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Functional group
Group of atoms giving a molecule characteristic properties

In organic chemistry, a functional group is a substituent or moiety within a molecule that determines its characteristic chemical reactions. These groups have distinctive chemical properties and are connected by covalent bonds. Functional groups can influence reactivity, solubility, and molecular polarity, as seen with the hydroxyl group in sugars. They are essential in naming organic compounds using systematic nomenclature linking to parent alkanes. Functional groups also appear as ligands in coordination complexes and are key in designing chemical synthesis through retrosynthetic analysis.

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Table of common functional groups

The following is a list of common functional groups.3 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 classGroupFormulaStructural FormulaPrefixSuffixExample
AlkaneAlkylR(CH2)nHalkyl--aneEthane
AlkeneAlkenylR2C=CR2alkenyl--eneEthylene(Ethene)
AlkyneAlkynylRC≡CR′ R − C ≡ C − R ′ {\displaystyle {\ce {R-C#C-R'}}} alkynyl--yne H − C ≡ C − H {\displaystyle {\ce {H-C#C-H}}} Acetylene(Ethyne)
Benzene derivativePhenylRC6H5RPhphenyl--benzeneCumene(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 halogen

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 classGroupFormulaStructural formulaPrefixSuffixExample
haloalkanehaloRX R − X {\displaystyle {\ce {R-X}}} halo-alkyl halideChloroethane(Ethyl chloride)
fluoroalkanefluoroRF R − F {\displaystyle {\ce {R-F}}} fluoro-alkyl fluorideFluoromethane(Methyl fluoride)
chloroalkanechloroRCl R − Cl {\displaystyle {\ce {R-Cl}}} chloro-alkyl chlorideChloromethane(Methyl chloride)
bromoalkanebromoRBr R − Br {\displaystyle {\ce {R-Br}}} bromo-alkyl bromideBromomethane(Methyl bromide)
iodoalkaneiodoRI R − I {\displaystyle {\ce {R-I}}} iodo-alkyl iodideIodomethane(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 sp-hybridized oxygen (carbonyl groups) and the donating effects of sp2-hybridized oxygen (alcohol groups).

Chemical classGroupFormulaStructural formulaPrefixSuffixExample
AlcoholHydroxyROHhydroxy--olMethanol
KetoneKetoneRCOR′-oyl- (-COR′)oroxo- (=O)-oneButanone(Methyl ethyl ketone)
AldehydeAldehydeRCHOformyl- (-COH)oroxo- (=O)-alAcetaldehyde(Ethanal)
Acyl halideHaloformylRCOXcarbonofluoridoyl-carbonochloridoyl-carbonobromidoyl-carbonoiodidoyl--oyl fluoride -oyl chloride -oyl bromide -oyl iodideAcetyl chloride(Ethanoyl chloride)
CarbonateCarbonate esterROCOOR′(alkoxycarbonyl)oxy-alkyl carbonateTriphosgene(bis(trichloromethyl) carbonate)
CarboxylateCarboxylateRCOO−carboxylato--oateSodium acetate(Sodium ethanoate)
Carboxylic acidCarboxylRCOOHcarboxy--oic acidAcetic acid(Ethanoic acid)
EsterCarboalkoxyRCOOR′alkanoyloxy-oralkoxycarbonylalkyl alkanoateEthyl butyrate(Ethyl butanoate)
HydroperoxideHydroperoxyROOHhydroperoxy-alkyl hydroperoxidetert-Butyl hydroperoxide
PeroxidePeroxyROOR′peroxy-alkyl peroxideDi-tert-butyl peroxide
EtherEtherROR′alkoxy-alkyl etherDiethyl ether(Ethoxyethane)
HemiacetalHemiacetalR2CH(OR1)(OH)alkoxy -ol-al alkyl hemiacetal
HemiketalHemiketalRC(ORʺ)(OH)R′alkoxy -ol-one alkyl hemiketal
AcetalAcetalRCH(OR′)(OR″)dialkoxy--al dialkyl acetal
Ketal (or Acetal)Ketal (or Acetal)RC(OR″)(OR‴)R′dialkoxy--one dialkyl ketal
OrthoesterOrthoesterRC(OR′)(OR″)(OR‴)trialkoxy-
Heterocycle (if cyclic)Methylenedioxy(–OCH2O–)methylenedioxy--dioxole1,2-Methylenedioxybenzene(1,3-Benzodioxole)
Orthocarbonate esterOrthocarbonate esterC(OR)(OR′)(OR″)(OR‴)tetralkoxy-tetraalkyl orthocarbonateTetramethoxymethane
Organic acid anhydrideCarboxylic anhydrideR1(CO)O(CO)R2anhydrideButyric anhydride

Groups containing nitrogen

Compounds that contain nitrogen in this category may contain C-O bonds, such as in the case of amides.

Chemical classGroupFormulaStructural formulaPrefixSuffixExample
AmideCarboxamideRCONR'R"carboxamido-orcarbamoyl--amideAcetamide(Ethanamide)
AmidineAmidineR4C(NR1)(NR2R3)amidino--amidineacetamidine

(acetimidamide)

GuanidineGuanidineRNC(NR2)2)Guanidin--GuanidineGuanidinopropionic acid
AminesPrimary amineRNH2amino--amineMethylamine(Methanamine)
Secondary amineR'R"NHamino--amineDimethylamine
Tertiary amineR3Namino--amineTrimethylamine
4° ammonium ionR4N+ammonio--ammoniumCholine
HydrazoneR'R"CN2H2hydrazino--hydrazine
IminePrimary ketimineRC(=NH)R'imino--imine
Secondary ketimine RC ( = NR ″ ) R ′ {\displaystyle {\ce {RC(=NR'')R'}}} imino--imine
Primary aldimineRC(=NH)Himino--imineEthanimine
Secondary aldimineRC(=NR')Himino--imine
ImideImide(RCO)2NR'imido--imideSuccinimide(Pyrrolidine-2,5-dione)
AzideAzideRN3azido-alkyl azidePhenyl azide(Azidobenzene)
Azo compoundAzo(Diimide)RN2R'azo--diazeneMethyl orange(p-dimethylamino-azobenzenesulfonic acid)
CyanatesCyanateROCNcyanato-alkyl cyanateMethyl cyanate
IsocyanateRNCOisocyanato-alkyl isocyanateMethyl isocyanate
NitrateNitrateRONO2nitrooxy-, nitroxy-

alkyl nitrate

Amyl nitrate(1-nitrooxypentane)
NitrileNitrileRCN R − ≡ N {\displaystyle {\ce {R-\!#N}}} cyano-alkanenitrilealkyl cyanideBenzonitrile(Phenyl cyanide)
IsonitrileRNCisocyano-alkaneisonitrilealkyl isocyanide H 3 C − N + ≡ C − {\displaystyle {\ce {H3C}}{-}{\overset {+}{{\ce {N}}}}{\ce {#C^-}}} Methyl isocyanide
NitriteNitrosooxyRONOnitrosooxy-

alkyl nitrite

Isoamyl nitrite(3-methyl-1-nitrosooxybutane)
Nitro compoundNitroRNO2nitro- Nitromethane
Nitroso compoundNitrosoRNOnitroso- (Nitrosyl-) Nitrosobenzene
OximeOximeRCH=NOH OximeAcetone oxime(2-Propanone oxime)
Pyridine derivativePyridylRC5H4N

4-pyridyl(pyridin-4-yl)

3-pyridyl(pyridin-3-yl)

2-pyridyl(pyridin-2-yl)

-pyridineNicotine
Carbamate esterCarbamateRO(C=O)NR2(-carbamoyl)oxy--carbamateChlorpropham(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 classGroupFormulaStructural formulaPrefixSuffixExample
ThiolSulfhydrylRSHsulfanyl-(-SH)-thiolEthanethiol
Sulfide(Thioether)SulfideRSR'substituent sulfanyl-(-SR')di(substituent) sulfide(Methylsulfanyl)methane (prefix) orDimethyl sulfide (suffix)
DisulfideDisulfideRSSR'substituent disulfanyl-(-SSR')di(substituent) disulfide(Methyldisulfanyl)methane (prefix) orDimethyl disulfide (suffix)
SulfoxideSulfinylRSOR'-sulfinyl-(-SOR')di(substituent) sulfoxide(Methanesulfinyl)methane (prefix) orDimethyl sulfoxide (suffix)
SulfoneSulfonylRSO2R'-sulfonyl-(-SO2R')di(substituent) sulfone(Methanesulfonyl)methane (prefix) orDimethyl sulfone (suffix)
Sulfinic acidSulfinoRSO2Hsulfino-(-SO2H)-sulfinic acid2-Aminoethanesulfinic acid
Sulfonic acidSulfoRSO3Hsulfo-(-SO3H)-sulfonic acidBenzenesulfonic acid
Sulfonate esterSulfoRSO3R'(-sulfonyl)oxy-oralkoxysulfonyl-R' R-sulfonateMethyl trifluoromethanesulfonate orMethoxysulfonyl trifluoromethane (prefix)
ThiocyanateThiocyanateRSCNthiocyanato-(-SCN)substituent thiocyanatePhenyl thiocyanate
IsothiocyanateRNCSisothiocyanato-(-NCS)substituent isothiocyanateAllyl isothiocyanate
ThioketoneCarbonothioylRCSR'-thioyl-(-CSR')orsulfanylidene-(=S)-thioneDiphenylmethanethione(Thiobenzophenone)
ThialCarbonothioylRCSHmethanethioyl-(-CSH)orsulfanylidene-(=S)-thial
Thiocarboxylic acidCarbothioic S-acidRC=OSHmercaptocarbonyl--thioic S-acidThiobenzoic acid(benzothioic S-acid)
Carbothioic O-acidRC=SOHhydroxy(thiocarbonyl)--thioic O-acid
ThioesterThiolesterRC=OSR'S-alkyl-alkane-thioateS-Methyl thioacrylate(S-Methyl prop-2-enethioate)
ThionoesterRC=SOR'O-alkyl-alkane-thioate
Dithiocarboxylic acidCarbodithioic acidRCS2Hdithiocarboxy--dithioic acidDithiobenzoic acid(Benzenecarbodithioic acid)
Dithiocarboxylic acid esterCarbodithioRC=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.

Chemical classGroupFormulaStructural formulaPrefixSuffixExample
Phosphine(Phosphane)PhosphinoR3Pphosphanyl--phosphaneMethylpropylphosphane
Phosphonic acidPhosphono RP ( = O ) ( OH ) 2 {\displaystyle {\ce {RP(=O)(OH)2}}} phosphono-substituent phosphonic acidBenzylphosphonic acid
PhosphatePhosphate ROP ( = O ) ( OH ) 2 {\displaystyle {\ce {ROP(=O)(OH)2}}} phosphonooxy-orO-phosphono- (phospho-)substituent phosphateGlyceraldehyde 3-phosphate (suffix)
O-Phosphonocholine (prefix)(Phosphocholine)
PhosphodiesterPhosphateHOPO(OR)2[(alkoxy)hydroxyphosphoryl]oxy-orO-[(alkoxy)hydroxyphosphoryl]-di(substituent) hydrogen phosphateorphosphoric acid di(substituent) esterDNA
O‑[(2‑Guanidinoethoxy)hydroxyphosphoryl]‑l‑serine (prefix)(Lombricine)

Groups containing boron

Compounds containing boron exhibit unique chemistry due to their having partially filled octets and therefore acting as Lewis acids.

Chemical classGroupFormulaStructural formulaPrefixSuffixExample
Boronic acidBoronoRB(OH)2Borono-substituentboronic acidPhenylboronic acid
Boronic esterBoronateRB(OR)2O-[bis(alkoxy)alkylboronyl]-substituentboronic aciddi(substituent) ester
Borinic acidBorinoR2BOHHydroxyborino-di(substituent)borinic acid
Borinic esterBorinateR2BORO-[alkoxydialkylboronyl]-di(substituent)borinic acidsubstituent esterDiphenylborinic acid 2-aminoethyl ester(2-Aminoethoxydiphenyl borate)

Groups containing metals

Chemical classStructural formulaPrefixSuffixExample
AlkyllithiumRLi(tri/di)alkyl--lithium

methyllithium

Alkylmagnesium halideRMgX (X=Cl, Br, I)[note 1]-magnesium halide

methylmagnesium chloride

AlkylaluminiumAl2R6-aluminium

trimethylaluminium

Silyl etherR3SiOR-silyl ether

trimethylsilyl triflate

note 1 Fluorine is too electronegative to be bonded to magnesium; it becomes an ionic salt instead.

Names of radicals or moieties

These names are used to refer to the moieties themselves or to radical species, and also to form the names of halides and substituents in larger molecules.

When the parent hydrocarbon is unsaturated, the suffix ("-yl", "-ylidene", or "-ylidyne") replaces "-ane" (e.g. "ethane" becomes "ethyl"); otherwise, the suffix replaces only the final "-e" (e.g. "ethyne" becomes "ethynyl").4

When used to refer to moieties, multiple single bonds differ from a single multiple bond. For example, a methylene bridge (methanediyl) has two single bonds, whereas a methylidene group (methylidene) has one double bond. Suffixes can be combined, as in methylidyne (triple bond) vs. methylylidene (single bond and double bond) vs. methanetriyl (three double bonds).

There are some retained names, such as methylene for methanediyl, 1,x-phenylene for phenyl-1,x-diyl (where x is 2, 3, or 4),5 carbyne for methylidyne, and trityl for triphenylmethyl.

Chemical classGroupFormulaStructural formulaPrefixSuffixExample
Single bondR•Ylo-6-ylMethyl groupMethyl radical
Double bondR:?-ylideneMethylidene
Triple bondR⫶?-ylidyneMethylidyne
Carboxylic acyl radicalAcylR−C(=O)•?-oylAcetyl

See also

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References

  1. Compendium of Chemical Terminology (IUPAC "Gold Book") functional group Archived 2019-05-16 at the Wayback Machine /wiki/Compendium_of_Chemical_Terminology

  2. March, Jerry (1985). Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.). New York: Wiley. ISBN 9780471854722. OCLC 642506595. 9780471854722

  3. Brown, Theodore (2002). Chemistry: the central science. Upper Saddle River, NJ: Prentice Hall. p. 1001. ISBN 0130669970. 0130669970

  4. Moss, G. P.; W.H. Powell. "RC-81.1.1. Monovalent radical centers in saturated acyclic and monocyclic hydrocarbons, and the mononuclear EH4 parent hydrides of the carbon family". IUPAC Recommendations 1993. Department of Chemistry, Queen Mary University of London. Archived from the original on 9 February 2015. Retrieved 25 February 2015. https://web.archive.org/web/20150209155729/http://www.chem.qmul.ac.uk/iupac/ions/RC811.html

  5. "R-2. 5 Substituent Prefix Names Derived from Parent Hydrides". IUPAC. 1993. Archived from the original on 2019-03-22. Retrieved 2018-12-15. section P-56.2.1 https://www.acdlabs.com/iupac/nomenclature/93/r93_271.htm

  6. "Revised Nomenclature for Radicals, Ions, Radical Ions and Related Species (IUPAC Recommendations 1993: RC-81.3. Multiple radical centers)". Archived from the original on 2017-06-11. Retrieved 2014-12-02. https://web.archive.org/web/20170611171918/http://www.chem.qmul.ac.uk/iupac/ions/RC813.html