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.Compendium of Chemical Terminology (IUPAC "Gold Book") functional group 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 (IUPAC name: propan-2-ol) is an isomer of n-propanol (propan-1-ol). 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 (and scope) of reactivity.
Chemical class Group Formula Structural Formula Prefix Suffix Example Alkane Alkyl R(CH2)nH alkyl- -ane Ethane Alkene Alkenyl R2C=CR2 alkenyl- -ene Ethylene(Ethene) Alkyne Alkynyl R-C#C-R' alkynyl- -yne H-C#C-HAcetylene(Ethyne) Benzene derivative Phenyl RC6H5RPh phenyl- ‑benzene Cumene(Isopropylbenzene) 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 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 R-X halo- alkyl halide Chloroethane(Ethyl chloride) fluoroalkane fluoro RF R-F fluoro- alkyl fluoride Fluoromethane(Methyl fluoride) chloroalkane chloro RCl R-Cl chloro- alkyl chloride Chloromethane(Methyl chloride) bromoalkane bromo RBr R-Br bromo- alkyl bromide Bromomethane(Methyl bromide) iodoalkane iodo RI R-I 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 (carbonyl groups) and the donating effects of sp³-hybridized oxygen (alcohol groups). Chemical class Group Formula Structural formula Prefix Suffix Example Alcohol Hydroxy ROH hydroxy- -ol Methanol Ketone Ketone RCOR′ -oyl- (-COR′)oroxo- (=O) -one Butanone(Methyl ethyl ketone) Aldehyde Aldehyde RCHO formyl- (-COH)oroxo- (=O) -al Acetaldehyde(Ethanal) Acyl halide Haloformyl RCOX carbonofluoridoyl-carbonochloridoyl-carbonobromidoyl-carbonoiodidoyl- -oyl halide Acetyl chloride(Ethanoyl chloride)Carbonate Carbonate ester ROCOOR′ (alkoxycarbonyl)oxy- alkyl carbonate Triphosgene(bis(trichloromethyl) carbonate) Carboxylate Carboxylate RCOO− carboxylato- -oate Sodium acetate(Sodium ethanoate) Carboxylic acid Carboxyl RCOOH carboxy- -oic acid Acetic acid(Ethanoic acid) Ester Carboalkoxy RCOOR′ alkanoyloxy-oralkoxycarbonyl alkyl alkanoate Ethyl butyrate(Ethyl butanoate) 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(Ethoxyethane) Hemiacetal Hemiacetal R2CH(OR1)(OH) alkoxy -ol -al alkyl hemiacetal Hemiketal Hemiketal RC(ORʺ)(OH)R′ alkoxy -ol -one alkyl hemiketal Acetal Acetal RCH(OR′)(OR″) dialkoxy- -al dialkyl acetal Ketal (or Acetal) Ketal (or Acetal) dialkoxy- -one dialkyl ketal Orthoester Orthoester trialkoxy- Heterocycle (if cyclic) Methylenedioxy methylenedioxy- -dioxole 1,2-Methylenedioxybenzene(1,3-Benzodioxole) 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-orcarbamoyl- -amide Acetamide(Ethanamide)AmidineAmidineR4C(NR1)(NR2R3) amidino- -amidineacetamidine (acetimidamide)GuanidineGuanidineRNC(NR2)2 Guanidin- -GuanidineGuanidinopropionic acid Amines Primary amine RNH2 amino- -amine Methylamine(Methanamine) Secondary amine R'R"NH amino- -amine Dimethylamine Tertiary amine R3N amino- -amine Trimethylamine 4° ammonium ion R4N+ ammonio- -ammonium CholineHydrazoneR'R"CN2H2hydrazino- -hydrazineBenzophenone hydrazone Imine Primary ketimine RC(=NH)R' imino- -imine Secondary ketimine RC(=NR")R' imino- -imine Primary aldimine RC(=NH)H imino- -imine Ethanimine Secondary aldimine RC(=NR')H imino- -imine Imide Imide (RCO)2NR' imido- -imide Succinimide(Pyrrolidine-2,5-dione) 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 cyanateMethyl cyanate Isocyanate RNCO isocyanato- alkyl isocyanate Methyl isocyanate Nitrate Nitrate RONO2 nitrooxy-, nitroxy- alkyl nitrate Amyl nitrate(1-nitrooxypentane)Nitrile Nitrile RCN R-\!#N cyano- alkanenitrilealkyl cyanide Benzonitrile(Phenyl cyanide) Isonitrile RNC isocyano- alkaneisonitrilealkyl isocyanide Methyl isocyanideNitriteNitrosooxy RONO nitrosooxy- alkyl nitrite Isoamyl nitrite(3-methyl-1-nitrosooxybutane) Nitro compound Nitro RNO2 nitro- Nitromethane Nitroso compound Nitroso RNO nitroso- (Nitrosyl-) Nitrosobenzene Oxime Oxime RCH=NOH Oxime Acetone oxime(2-Propanone oxime) Pyridine derivative Pyridyl RC5H4N4-pyridyl(pyridin-4-yl)
3-pyridyl(pyridin-3-yl)
2-pyridyl(pyridin-2-yl) -pyridine Nicotine Carbamate ester Carbamate RO(C=O)NR2 (-carbamoyl)oxy- -carbamate Chlorpropham(Isopropyl (3-chlorophenyl)carbamate)
Groups containing sulfur Compounds that contain sulfur exhibit unique chemistry due to sulfur's ability to form more bonds than oxygen, its lighter analogue on the periodic table. Substitutive nomenclature (marked as prefix in table) is preferred over functional class nomenclature (marked as suffix in table) for sulfides, disulfides, sulfoxides and sulfones. Chemical class Group Formula Structural formula Prefix Suffix Example Thiol Sulfhydryl RSH sulfanyl-(-SH) -thiol Ethanethiol Sulfide(Thioether) Sulfide RSR' substituent sulfanyl-(-SR') di(substituent) sulfide(Methylsulfanyl)methane (prefix) orDimethyl sulfide (suffix) Disulfide Disulfide RSSR' substituent disulfanyl-(-SSR') di(substituent) disulfide(Methyldisulfanyl)methane (prefix) orDimethyl disulfide (suffix) Sulfoxide Sulfinyl RSOR' -sulfinyl-(-SOR') di(substituent) sulfoxide (Methanesulfinyl)methane (prefix) orDimethyl sulfoxide (suffix) Sulfone Sulfonyl RSO2R' -sulfonyl-(-SO2R') di(substituent) sulfone (Methanesulfonyl)methane (prefix) orDimethyl sulfone (suffix) Sulfinic acid Sulfino RSO2H sulfino-(-SO2H) -sulfinic acid 2-Aminoethanesulfinic acid Sulfonic acid Sulfo RSO3H sulfo-(-SO3H) -sulfonic acid Benzenesulfonic acid Sulfonate ester Sulfo RSO3R' (-sulfonyl)oxy-oralkoxysulfonyl- R R-sulfonate| Methyl trifluoromethanesulfonate orMethoxysulfonyl trifluoromethane (prefix) |- | rowspan=2|Thiocyanate | Thiocyanate || RSCN | | thiocyanato-(-SCN) | substituent thiocyanate| Phenyl thiocyanate |- | Isothiocyanate || RNCS | | isothiocyanato-(-NCS) | substituent isothiocyanate| Allyl isothiocyanate |- | Thioketone | Carbonothioyl | RCSR' | | -thioyl-(-CSR')orsulfanylidene-(=S) | -thione| Diphenylmethanethione(Thiobenzophenone) |- | Thial | Carbonothioyl | RCSH | | methanethioyl-(-CSH)orsulfanylidene-(=S) | -thial| Thioformaldehyde (methanethial) |- |rowspan=2| Thiocarboxylic acid | Carbothioic S-acid | RC=OSH | | mercaptocarbonyl- | -thioic S-acid| Thiobenzoic acid(benzothioic S-acid) |- | Carbothioic O-acid | RC=SOH | | hydroxy(thiocarbonyl)- | -thioic O-acid| |- |rowspan=2| Thioester | Thiolester | RC=OSR'
| S-alkyl-alkane-thioate| S-Methyl thioacrylate(S-Methyl prop-2-enethioate) |- | Thionoester | RC=SOR'
| O-alkyl-alkane-thioate| |- | Dithiocarboxylic acid | Carbodithioic acid | RCS2H | | dithiocarboxy- | -dithioic acid| Dithiobenzoic acid(Benzenecarbodithioic acid) |- | Dithiocarboxylic acid ester | Carbodithio | RC=SSR'
| -dithioate'
Groups containing phosphorus Compounds that contain phosphorus exhibit unique chemistry due to the ability of phosphorus to form more bonds than nitrogen, its lighter analogue on the periodic table.