Functional group explained

In organic chemistry, a functional group is a 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.[1] 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.[2] 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
AlkylR(CH2)nHalkyl- -ane
Ethane
AlkenylR2C=CR2alkenyl- -ene
Ethylene
(Ethene)
AlkynylRC≡CR'R-C#C-R'alkynyl- -yneH-C#C-H
Acetylene
(Ethyne)
Benzene derivativePhenylRC6H5
RPh
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 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
haloRXR-Xhalo- alkyl halide
Chloroethane
(Ethyl chloride)
fluoroRFR-Ffluoro- alkyl fluoride
Fluoromethane
(Methyl fluoride)
chloroRClR-Clchloro- alkyl chloride
Chloromethane
(Methyl chloride)
bromoRBrR-Brbromo- alkyl bromide
Bromomethane
(Methyl bromide)
iodoRIR-Iiodo- 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 sp-hybridized oxygen (carbonyl groups) and the donating effects of sp2-hybridized oxygen (alcohol groups).

Chemical classGroupFormulaStructural formulaPrefixSuffixExample
HydroxylROHhydroxy- -ol
Methanol
KetoneRCOR'-oyl- (-COR')
or
oxo- (=O)
-one
Butanone
(Methyl ethyl ketone)
AldehydeRCHOformyl- (-COH)
or
oxo- (=O)
-al
Acetaldehyde
(Ethanal)
HaloformylRCOXcarbonofluoridoyl-
carbonochloridoyl-
carbonobromidoyl-
carbonoiodidoyl-
-oyl fluoride
-oyl chloride
-oyl bromide
-oyl iodide

Acetyl chloride
(Ethanoyl chloride)
CarbonateCarbonate esterROCOOR'(alkoxycarbonyl)oxy-alkyl carbonate
Triphosgene
(bis(trichloromethyl) carbonate)
CarboxylateRCOO
carboxylato- -oate
Sodium acetate
(Sodium ethanoate)
Carboxylic acidRCOOHcarboxy- -oic acid
Acetic acid
(Ethanoic acid)
CarboalkoxyRCOOR'alkanoyloxy-
or
alkoxycarbonyl
alkyl alkanoate
Ethyl butyrate
(Ethyl butanoate)
HydroperoxideHydroperoxyROOHhydroperoxy-alkyl hydroperoxide
tert-Butyl hydroperoxide
PeroxidePeroxyROOR'peroxy-alkyl peroxide
Di-tert-butyl peroxide
EtherROR'alkoxy-alkyl ether
Diethyl ether
(Ethoxyethane)
HemiacetalR2CH(OR1)(OH)alkoxy -ol-al alkyl hemiacetal
HemiketalRC(ORʺ)(OH)R'alkoxy -ol-one alkyl hemiketal
AcetalRCH(OR')(OR")dialkoxy--al dialkyl acetal
Ketal (or Acetal) Ketal (or Acetal)dialkoxy--one dialkyl ketal
Orthoestertrialkoxy-
Heterocycle
(if cyclic)
Methylenedioxymethylenedioxy--dioxole
1,2-Methylenedioxybenzene
(1,3-Benzodioxole)
Orthocarbonate estertetralkoxy-tetraalkyl orthocarbonate
Tetramethoxymethane
Carboxylic anhydrideanhydride
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 classGroupFormulaStructural formulaPrefixSuffixExample
CarboxamideRCONR'R"carboxamido-
or
carbamoyl-
-amide
Acetamide
(Ethanamide)
AmidineAmidineR4C(NR1)(NR2R3)amidino--amidineacetamidine(acetimidamide)
AminesPrimary amineRNH2amino- -amine
Methylamine
(Methanamine)
Secondary amineR'R"NHamino- -amine
Dimethylamine
Tertiary amineR3Namino- -amine
Trimethylamine
4° ammonium ionR4N+ammonio- -ammonium
Choline
HydrazoneR'R"CN2H2hydrazino--hydrazine
IminePrimary ketimineRC(=NH)R'imino- -imine
Secondary ketimineRC(=NR)R'imino- -imine
Primary aldimineRC(=NH)Himino- -imine
Ethanimine
Secondary aldimineRC(=NR')Himino- -imine
Imide(RCO)2NR'imido--imide
Succinimide
(Pyrrolidine-2,5-dione)
AzideAzideRN3azido- alkyl azide
Phenyl azide
(Azidobenzene)
Azo compoundAzo
(Diimide)
RN2R'azo- -diazene
Methyl orange
(p-dimethylamino-azobenzenesulfonic acid)
CyanatesROCNcyanato-alkyl cyanate
Methyl cyanate
RNCOisocyanato-alkyl isocyanate
Methyl isocyanate
NitrateRONO2nitrooxy-, nitroxy- alkyl nitrate
Amyl nitrate
(1-nitrooxypentane)
NitrileNitrileRCNR-\!#Ncyano-alkanenitrile
alkyl cyanide

Benzonitrile
(Phenyl cyanide)
RNCisocyano-alkaneisonitrile
alkyl isocyanide
\ce\overset\ce
Methyl isocyanide
NitriteNitrosooxyRONOnitrosooxy- alkyl nitrite
Isoamyl nitrite
(3-methyl-1-nitrosooxybutane)
Nitro compoundNitroRNO2nitro-  
Nitromethane
Nitroso compoundRNOnitroso- (Nitrosyl-)  
Nitrosobenzene
OximeRCH=NOH  Oxime
Acetone oxime
(2-Propanone oxime)
Pyridine derivativePyridylRC5H4N

4-pyridyl
(pyridin-4-yl)

3-pyridyl
(pyridin-3-yl)

2-pyridyl
(pyridin-2-yl)

-pyridine
Nicotine
Carbamate esterRO(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 classGroupFormulaStructural formulaPrefixSuffixExample
ThiolSulfhydrylRSHsulfanyl-
(-SH)
-thiol
Ethanethiol
Sulfide
(Thioether)
SulfideRSR'substituent sulfanyl-
(-SR')
di(substituentsulfide


(Methylsulfanyl)methane (prefix) or
Dimethyl sulfide (suffix)
DisulfideRSSR'substituent disulfanyl-
(-SSR')
di(substituentdisulfide


(Methyldisulfanyl)methane (prefix) or
Dimethyl disulfide (suffix)
SulfoxideSulfinylRSOR'-sulfinyl-
(-SOR')
di(substituentsulfoxide
(Methanesulfinyl)methane (prefix) or
Dimethyl sulfoxide (suffix)
SulfoneSulfonylRSO2R'-sulfonyl-
(-SO2R')
di(substituentsulfone
(Methanesulfonyl)methane (prefix) or
Dimethyl sulfone (suffix)
SulfinoRSO2Hsulfino-
(-SO2H)
-sulfinic acid
2-Aminoethanesulfinic acid
SulfoRSO3Hsulfo-
(-SO3H)
-sulfonic acid
Benzenesulfonic acid
SulfoRSO3R'(-sulfonyl)oxy-
or
alkoxysulfonyl-
R R-sulfonate
Methyl trifluoromethanesulfonate or
Methoxysulfonyl trifluoromethane (prefix)
ThiocyanateRSCNthiocyanato-
(-SCN)
substituent thiocyanate
Phenyl thiocyanate
RNCSisothiocyanato-
(-NCS)
substituent isothiocyanate
Allyl isothiocyanate
ThioketoneCarbonothioylRCSR'-thioyl-
(-CSR')
or
sulfanylidene-
(=S)
-thione
Diphenylmethanethione
(Thiobenzophenone)
ThialCarbonothioylRCSHmethanethioyl-
(-CSH)
or
sulfanylidene-
(=S)
-thial
Thiocarboxylic acidCarbothioic S-acidRC=OSHmercaptocarbonyl--thioic S-acid
Thiobenzoic acid
(benzothioic S-acid)
Carbothioic O-acidRC=SOHhydroxy(thiocarbonyl)--thioic O-acid
ThioesterThiolesterRC=OSR'S-alkyl-alkane-thioate
S-methyl thioacrylate
(S-methyl prop-2-enethioate)
ThionoesterRC=SOR'O-alkyl-alkane-thioate
Dithiocarboxylic acidCarbodithioic acidRCS2Hdithiocarboxy--dithioic acid
Dithiobenzoic 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- -phosphane
Methylpropylphosphane
Phosphonic acidPhosphonoRP(=O)(OH)2phosphono-substituent phosphonic acid
Benzylphosphonic acid
PhosphatePhosphateROP(=O)(OH)2phosphonooxy-
or
O-phosphono- (phospho-)
substituent phosphate
Glyceraldehyde 3-phosphate (suffix)

O-Phosphonocholine (prefix)
(Phosphocholine)
PhosphodiesterPhosphateHOPO(OR)2[(alkoxy)hydroxyphosphoryl]oxy-
or
O-[(alkoxy)hydroxyphosphoryl]-
di(substituent) hydrogen phosphate
or
phosphoric acid di(substituentester
DNA
O‑[(2‑Guanidinoethoxy)hydroxyphosphoryl]‑‑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.

Group Formula Structural formula Prefix Suffix Example
Borono RB(OH)2 Borono- substituent
boronic acid
Boronate RB(OR)2 O-[bis(alkoxy)alkylboronyl]- substituent
boronic acid
di(substituent) ester
Borino R2BOH Hydroxyborino- di(substituent)
borinic acid
Borinate R2BOR O-[alkoxydialkylboronyl]- di(substituent)
borinic acid
substituent ester

Groups containing metals

!Chemical class!Structural formula!Prefix!Suffix!Example
AlkyllithiumRLi(tri/di)alkyl--lithiummethyllithium
Alkylmagnesium halideRMgX (X=Cl, Br, I)-magnesium halidemethylmagnesium chloride
AlkylaluminiumAl2R6-aluminiumtrimethylaluminium
Silyl etherR3SiOR-silyl ethertrimethylsilyl triflate
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").

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),[3] carbyne for methylidyne, and trityl for triphenylmethyl.

Group Formula Structural formula Prefix Suffix Example
Single bond R• Ylo-[4] -yl
Double bond R: ? -ylidene
Triple bond R⫶ ? -ylidyne
Carboxylic acyl radical Acyl R−C(=O)• ? -oyl

See also

External links

Notes and References

  1. [Compendium of Chemical Terminology]
  2. Book: Brown, Theodore . Chemistry: the central science . Prentice Hall . Upper Saddle River, NJ . 2002 . 0130669970 . 1001.
  3. Web site: R-2. 5 Substituent Prefix Names Derived from Parent Hydrides. IUPAC. 1993. 2018-12-15. 2019-03-22. https://web.archive.org/web/20190322061930/https://www.acdlabs.com/iupac/nomenclature/93/r93_271.htm. live. section P-56.2.1
  4. Web site: Revised Nomenclature for Radicals, Ions, Radical Ions and Related Species (IUPAC Recommendations 1993: RC-81.3. Multiple radical centers). 2014-12-02. https://web.archive.org/web/20170611171918/http://www.chem.qmul.ac.uk/iupac/ions/RC813.html. 2017-06-11. dead.