Functional group

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, functional groups are specific groups (moieties) 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 other functional groups nearby. 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.

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

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.


Functional groups, called hydrocarbyl, 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 Formulae 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 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 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 carbonofluoridoyl-
-oyl halide
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 Ester RCOOR' alkanoyloxy-
alkyl alkanoate
Ethyl butyrate
(Ethyl butanoate)
Methoxy Methoxy ROCH3 methoxy-
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 RCH(OR')(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(ORʺ)(OR)R' dialkoxy- -one dialkyl ketal
Orthoester Orthoester RC(OR')(ORʺ)(OR) trialkoxy-
Heterocycle Methylenedioxy PhOCOPh methylenedioxy- -dioxole
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 carboxamido-
Amines Primary amine RNH2 amino- -amine
Secondary amine R2NH 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
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





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 sulfanyl-
Sulfide RSR' substituent sulfanyl-
di(substituent) sulfide

(Methylsulfanyl)methane (prefix) or
Dimethyl sulfide (suffix)
Disulfide Disulfide 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 acid Sulfino RSO2H sulfino-
-sulfinic acid
2-Aminoethanesulfinic acid
Sulfonic acid Sulfo RSO3H sulfo-
-sulfonic acid
Benzenesulfonic acid
Thiocyanate Thiocyanate RSCN thiocyanato-
substituent thiocyanate
Phenyl thiocyanate
Isothiocyanate RNCS isothiocyanato-
substituent isothiocyanate
Allyl isothiocyanate
Thione Carbonothioyl RCSR' -thioyl-
Thial Carbonothioyl RCSH methanethioyl-
carbodithioic acid

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 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 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)

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]

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 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")
  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)".

External links

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