functional group

functional group

functional group, in organic chemistry, group of atoms within a molecule that is responsible for certain properties of the molecule and reactions in which it takes part. Organic compounds are frequently classified according to the functional group or groups they contain. For example, methanol, ethanol, and isopropanol are all classified as alcohols since each contains a functional hydroxyl group.

In organic chemistry, functional groups are specific groups of atoms 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. However, its relative reactivity can be modified by nearby functional groups.

The word moiety is often used synonymously to "functional group", but according to the IUPAC definition, a moiety is a half of a molecule including substructures of functional groups. For example, an ester is divided into an alcohol and an acyl moiety, but has an ester functional group. The use of the word "moiety" to mean a functional group in the chemistry sense is actually fairly recent.

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

The non-hydrogen atoms of functional groups are always associated with each other and with the rest of the molecule by covalent bonds. When the group of atoms is associated with the rest of the molecule primarily by ionic forces, the group is referred to more properly as a polyatomic ion or complex ion. And all of these are called radicals, by a meaning of the term radical that predates the free radical.

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.

Functional groups are attached to the carbon backbone of organic molecules. They determine the characteristics and chemical reactivity of molecules. Functional groups are far less stable than the carbon backbone and are likely to participate in chemical reactions.


Functional groups are used for synthesizing natural and artificial chemical compounds such as polymers and drugs. Functional groups are also used to covalently link molecules such as fluorescent dyes, nanoparticles, proteins, DNA, and other compounds of interest for a variety of applications such as sensing and basic chemical research. Functional groups are also employed for surface modification of industrial materials in order to achieve desired surface properties such as water repellent coatings for automobile windshields and non-biofouling, hydrophilic coatings for contact lenses. Additionally, functional groups are used to covalently link functional molecules to the surface of chemical and biochemical devices such as microarrays and microelectromechanical systems.

Table of common functional groups

The following is a list of common functional groups. 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 that vary based upon the number and order of π bonds impart different chemistry. Each listing below contains C-H bonds, but each one differs in type (and scope) of reactivity.

Chemical class Group Formula Structural Formula Prefix Suffix Example
Alkane Alkyl RH alkyl- -ane
Alkene Alkenyl R2C=CR2 alkenyl- -ene
Alkyne Alkynyl RC≡CR' alkynyl- -yne
Benzene derivative Phenyl RC6H5
phenyl- -benzene
Toluene derivative Benzyl RCH2C6H5
benzyl- 1-(substituent)toluene
Benzyl bromide
There are also a large number of branched or ring alkanes that have specific names, e.g. tert-butyl, bornyl, cyclohexyl, etc.

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 sp² hybridized oxygen and the donating effects of sp³ hybridized oxygen.
Chemical class Group Formula Structural Formula Prefix Suffix Example
Acyl halide Haloformyl RCOX haloformyl- -oyl halide
Acetyl chloride
(Ethanoyl chloride)
Alcohol Hydroxyl ROH hydroxy- -ol
Ketone Carbonyl RCOR' keto-, oxo- -one
Methyl ethyl ketone
Aldehyde Aldehyde RCHO aldo- -al
Carbonate Carbonate ester ROCOOR alkyl carbonate
Carboxylate Carboxylate RCOO

carboxy- -oate
Sodium acetate
(Sodium ethanoate)
Carboxylic acid Carboxyl RCOOH carboxy- -oic acid
Acetic acid
(Ethanoic acid)
Ether Ether ROR' alkoxy- alkyl alkyl ether
Diethyl ether
Ester Ester RCOOR' alkyl alkanoate
Ethyl butyrate
(Ethyl butanoate)
Hydroperoxide Hydroperoxy ROOH hydroperoxy- alkyl hydroperoxide
Methyl ethyl ketone peroxide
Peroxide Peroxy ROOR peroxy- alkyl peroxide
Di-tert-butyl peroxide

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- -amide
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 RC(=NR'')R' imino- -imine
Primary aldimine RC(=NH)H imino- -imine
Secondary aldimine RC(=NR')H imino- -imine
Imide Imide RC(=O)NC(=O)R' 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
Isocyanide RNC isocyano- alkyl isocyanide
Isocyanates Isocyanate RNCO isocyanato- alkyl isocyanate
Methyl isocyanate
Isothiocyanate RNCS isothiocyanato- alkyl isothiocyanate
Allyl isothiocyanate
Nitrate Nitrate RONO2 nitrooxy-, nitroxy- alkyl nitrate
Amyl nitrate
Nitrile Nitrile RCN cyano- alkanenitrile
alkyl cyanide

(Phenyl cyanide)
Nitrite Nitrosooxy RONO nitrosooxy- alkyl nitrite
Isoamyl nitrite
Nitro compound Nitro RNO2 nitro-  
Nitroso compound Nitroso RNO nitroso-  
Pyridine derivative Pyridyl RC5H4N





Groups containing phosphorus and sulfur

Compounds that contain sulfur and phosphorus exhibit unique chemistry due to their ability to form more bonds than nitrogen and oxygen, their lighter analogues on the periodic table.
Chemical class Group Formula Structural Formula Prefix Suffix Example
Phosphine Phosphino R3P phosphino- -phosphane
Phosphodiester Phosphate HOPO(OR)2 phosphoric acid di(substituent) ester di(substituent) hydrogenphosphate DNA
Phosphonic acid Phosphono RP(=O)(OH)2 phosphono- substituent phosphonic acid
Benzylphosphonic acid
Phosphate Phosphate ROP(=O)(OH)2 phospho-
Glyceraldehyde 3-phosphate
Sulfide or thioether RSR' di(substituent) sulfide
Dimethyl sulfide
Sulfone Sulfonyl RSO2R' sulfonyl- di(substituent) sulfone
Dimethyl sulfone
Sulfonic acid Sulfo RSO3H sulfo- substituent sulfonic acid
Benzenesulfonic acid
Sulfoxide Sulfinyl RSOR' sulfinyl- di(substituent) sulfoxide
Diphenyl sulfoxide
Thiol Sulfhydryl RSH mercapto-, sulfanyl- -thiol
(Ethyl mercaptan)
Thiocyanate Thiocyanate RSCN thiocyanato- alkyl thiocyanate
Disulfide Disulfide RSSR' alkyl alkyl disulfide
Diphenyl disulfide



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