Functional group

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Benzyl acetate has an ester functional group (in red), an acetyl moiety (circled with green) and a benzyl alcohol moiety (circled with orange).

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.[1][2] 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,[citation needed] 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.

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.


[edit] Synthetic chemistry

Organic reactions are facilitated and controlled by the functional groups of the reactants. Alkyls are generally unreactive and difficult to get to react selectively at the desired positions, with few exceptions. In contrast, unsaturated carbon functional groups, and carbon-oxygen and carbon-nitrogen functional groups have a more diverse array of reactions that are also selective. It may be necessary to create a functional group in the molecule to make it react. For example, to synthesize iso-octane (8-carbon) from the unfunctionalized alkane isobutane (4-carbon), isobutane is first dehydrogenated into isobutene. This contains the alkene functional group and can now dimerize with another isobutene to give iso-octene, which is hydrogenated to octane.

[edit] Functionalization

Functionalization is the addition of functional groups onto the surface of a material by chemical synthesis methods. The functional group added can be subjected to ordinary synthesis methods to attach virtually any kind of organic compound onto the surface.

Functionalization is 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.

Catalysts can be attached to a material that has been functionalized. For example, silica is functionalized with an alkyl silicone, where the alkyl contains an amine functional group. A ligand such as an EDTA fragment is synthesized onto the amine, and a metal cation is complexed into the EDTA fragment. The EDTA is not adsorbed onto the surface, but connected by a permanent chemical bond.

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.

[edit] 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.

[edit] Hydrocarbons

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 alkyl- -ane methane
Alkene Alkenyl R2C=CR2 Alkene alkenyl- -ene ethylene
Alkyne Alkynyl RC≡CR' Alkyne alkynyl- -yne acetylene
Benzene derivative Phenyl RC6H5
Phenyl phenyl- -benzene Cumene
Toluene derivative Benzyl RCH2C6H5
Benzyl benzyl- 1-(substituent)toluene Benzyl bromide
Benzyl bromide

There are also a large number of branched or ring alkanes that have specific names, e.g. tert-butyl, bornyl, cyclohexyl, etc.

[edit] 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 Halide group halo- alkyl halide Chloroethane
(Ethyl chloride)
fluoroalkane fluoro RF Fluoro group fluoro- alkyl fluoride Fluoromethane
(Methyl fluoride)
chloroalkane chloro RCl Chloro group chloro- alkyl chloride Chloromethane
(Methyl chloride)
bromoalkane bromo RBr Bromo group bromo- alkyl bromide Bromomethane
(Methyl bromide)
iodoalkane iodo RI Iodo group iodo- alkyl iodide Iodomethane
(Methyl iodide)

[edit] 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 Acyl halide haloformyl- -oyl halide Acetyl chloride
Acetyl chloride
(Ethanoyl chloride)
Alcohol Hydroxyl ROH Hydroxyl hydroxy- -ol methanol
Ketone Carbonyl RCOR' Ketone keto-, oxo- -one Butanone
Methyl ethyl ketone
Aldehyde Aldehyde RCHO Aldehyde aldo- -al acetaldehyde
Carbonate Carbonate ester ROCOOR Carbonate alkyl carbonate
Carboxylate Carboxylate RCOO Carboxylate


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

[edit] 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 Amide carboxamido- -amide acetamide
Amines Primary amine RNH2 Primary amine amino- -amine methylamine
Secondary amine R2NH Secondary amine amino- -amine dimethylamine
Tertiary amine R3N Tertiary amine amino- -amine trimethylamine
4° ammonium ion R4N+ Quaternary ammonium cation ammonio- -ammonium choline
Imine Primary ketimine RC(=NH)R' Imine imino- -imine
Secondary ketimine RC(=NR)R' Imine imino- -imine
Primary aldimine RC(=NH)H Imine imino- -imine
Secondary aldimine RC(=NR')H Imine imino- -imine
Imide Imide RC(=O)NC(=O)R' Imide imido- -imide
Azide Azide RN3 Organoazide azido- alkyl azide Phenyl azide
Phenyl azide
Azo compound Azo
RN2R' Azo.pngl azo- -diazene Methyl orange
Methyl orange
(p-dimethylamino-azobenzenesulfonic acid)
Cyanates Cyanate ROCN Cyanate cyanato- alkyl cyanate Methyl cyanate
Isocyanide RNC Isocyanide isocyano- alkyl isocyanide
Isocyanates Isocyanate RNCO Isocyanate isocyanato- alkyl isocyanate Methyl isocyanate
Methyl isocyanate
Isothiocyanate RNCS Isothiocyanate isothiocyanato- alkyl isothiocyanate Allyl isothiocyanate
Allyl isothiocyanate
Nitrate Nitrate RONO2 Nitrate nitrooxy-, nitroxy-

alkyl nitrate

Amyl nitrate
Amyl nitrate
Nitrile Nitrile RCN Nitrile cyano-

alkyl cyanide

(Phenyl cyanide)
Nitrite Nitrosooxy RONO Nitrite nitrosooxy-

alkyl nitrite

Amyl nitrite
Isoamyl nitrite
Nitro compound Nitro RNO2 Nitro nitro-   Nitromethane
Nitroso compound Nitroso RNO Nitroso nitroso-   Nitrosobenzene
Pyridine derivative Pyridyl RC5H4N

4-pyridyl group
3-pyridyl group
2-pyridyl group




-pyridine Nicotine

[edit] 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 A tertiary phosphine phosphino- -phosphane Methylpropylphosphane
Phosphodiester Phosphate HOPO(OR)2 Phosphodiester phosphoric acid di(substituent) ester di(substituent) hydrogenphosphate DNA
Phosphonic acid Phosphono RP(=O)(OH)2 Phosphono group phosphono- substituent phosphonic acid Benzylphosphonic acid
Benzylphosphonic acid
Phosphate Phosphate ROP(=O)(OH)2 Phosphate group phospho- Glyceraldehyde 3-phosphate
Glyceraldehyde 3-phosphate
Sulfide or thioether RSR' Sulfide group di(substituent) sulfide Dimethyl sulfide
Dimethyl sulfide
Sulfone Sulfonyl RSO2R' Sulfonyl group sulfonyl- di(substituent) sulfone Dimethyl sulfone
Dimethyl sulfone
Sulfonic acid Sulfo RSO3H Sulfonyl group sulfo- substituent sulfonic acid Benzenesulfonic acid
Benzenesulfonic acid
Sulfoxide Sulfinyl RSOR' Sulfinyl group sulfinyl- di(substituent) sulfoxide Diphenyl sulfoxide
Diphenyl sulfoxide
Thiol Sulfhydryl RSH Sulfhydryl mercapto-, sulfanyl- -thiol Ethanethiol
(Ethyl mercaptan)
Thiocyanate Thiocyanate RSCN Thiocyanate thiocyanato- alkyl thiocyanate
Disulfide Disulfide RSSR' Disulfide alkyl alkyl disulfide Diphenyl disulfide
Diphenyl disulfide

[edit] Other

[edit] References

  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 

[edit] External links

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