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.

Example functional groups of benzyl acetate:
  Ester group
  Acetyl group
  Benzyloxy group

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
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 Ketone RCOR'   -oyl- (-COR')
oxo- (=O)
(Methyl ethyl ketone)
Aldehyde Aldehyde RCHO   formyl- (-COH)
oxo- (=O)
Acyl halide Haloformyl 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 Carboxylate RCOO

carboxylato- -oate  
Sodium acetate
(Sodium ethanoate)
Carboxylic acid Carboxyl RCOOH   carboxy- -oic acid  
Acetic acid
(Ethanoic acid)
Ester Carboalkoxy 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
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‴)   trialkoxy-
(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   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
Amide Carboxamide 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  
Hydrazone R'R"CN2H2
hydrazino- -hydrazine
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
RN2R'   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   nitrosooxy-

alkyl nitrite

Isoamyl nitrite
Nitro compound Nitro RNO2   nitro-    
Nitroso compound Nitroso RNO   nitroso- (Nitrosyl-)    
Oxime Oxime RCH=NOH     Oxime  
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 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-

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

(Methyldisulfanyl)methane (prefix) or
Dimethyl disulfide (suffix)
Sulfoxide Sulfinyl RSOR'   -sulfinyl-
(Methanesulfinyl)methane (prefix) or
Dimethyl sulfoxide (suffix)
Sulfone Sulfonyl RSO2R'   -sulfonyl-
(Methanesulfonyl)methane (prefix) or
Dimethyl sulfone (suffix)
Sulfinic acid Sulfino RSO2H   sulfino-
-sulfinic acid  
2-Aminoethanesulfinic acid
Sulfonic acid Sulfo RSO3H   sulfo-
-sulfonic acid  
Benzenesulfonic acid
Sulfonate ester Sulfo RSO3R'   (-sulfonyl)oxy-
R' R-sulfonate  
Methyl trifluoromethanesulfonate or
Methoxysulfonyl trifluoromethane (prefix)
Thiocyanate Thiocyanate RSCN   thiocyanato-
substituent thiocyanate  
Phenyl thiocyanate
Isothiocyanate RNCS   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(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
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 methylidene 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
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 Archived 2019-05-16 at the Wayback Machine
  2. ^ March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 3rd edition, New York: Wiley, ISBN 9780471854722, OCLC 642506595
  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. Archived from the original on 2019-03-22. Retrieved 2018-12-15. 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.
  • IUPAC Blue Book (organic nomenclature)
  • "IUPAC ligand abbreviations" (PDF). IUPAC. 2 April 2004. Archived from the original (PDF) on 27 September 2007. Retrieved 25 February 2015.
  • Functional group video