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Updated on 01st July, 2023 , 10 min read
A functional group in organic chemistry is a substituent or moiety in a molecule that triggers the molecule's distinctive chemical processes. No matter how the rest of the molecule is made up, the same functional group will experience the same or a similar set of chemical events. This permits the design of chemical synthesis as well as the systematic prediction of chemical reactions and the behaviour of chemical molecules. Other functional groups close by can affect a functional group's reactivity. Retrosynthetic analysis can be used to design organic synthesis by using functional group interconversion.
It is referred to as a systematic nomenclature for naming organic compounds when the names of functional groups are combined with the names of the parent alkanes. The first carbon atom after the one that joins to the functional group is referred to as the alpha carbon in conventional nomenclature; the second is the beta carbon; the third is the gamma carbon, etc. According to IUPAC conventions, the position must be labelled numerically, for example, 4-aminobutanoic acid. Different qualifiers are used to identify isomers in conventional names; for instance, isopropanol (IUPAC name: propan-2-ol) is an isomer of n-propanol (propan-1-ol). The terms "functional group" and "moiety" are somewhat interchangeable. A moiety, on the other hand, is a complete "half" of a molecule and can be either a single functional group or a bigger unit made up of several functional groups. An "aryl moiety," for instance, could be any group that contains an aromatic ring, regardless of how many functional groups the aryl in question comprises.
The common functional groups are listed below. The symbols R and R' in the formulations often stand for a connected hydrogen atom or a hydrocarbon side chain of any length, though they can also occasionally stand for any combination of atoms.
Chemical class |
Group |
Formula |
Prefix |
Suffix |
Alkane |
Alkyl |
R(CH2)nH |
alkyl- |
-ane |
Alkene |
Alkenyl |
R2C=CR2 |
alkenyl- |
-ene |
Alkyne |
Alkynyl |
RC≡CR' |
alkynyl- |
-yne |
Benzene Derivative |
Phenyl |
RC6H5 RPh |
phenyl- |
-yne |
Chemical class |
Group |
Formula |
Prefix |
Suffix |
haloalkane |
halo |
RX |
halo- |
alkyl halide |
fluoroalkane |
fluoro |
RF |
fluoro- |
alkyl fluoride |
chloroalkane |
chloro |
RCl |
chloro- |
alkyl chloride |
bromoalkane |
bromo |
RBr |
bromo- |
alkyl bromide |
iodoalkane |
iodo |
RI |
iodo- |
alkyl iodide |
The hybridization of the carbon-oxygen bond determines all of the features of functional groups that contain this link.
This can be explained by the fact that the sp3 hybridised oxygen found in alcohols has an electron-donating impact, in contrast to the sp2 hybridised oxygen found in carbonyl groups with a carbon-oxygen double bond, which has an electron-withdrawing effect.
Below is a table with examples that lists the suffixes that are used in the naming of compounds that include functional groups that contain C-O bonds.
Chemical class |
Group |
Formula |
Prefix |
Suffix |
Alcohol |
Hydroxyl |
ROH |
hydroxy- |
-ol |
Carbonyl function |
Carbonyl |
CO |
- | - |
Ketone |
Ketone |
RCOR' |
-oyl- (-COR') or oxo- (=O) |
-one |
Aldehyde |
Aldehyde |
RCHO |
formyl- (-COH) or oxo- (=O) |
-al |
Acyl halide |
Haloformyl |
RCOX |
carbonofluoridoyl- carbonochloridoyl- carbonobromidoyl- carbonoiodidoyl- |
-oyl fluoride -oyl chloride -oyl bromide -oyl iodide |
Carbonate |
Carbonate ester |
ROCOOR' |
(alkoxycarbonyl)oxy- |
alkyl carbonate |
Carboxylate |
Carboxylate |
RCOO− |
carboxy- |
-oate |
Carboxylic acid |
Carboxyl |
RCOOH |
carboxy- |
-oic acid |
Ester |
Carboalkoxy |
RCOOR' |
alkanoyloxy- or alkoxycarbonyl |
alkyl alkanoate |
Hydroperoxide |
Hydroperoxy |
ROOH |
Hydroperoxy- |
alkyl hydroperoxide |
Peroxide |
Peroxy |
ROOR' |
Peroxy- |
alkyl peroxide |
Ether |
Ether |
ROR' |
alkoxy- |
alkyl ether |
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) |
RC(OR")(ORâ´)R' |
dialkoxy- |
-one dialkyl ketal |
Orthoester |
Orthoester |
RC(OR')(OR")(ORâ´) |
trialkoxy- |
- |
Heterocycle (if cyclic) |
Methylenedioxy |
(–OCH2O–) |
methylenedioxy- |
-dioxole |
Orthocarbonate ester |
Orthocarbonate ester |
C(OR)(OR')(OR")(ORâ´) |
tetralkoxy- |
tetraalkyl orthocarbonate |
Organic acid anhydride |
Carboxylic anhydride |
R1(CO)O(CO)R2 |
- |
anhydride |
Due to their capacity to make more bonds than oxygen, their lighter equivalent on the periodic table, sulfur-containing compounds display distinctive chemistry. For sulphides, disulfides, sulfoxides, and sulfones, substitutive nomenclature (noted as a prefix in the table) is preferable over functional class nomenclature (noted as a suffix in the table).
Chemical class |
Group |
Formula |
Prefix |
Suffix |
Thiol |
Sulfhydryl |
RSH |
sulfanyl- (-SH) |
-thiol |
Sulfide (Thioether) |
Sulfide |
RSR' |
substituent sulfanyl- (-SR') |
di(substituent) sulfide |
Disulfide |
Disulfide |
RSSR' |
substituent disulfanyl- (-SSR') |
di(substituent) disulfide |
Sulfoxide |
Sulfinyl |
RSOR' |
-sulfinyl- (-SOR') |
di(substituent) sulfoxide |
Sulfone |
Sulfonyl |
RSO2R' |
-sulfonyl- (-SO2R') |
di(substituent) sulfone |
Sulfinic acid |
Sulfino |
RSO2H |
sulfino- (-SO2H) |
-sulfinic acid |
Sulfonic acid |
Sulfo |
RSO3H |
sulfo- (-SO3H) |
-sulfonic acid |
Sulfonate ester |
Sulfo |
RSO3R' |
(-sulfonyl)oxy- or alkoxysulfonyl- |
R' R-sulfonate |
Thioketone |
Carbonothioyl |
RCSR' |
-thioyl- (-CSR') or sulfanylidene- (=S) |
-thione |
Thial |
Carbonothioyl |
RCSH |
methanethioyl- (-CSH) or sulfanylidene- (=S) |
-thial |
This group of nitrogen-containing compounds includes those that can have C-O bonds, like amides.
Chemical class |
Group |
Formula |
Prefix |
Suffix |
Amide |
Carboxamide |
RCONR'R" |
Carboxamido- or carbamoyl: |
-amide |
Amidine |
Amidine |
RC(NR)NR2 |
amidino- |
-amidine |
Amines |
Primary Amine |
RNH2 |
amino- |
-amine |
Secondary Amine |
R'R"NH |
amino- |
-amine |
|
Tertiary Amine |
R3N |
amino- |
-amine |
|
4° ammonium ion |
R4N+ |
ammonio- |
-ammonium |
|
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 |
(RCO)2NR' |
Imido- |
-Imide |
Azide |
Azide |
RN3 |
Azido- |
-Alkyl Azide |
Azo compound |
Azo (Dimide) |
RN2R' |
azo- |
-diazene |
Following are some of the most commonly encountered functional groups. Keep in mind that "R" stands in for a general-purpose carbon substituent.
The hydrocarbon functional groups have a tendency to be exceedingly weak acids and are highly non-polar. In contrast to molecules containing more polar functional groups, the only intermolecular interactions that occur in hydrocarbons are London dispersion forces, hence their boiling temperatures are often rather low.
Alkanes are hydrocarbons with a single bond alone. Alkyl groups, which relate to alkanes without a C-H link like methyl, ethyl, or propyl, are what are known as alkane substituents.
Alkenes are hydrocarbons that have one or more double bonds between carbon atoms.
Alkynes have a triple bond made of carbon and carbon.
Benzoene rings- Six-membered rings with three double bonds make up benzoene rings. Because of their exceptional stability and a characteristic known as aromaticity (which has nothing to do with scent), benzene rings are frequently found in nature. possibly be depicted as a hexagon with a circle as well.
Because of the higher difference in electronegativities between the bonding atoms, these functional groups are noticeably more polar.
These functional groups have stronger intermolecular pressures because of the interactions between the dipoles. The ability of alcohols and amines to form hydrogen bonds also raises the boiling temperatures of these compounds.
Alcohols with the prefix R-OH have carbon linked to the hydroxyl group.
Ethers R-O-R are composed of two carbon bonds surrounding oxygen atoms.
Alkyl halides- Functional groups for alkyl halides include R-F, R-Cl, R-Br, and R-I, where R is an alkyl group.
Amines- The functional group -NH2, -NHR, or NR2 is present in amino acids, and R is typically a hydrocarbon.
Thiols- Alcohols' sulfur-containing cousins are thiols (mercaptans) R-SH.
The carbonyl group is another name for the C=O group. The carbon contains a partial positive charge and the C=O bond is strongly polarised towards oxygen.
Aldehydes, ketones, esters, and carboxylic acids all contain carbonyls.
Aldehydes RCHO have carbon and C-H bonded by the compound C=O.
Ketone- C=O is linked to two carbons in the ketone RC(O)R.
Carboxylic Acid, a carbonyl is attached to the -OH in RCOOH. They differ from alcohols in terms of functional groups.
Esters- In contrast to carboxylic acids, esters RCOOR have an O-C bond in place of the O-H bond.
Actually, there are quite a few significant functional groups that contain carbonyls. All of these functional groups are thought to be derivations of carboxylic acids since they can be produced by substituting other groups for OH.
Amides have an amino group and a carbonyl carbon linked.
Acid Halides- F, Cl, Br, or I are used in place of -OH in acid halides.
Anhydrides- An oxygen is surrounded by two carbonyls in anhydrides. different than esters.
Nitriles- At first glance, nitriles don't appear to be derivatives of carboxylic acids, but they can be created by dehydrating amides.
There is no overarching theme here; only a few more notable functional groups that are worth knowing.
Epoxides are technically ethers, but since they take part in several reactions that ethers typically avoid, they merit their own category.
Thioethers- The sulfur equivalents of ethers are thioethers (sulfides). The example that comes up most frequently is dimethyl sulfide.
Nitro- Strong electron withdrawal occurs in nitro groups. The most straightforward nitroalkane is the solvent nitromethane.
Imines- Aldehydes and ketones' nitrogen-containing counterparts are imines.
Azides pop up from time to time. The “A” in the anti-HIV drug AZT stands for azido.
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