOOH
carboxy- -oic acid

Acetic acid
(Ethanoic acid)
Ester Carboalkoxy RCOOR'
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
Ether Ether ROR'
alkoxy- alkyl ether

Diethyl ether
Hemiacetal Hemiacetal R2CH(OR1)(OH)
alkoxy -ol -al alkyl hemiacetal
Hemiketal Hemiketal RC(ORʺ)(OH)R'
alkoxy -ol -one alkyl hemiketal
Acetal Acetal RCH(OR')(OR")
dialkoxy- -al dialkyl acetal
Ketal (or Acetal) Ketal (or Acetal) RC(OR")(OR‴)R'
dialkoxy- -one dialkyl ketal
Orthoester Orthoester RC(OR')(OR")(OR‴)
(if cyclic)
Methylenedioxy (–OCH2O–)

methylenedioxy- -dioxole

Orthocarbonate ester Orthocarbonate ester C(OR)(OR')(OR")(OR‴)
tetralkoxy- tetraalkyl orthocarbonate

Organic acid anhydride Carboxylic anhydride R1(CO)O(CO)R2

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
Amide Carboxamide RCONR'R"

Amidine Amidine RC(NR)NR2
-amidino -amidine


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
Imide Imide (RCO)2NR'
imido- -imide

Azide Azide RN3
azido- alkyl azide

Phenyl azide
Azo compound Azo
azo- -diazene

Methyl orange
(p-dimethylamino-azobenzenesulfonic acid)
Cyanates Cyanate ROCN
cyanato- alkyl cyanate

Methyl cyanate
Isocyanate RNCO
isocyanato- alkyl isocyanate

Methyl isocyanate
Nitrate Nitrate RONO2
nitrooxy-, nitroxy-

alkyl nitrate

Amyl nitrate
Nitrile Nitrile RCN cyano- alkanenitrile
alkyl cyanide

(Phenyl cyanide)
Isonitrile RNC isocyano- alkaneisonitrile
alkyl isocyanide

Methyl isocyanide
Nitrite Nitrosooxy RONO

alkyl nitrite

Isoamyl nitrite
Nitro compound Nitro RNO2

Nitroso compound Nitroso RNO
nitroso- (Nitrosyl-)  

Oxime Oxime RCH=NOH

Acetone oxime
(2-Propanone oxime)
Pyridine derivative Pyridyl RC5H4N





Carbamate ester Carbamate RO(C=O)NR2
(-carbamoyl)oxy- -carbamate

(Isopropyl (3-chlorophenyl)carbamate)

Groups containing sulfur

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

Sulfide RSR'
substituent sulfanyl-

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

(Methyldisulfanyl)methane (prefix) or
Dimethyl disulfide (suffix)
Sulfoxide Sulfinyl RSOR'

(Methanesulfinyl)methane (prefix) or
Dimethyl sulfoxide (suffix)
Sulfone Sulfonyl RSO2R'

(Methanesulfonyl)methane (prefix) or
Dimethyl sulfone (suffix)
Sulfinic acid Sulfino RSO2H
-sulfinic acid

2-Aminoethanesulfinic acid
Sulfonic acid Sulfo RSO3H
-sulfonic acid

Benzenesulfonic acid
Sulfonate ester Sulfo RSO3R'
R' R-sulfonate

Methyl trifluoromethanesulfonate or
Methoxysulfonyl trifluoromethane (prefix)
Thiocyanate Thiocyanate RSCN
substituent thiocyanate

Phenyl thiocyanate
Isothiocyanate RNCS
substituent isothiocyanate

Allyl isothiocyanate
Thioketone Carbonothioyl RCSR'

Thial Carbonothioyl RCSH
Thiocarboxylic acid Carbothioic S-acid RC=OSH
mercaptocarbonyl- -thioic S-acid

Thiobenzoic acid
(benzothioic S-acid)
Carbothioic O-acid RC=SOH
hydroxy(thiocarbonyl)- -thioic O-acid
Thioester Thiolester RC=OSR'

S-methyl thioacrylate
(S-methyl prop-2-enethioate)
Thionoester RC=SOR'
Dithiocarboxylic acid Carbodithioic acid RCS2H
dithiocarboxy- -dithioic acid

Dithiobenzoic acid
(Benzenecarbodithioic acid)
Dithiocarboxylic acid ester Carbodithio RC=SSR'

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
phosphanyl- -phosphane

Phosphonic acid Phosphono
phosphono- substituent phosphonic acid

Benzylphosphonic acid
Phosphate Phosphate
O-phosphono- (phospho-)
substituent phosphate

Glyceraldehyde 3-phosphate (suffix)

O-Phosphonocholine (prefix)
Phosphodiester Phosphate HOPO(OR)2
di(substituent) hydrogen phosphate
phosphoric acid di(substituentester
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 class Group Formula Structural Formula Prefix Suffix Example
Boronic acid Borono RB(OH)2
Borono- substituent
boronic acid

Phenylboronic acid
Boronic ester Boronate RB(OR)2
O-[bis(alkoxy)alkylboronyl]- substituent
boronic acid
di(substituent) ester
Borinic acid Borino R2BOH
Hydroxyborino- di(substituent)
borinic acid
Borinic ester Borinate R2BOR
O-[alkoxydialkylboronyl]- di(substituent)
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 class Group Formula Structural Formula Prefix Suffix Example
Single bond R• Ylo-[6] -yl
Methyl group
Methyl radical
Double bond R: ? -ylidene
Triple bond R⫶ ? -ylidyne
Carboxylic acyl radical Acyl R−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.