In organic chemistry functional groups are submolecular structural motifs, characterized by specific elemental composition and connectivity, that confer reactivity upon the molecule that contains them.
Common functional groups include:
| Group | Chemical class | Formula | Prefix | Suffix |
|---|---|---|---|---|
| Amine | Amine | R-NH2 | amino- | -amine |
| Carboxyl | Carboxylic acid | R-C(=O)OH | hydrocarboxy- | -oic acid |
| Hydroxyl | Alcohol | R-OH | hydroxy- | -ol |
| Carbonyl | Aldehyde | R-C(=O)H | -al | |
| Ketone | R-C(=O)-R' | keto- | -one | |
| Ester | Ester | R-C(=O)O-R' | named according to the parent alcohol and acid, respectively: alkyl alkanoate | |
| Ether | Ether | R-O-R' | named according to the parent alcohols, respectively: alkylalkylether | |
| Amide | Amide | R-C(=O)N(-H)-R' | name according to the parent amine and acid, respectively: alkyl alkanamide | |
| Azo | R-N=N-R' | |||
| Alkene | R-CH=CH-R' | convert the part substituting for alk in the name of the alkane into the alk of the word alkene: ethane/ethene, propane/propene, butane/butene, etc. | -ene | |
| Alkyne | R-CC-R' | convert the part substituting for alk in the name of the alkane into the alk of the word alkyne: ethane/ethyne, propane/propyne, butane/butyne, etc. | -yne | |
| Phosphodiester | R-OP(=O)2O-R' | |||
| Phenyl | R-C6H5 | |||
| Pyridyl | R-C5H4N | |||
| Nitrile | R-CN | alkyl nitrile | ||
| Isonitrile | R-NC | alkyl isonitrile | ||
| Isocyanate | R-NCO | alkyl isocyanate | ||
| Isothiocyanate | R-NCS | alkyl isothiocyanate | ||
| Methyl | R-CH3 | methyl- (similarly for higher alkyl substituents: ethyl, propyl, butyl, etc.) | ||
| Thioether | R-S-R' |
Combining the names of functional groups with the names of the parent alkanes generates a powerful systematic nomenclature for naming organic compounds.
The non-hydrogen atoms of functional groups are always associated with each by covalent bonds, as well as with the rest of the molecule. When the group of atoms is associated with the rest of the molecule primarily by ionic forces, the group is referred to more properly as a polyatomic ion or complex ion. And all of these are called radicals, by a meaning of the term radical that predates the free radical.