Functional group

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

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,^[3] a moiety is a part of a molecule that may include functional groups as substructures. For example, an ester is divided into an alcohol moiety and an acyl moiety, but has an ester functional group. Also, it may be divided into carboxylate and alkyl moieties. Each moiety may carry any number of functional groups, for example methyl parahydroxybenzoate carries a phenol functional group in the acyl moiety.

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

The atoms of functional groups are linked to each other and to 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.

Synthetic chemistry

Organic reactions are facilitated and controlled by the functional groups of the reactants. In general, alkyls are 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 (the 8-carbon ideal gasoline) from the unfunctionalized alkane isobutane (a 4-carbon gas), 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 then catalytically hydrogenated to iso-octane using pressured hydrogen gas.

Crystallography

The International Union of Crystallography in its Crystallographic Information File dictionary defines "moiety" to represent discrete non-bonded components. Thus Na₂SO₄ would contain 3 moieties (2 Na⁺ and one SO₄^2-). The dictionary defines "chemical formula moiety": "Formula with each discrete bonded residue or ion shown as a separate moiety".

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. In addition, 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, wherein 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.

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.

Hydrocarbons

Functional groups, called hydrocarbyls, that contain only carbon and hydrogen, but vary in the number and order of π bonds. Each one differs in type (and scope) of reactivity.

Chemical class	Group	Formula	Structural Formula	Prefix	Suffix	Example
Alkane	Alkyl	RH		alkyl-	-ane	Ethane
Alkene	Alkenyl	R2C=CR2		alkenyl-	-ene	Ethylene (Ethene)
Alkyne	Alkynyl	RC≡CR'		alkynyl-	-yne	Acetylene (Ethyne)
Benzene derivative	Phenyl	RC6H5 RPh		phenyl-	-benzene	Cumene (2-phenylpropane)
Toluene derivative	Benzyl	RCH2C6H5 RBn		benzyl-	1-(substituent)toluene	Benzyl bromide (1-Bromotoluene)

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	Chloroethane (Ethyl chloride)
fluoroalkane	fluoro	RF		fluoro-	alkyl fluoride	Fluoromethane (Methyl fluoride)
chloroalkane	chloro	RCl		chloro-	alkyl chloride	Chloromethane (Methyl chloride)
bromoalkane	bromo	RBr		bromo-	alkyl bromide	Bromomethane (Methyl bromide)
iodoalkane	iodo	RI		iodo-	alkyl iodide	Iodomethane (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	Methanol
Ketone	Carbonyl	RCOR'		keto-, oxo-	-one	Methyl ethyl ketone (Butanone)
Aldehyde	Aldehyde	RCHO		aldo-	-al	Acetaldehyde (Ethanal)
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-	-ether	Diethyl ether (Ethoxyethane)
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	Acetamide (Ethanamide)
Amines	Primary amine	RNH2		amino-	-amine	Methylamine (Methanamine)
	Secondary amine	R2NH		amino-	-amine	Dimethylamine
	Tertiary amine	R3N		amino-	-amine	Trimethylamine
	4° ammonium ion	R4N+		ammonio-	-ammonium	Choline
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 (Azidobenzene)
Azo compound	Azo (Diimide)	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 (1-nitrooxypentane)
Nitrile	Nitrile	RCN		cyano-	alkanenitrile alkyl cyanide	Benzonitrile (Phenyl cyanide)
Nitrite	Nitrosooxy	RONO		nitrosooxy-	alkyl nitrite	Isoamyl nitrite (3-methyl-1-nitrosooxybutane)
Nitro compound	Nitro	RNO2		nitro-		Nitromethane
Nitroso compound	Nitroso	RNO		nitroso-		Nitrosobenzene
Pyridine derivative	Pyridyl	RC5H4N		4-pyridyl (pyridin-4-yl) 3-pyridyl (pyridin-3-yl) 2-pyridyl (pyridin-2-yl)	-pyridine	Nicotine

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	Methylpropylphosphane
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 (Methylsulfonylmethane)
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	Ethanethiol (Ethyl mercaptan)
Thiocyanate	Thiocyanate	RSCN		thiocyanato-	alkyl thiocyanate
Disulfide	Disulfide	RSSR'			alkyl alkyl disulfide	Diphenyl disulfide 1,2-diphenyldisulfane

See also

• For a list of all functional groups: Category:Functional groups

References

External links

• IUPAC Blue Book (organic nomenclature)
• IUPAC ligand abbreviations (pdf)
• _chemical_formula_moiety in CIF dictionary
• Functional group synthesis from organic-reaction.com