Functional group

In organic chemistry, a functional group is any substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest of the molecule's composition. This enables systematic prediction of chemical reactions and behavior of chemical compounds and the design of chemical synthesis. The reactivity of a functional group can be modified by other functional groups nearby. Functional group interconversion can be used in retrosynthetic analysis to plan organic synthesis.
A functional group is a group of atoms in a molecule with distinctive chemical properties, regardless of the other atoms in the molecule. The atoms in a functional group are linked to each other and to the rest of the molecule by covalent bonds. For repeating units of polymers, functional groups attach to their nonpolar core of carbon atoms and thus add chemical character to carbon chains. Functional groups can also be charged, e.g. in carboxylate salts, which turns the molecule into a polyatomic ion or a complex ion. Functional groups binding to a central atom in a coordination complex are called ligands. Complexation and solvation are also caused by specific interactions of functional groups. In the common rule of thumb "like dissolves like", it is the shared or mutually well-interacting functional groups which give rise to solubility. For example, sugar dissolves in water because both share the hydroxyl functional group and hydroxyls interact strongly with each other. Plus, when functional groups are more electronegative than atoms they attach to, the functional groups will become polar, and the otherwise nonpolar molecules containing these functional groups become polar and so become soluble in some aqueous environment.
Combining the names of functional groups with the names of the parent alkanes generates what is termed a systematic nomenclature for naming organic compounds. In traditional nomenclature, 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-aminobutyric acid is on the third carbon of the carbon chain attached to the carboxylic acid group. IUPAC conventions call for numeric labeling of the position, e.g. 4-aminobutanoic acid. In traditional names various qualifiers are used to label isomers, for example, isopropanol is an isomer of n-propanol. The term moiety has some overlap with the term "functional group". However, a moiety is an entire "half" of a molecule, which can be not only a single functional group, but also a larger unit consisting of multiple functional groups. For example, an "aryl moiety" may be any group containing an aromatic ring, regardless of how many functional groups the said aryl has.

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

Hydrocarbons are a class of molecule that is defined by functional groups called hydrocarbyls that contain only carbon and hydrogen, but vary in the number and order of double bonds. Each one differs in type of reactivity.

Chemical class	Group	Formula	Structural Formula	Prefix	Suffix	Example
Alkane	Alkyl	R_nH		alkyl-	-ane	Ethane
Alkene	Alkenyl	R₂C=CR₂		alkenyl-	-ene	Ethylene '
Alkyne	Alkynyl		R-C#C-R'	alkynyl-	-yne	H-C#C-H Acetylene '
Benzene derivative	Phenyl	RC₆H₅ RPh		phenyl-	-benzene	Cumene

There are also a large number of branched or ring alkanes that have specific names, e.g., tert-butyl, bornyl, cyclohexyl, etc. There are several functional groups that contain an alkene such as vinyl group, allyl group, or acrylic group. 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

s are a class of molecule that is defined by a carbon–halogen bond. This bond can be relatively weak or quite stable. 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	R-X	halo-	alkyl halide	Chloroethane '
fluoroalkane	fluoro	RF	R-F	fluoro-	alkyl fluoride	Fluoromethane '
chloroalkane	chloro	RCl	R-Cl	chloro-	alkyl chloride	Chloromethane '
bromoalkane	bromo	RBr	R-Br	bromo-	alkyl bromide	Bromomethane '
iodoalkane	iodo	RI	R-I	iodo-	alkyl iodide	Iodomethane

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 and the donating effects of sp²-hybridized oxygen.

Chemical class	Group	Formula	Structural formula	Prefix	Suffix	Example
Alcohol	Hydroxy	ROH		hydroxy-	-ol	Methanol
Ketone	Ketone	RCOR′		-oyl- or oxo-	-one	Butanone '
Aldehyde	Aldehyde	RCHO		formyl- or oxo-	-al	Acetaldehyde '
Acyl halide	Haloformyl	RCOX		carbonofluoridoyl- carbonochloridoyl- carbonobromidoyl- carbonoiodidoyl-	-oyl halide	Acetyl chloride '
Carbonate	Carbonate ester	ROCOOR′		oxy-	alkyl carbonate	Triphosgene '
Carboxylate	Carboxylate	RCOO⁻		carboxylato-	-oate	Sodium acetate '
Carboxylic acid	Carboxyl	RCOOH		carboxy-	-oic acid	Acetic acid '
Ester	Carboalkoxy	RCOOR′		alkanoyloxy- or alkoxycarbonyl	alkyl alkanoate	Ethyl butyrate '
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	R₂CH		alkoxy -ol	-al alkyl hemiacetal
Hemiketal	Hemiketal	RCR′		alkoxy -ol	-one alkyl hemiketal
Acetal	Acetal	RCH		dialkoxy-	-al dialkyl acetal
Ketal	Ketal			dialkoxy-	-one dialkyl ketal
Orthoester	Orthoester			trialkoxy-
Heterocycle	Methylenedioxy			methylenedioxy-	-dioxole	1,2-Methylenedioxybenzene '
Orthocarbonate ester	Orthocarbonate ester			tetralkoxy-	tetraalkyl orthocarbonate'''	Tetramethoxymethane
Organic acid anhydride	Carboxylic anhydride				anhydride	Butyric anhydride

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	RCONR'R"		carboxamido- or carbamoyl-	-amide	Acetamide '
Amidine	Amidine	R₄C		amidino-	-amidine	acetamidine
Guanidine	Guanidine	RNC		Guanidin-	-Guanidine	Guanidinopropionic acid
Amines	Primary amine	RNH₂		amino-	-amine	Methylamine '
Amines	Secondary amine	R'R"NH		amino-	-amine	Dimethylamine
Amines	Tertiary amine	R₃N		amino-	-amine	Trimethylamine
Amines	4° ammonium ion	R₄N⁺		ammonio-	-ammonium	Choline
Amines	Hydrazone	R'R"CN₂H₂		hydrazino-	-hydrazine	Benzophenone
Imine	Primary ketimine	RCR'		imino-	-imine
Imine	Secondary ketimine	RCR'		imino-	-imine
Imine	Primary aldimine	RCH		imino-	-imine	Ethanimine
Imine	Secondary aldimine	RCH		imino-	-imine
Imide	Imide	₂NR'		imido-	-imide	Succinimide
Azide	Azide	RN₃		azido-	alkyl azide	Phenyl azide
Azo compound	Azo	RN₂R'		azo-	-diazene	Methyl orange
Cyanates	Cyanate	ROCN		cyanato-	alkyl cyanate	Methyl cyanate
Cyanates	Isocyanate	RNCO		isocyanato-	alkyl isocyanate	Methyl isocyanate
Nitrate	Nitrate	RONO₂		nitrooxy-, nitroxy-	alkyl nitrate	Amyl nitrate '
Nitrile	Nitrile	RCN	R-\!#N	cyano-	alkanenitrile alkyl cyanide	Benzonitrile '
Nitrile	Isonitrile	RNC		isocyano-	alkaneisonitrile alkyl isocyanide	Methyl isocyanide
Nitrite	Nitrosooxy	RONO		nitrosooxy-	alkyl nitrite	Isoamyl nitrite '
Nitro compound	Nitro	RNO₂		nitro-		Nitromethane
Nitroso compound	Nitroso	RNO		nitroso-		Nitrosobenzene
Oxime	Oxime	RCH=NOH			Oxime	Acetone oxime '
Pyridine derivative	Pyridyl	RC₅H₄N		4-pyridyl 3-pyridyl 2-pyridyl	-pyridine	Nicotine
Carbamate ester	Carbamate	RONR₂		oxy-	-carbamate	Chlorpropham