Functional group

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In organic chemistry , a functional group (also a characteristic group ) is the group of atoms in a compound that significantly determines the material properties and the reaction behavior of the compound. A compound can also carry several functional groups with different properties. Compounds that have the same functional groups but different alkyl or aryl radicals are grouped into substance classes due to their similar properties .

Functional groups are divided into functional groups with heteroatoms (mostly O, N, S, P, halogens) and those without heteroatoms (e.g. C = C double bonds , C≡C triple bonds or aromatics ) based on the atoms involved . Even if the latter are sometimes not viewed as “fully-fledged” functional groups, but only as structural building blocks, they still show a special and typical reaction behavior that justifies the designation functional group and the respective grouping into substance classes.

In the case of inorganic or organometallic compounds, simple alkyl or aryl groups are also regarded as functional groups. All organic side chains and functional groups are then summarized under the general name organyl group .

There are abbreviations for functional groups to simplify the writing in structural formulas and texts, which are listed in the list of abbreviations in organic chemistry .


According to the definition, a functional group usually has a considerable influence on the chemical and physical properties of the starting compound it contains. The type of influence is demonstrated using the example of the alkane n -butane and three of its structural derivatives with the same number of carbon atoms:

Structural descendant
with the same number of carbon atoms
connection Semi-structural formula properties
Output compound n -Butane H 3 C-CH 2 -CH 2 -CH 3 gaseous
Carboxy compound Butanoic acid , also butyric acid H 3 C-CH 2 -CH 2 -COOH liquid, foul smelling, reacts sour
Amino compound Butan-2-amine , also 2-butylamine H 3 C-CH (NH 2 ) -CH 2 -CH 3 liquid, foul smelling, has a basic reaction
Carboxy and amino compound 4-aminobutyric acid, also 4-aminobutyric acid
or γ-aminobutyric acid (GABA)
H 2 N-CH 2 -CH 2 -CH 2 -COOH solid, exists in aqueous solution as a
zwitterion H 3 N + –CH 2 –CH 2 –CH 2 –COO -

Different functional groups and their nomenclature

Basically, the substitutive nomenclature , which is described below, should be used to name substances. According to this nomenclature, the functional group is either a prefix ( prefix ) or as a suffix ( suffix included) on behalf of the total composition.

See also: nomenclature

Functional groups (in order of decreasing priority)

Either prefixes or suffixes are used to designate these groups in a connection. The highest-ranking group is used as an ending and all others, in alphabetical order, as prefixes. The different classes of compounds are listed in the following table in order of decreasing priority.

Sometimes there are different names depending on whether the specified carbon atom represents part of the parent system (see keyword nomenclature ) (representation: RC XYZ ) or not (representation: R -CXYZ ). As usual in chemistry, the letter R stands for an organic residue . The placeholder X stands for halides .

Semi-structural formula Structural formula Substance class Prefix Ending (suffix) Examples
R or R : radical Ylo- -yl
z. B. Cl • or triplet carbene
Cations -ium
z. B. Cationic surfactants ,
General structure of the monocarboxylic acid with the carboxy function highlighted in blue
Carboxylic acids Carboxy
z. B. formic acid , acetic acid ,
butyric acid , amino acids
General structure of the peroxycarboxylic acid with the peroxycarboxyl residue marked in blue
Peroxycarboxylic acids Hydroperoxycarbonyl
acid -peroxy .... acid
z. B. peroxyacetic acid


General structures of thiocarboxylic acids
Thiocarboxylic acids Hydroxy (thiocarbonyl) -
(dithiocarboxy) -
-carbothio- O acid

thio O acid
-carbothio- S acid

thio S acid
R- SO 2 -OH
General structure of sulfonic acid
Sulfonic acids Sulfo- sulfonic acid z. B. benzenesulfonic acid
General structure of sulfinic acid
Sulfinic acids Sulfino sulfinic acid
R 1 - CO-S -R 2
General structure of the thiolester
Thiolester R 1 oyl -thio- S -R 2 yl -R 1 thioate
General structure of sulfenic acid
Sulfenic acids Sulfeno sulfenic acid
R 1 - SO - R 2
General structure of sulfoxides with the sulfinyl group marked blue
Sulfoxides sulfinyl sulfoxide z. B. dimethyl sulfoxide
R- COO - M +
R-C OO - M +
General structure of carboxylic acid salts
Carboxylic acid salts Metallcarboxylato-
Metal -...- carboxylate
Metal -...- oat
z. B. acetate
R - SO 2 - O - M +
General structure of sulfonic acid salts
Sulfonic acid salts Metal sulfonato Metal -...- sulfonate
R- SO-O - M +
General structure of sulfinic acid salts
Sulfinic acid salts Metal sulfinato Metal -...- sulfinate
R- S-O - M +
General structure of sulfenic acid salts
Sulfenic acid salts Metal sulfenato Metal -...- sulfenate
R 1 - CO-O-CO -R 2
General structure of the carboxylic acid anhydride
Carboxylic acid anhydrides - ...- acid ...- acid anhydride
with the same acids:
...- acid anhydride
z. B. acetic anhydride
R 1 - CO-O -R 2
General structure of the carboxylic acid ester
Carboxylic acid ester (R yl) oxycarbonyl
(R yl -) ...- carboxylate
(R yl -) ...- oat
z. B. ethyl acetate
R 1 - SO 2 - O - R 2
General structure of the sulfonic acid ester
Sulfonic acid ester (R yl-) oxysulfonyl- (R yl -) ... sulfonate
R- O-NO 2
General structure of the nitric acid ester with the blue-marked nitric acid ester (nitrate) group
Nitric acid ester z. B. nitroglycerin , nitrocellulose
General structure of the carboxylic acid halides with the halocarbonyl radical marked blue
Carboxylic acid halides Halocarbonyl
halide oyl halide
z. B. benzoyl chloride
R- SO 2 -X
General structure of the sulfonic acid halides with the halosulfonyl radical marked in blue
Sulfonic acid halides Halosulfonyl sulfonyl halide
R- CO-NH 2
R-C O-NH 2
General structure of the carboxamides with the blue marked carbamoyl residue.  R = H or organyl group
Carboxamides Carbamoyl
R- SO 2 -NH 2
General structure of the sulfonic acid amides with the sulfamoyl residue marked blue.  R = H or organyl group
Sulfonic acid amides Sulfamoyl -sulfonamide
General structure of the carboxylic acid hydrazides with the hydrazinocarbonyl residue marked blue.  R = H or organyl group
Carboxylic acid hydrazides Hydrazinocarbonyl -carbohydrazide
R- C≡N
R- C≡N
General structure of nitriles
Nitriles Cyan
z. B. acetonitrile
General structure of aldehydes with the aldehyde (formyl) group marked in blue
Aldehydes Formyl
z. B. formaldehyde , acetaldehyde
General structure of thioaldehydes with the thioaldehyde group marked in blue
Thioaldehydes Thioformyl-
R 1 - CO - R 2
General structure of the ketones with the carbonyl group marked in blue
Ketones Oxo- -on z. B. acetone
R 1 - CS -R 2
General structure of the thioketones with the thiocarbonyl group marked in blue
Thioketones Thioxo- -thione
R 1 R 2 - C = N-OH
General structure of the oximes with the oxime group marked in blue.  R = H or organyl group
Oximes Hydroxyimino -aloxime
- (carb) aldehyde
oxime -onoxime
R 1 R 2 - C = N - NH 2
General structure of the hydrazones with the hydrazo group marked in blue.  R = H or organyl group
Hydrazones Hydrazono -alhydrazone
- (carb) aldehydhydrazone
R - OH
General structure of the hydroxyl group (marked in blue)
Alcohols and phenols Hydroxy -oil Alcohols
e.g. B. methanol , ethanol ,
isopropanol , phenol
R - SH
General structure of the thiols with the thio (mercapto) group marked in blue
Thiols Sulfanyl-
old: mercapto-
Thioalcohols , thiophenols
e.g. B. methyl mercaptan
R - NH 2
General structure of the amines with the amino group marked in blue
Amines Amino -amin z. B. aniline , amino acids
R 1 R 2 - C = N -R 3
General structure of the imines with the imino group marked in blue.  R = H or organyl group
Imine Imino -imin
R- NH-NH 2
General structure of hydrazines with the hydrazino group marked in blue
Hydrazines Hydrazino -hydrazine
R 1 - O - R 2
General structure of ethers
Ether (R 2 yl) -oxy- (R 1 yl) - (R 2 yl) ether z. B. diethyl ether , dioxane
R 1 - S -R 2
General structure of the thioethers
Thioether (R 2 yl) -thio- (R 1 yl) - (R 2 yl) sulfide
R- (O) C-NR-C (O) -R Imide

Functional groups without priority

The following functional groups are generally only used as prefixes:

Semi-structural formula Structural formula Substance class prefix Examples
R- X
General structure of halogenated hydrocarbons with halogen marked in blue = F, Cl, Br, I
Halogenated hydrocarbons Halogen- Chlorofluorocarbons
e.g. B. Frigen , chloroform
R- NO 2
General structure of the nitro compounds with the nitro group marked in blue
Nitro compounds Nitro Nitrites
e.g. B. Trinitrotoluene (TNT)
General structure of the nitroso compounds with the blue marked nitroso group
Nitroso compounds Nitrosyl
R 1 - NN - R 2
General structure of the azo compounds with the blue-marked azo group
Azo compounds Azo Azo dyes
e.g. B. Yellow Orange S
R 1 R 2 - CNN
General structure of the diazo compounds with the diazo group marked in blue.  R = H or organyl group
Diazo compounds Diazo z. B. diazomethane
R– NN + Z -
General structure of the diazonium salts with an unspecified anion Z
Diazonium salts Diazonium
R - NC
General structure of the isocyanides
Isocyanides Isocyanate
General structure of the cyanates
Cyanates Cyanato
General structure of isocyanates
Isocyanates Isocyanato
General structure of thiocyanates
Thiocyanates Thiocyanato
General structure of isothiocyanates
Isothiocyanates Isothiocyanato
General structure of hydroperoxides
Hydroperoxides Hydroperoxy
R 1 - OO - R 2
General structure of peroxides with the peroxide group marked in blue
Peroxides (R-) dioxy-

Special case of multiple ties

The multiple bonds between two carbon atoms are also counted among the functional groups :

Semi-structural formula Surname prefix Ending Examples
R- C = C- R Double bond "-enyl" "-En" z. B. Ethene
R- C≡C -R Triple bond "-inyl" "-in" z. B. ethine

From the nomenclature point of view , multiple bonds are generally regarded as part of the parent system.

Alternative nomenclature systems

In addition to this nomenclature system, there are other, less common or outdated nomenclature systems. One of them is e.g. B. the radical functional nomenclature , according to the z. B. chloromethane can be designated as methyl chloride or ethanol as ethyl alcohol .

Individual evidence

  1. Entry on functional group . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.F02555 .
  2. ^ Rainer Beckert et al .: Organikum . 22nd edition. Wiley-VCH, Weinheim 2004, ISBN 3-527-31148-3 , p. 137.


  • Günter Baars, Roland Franik, Walter Jansen, Hans Pickel, Georg Schwedt, Herbert Sommerfeld: Handbook of experimental chemistry: Secondary level II. Volume 10: Functional groups, fats, dyes. (Editors: Walter Jansen, Rudolf G Weissenhorn, Wolfgang Glöckner), Aulis, Hallbergmoos 2008, ISBN 978-3-7614-2388-2 .
  • Dieter Hellwinkel: The systematic nomenclature of organic chemistry: Instructions for use . 4th edition. Springer, Berlin 1998, ISBN 3-540-63221-2 .

Web links

Wiktionary: functional group  - explanations of meanings, word origins, synonyms, translations