In organic chemistry
, functional groups
are specific groups ( moieties
) of atom
s or bonds within molecule
s that are responsible for the characteristic chemical reaction
s of those molecules. The same functional group will undergo the same or similar chemical reaction(s) regardless of the size of the molecule it is a part of. Compendium of Chemical Terminology
(IUPAC "Gold Book") http://goldbook.iupac.org/F02555.html However, its relative reactivity can be modified by other functional groups nearby. The atoms of functional groups are linked to each other and to the rest of the molecule by covalent bond
s. Functional groups can also be charged, e.g. in carboxylate salts (–COO−), 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
is 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 (–OH) and hydroxyls interact strongly with each other.
Combining the names of functional groups with the names of the parent alkane
s generates what is termed a systematic nomenclature
for naming organic compound
s. 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).
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.
Functional groups, called , 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.
There are also a large number of branched or ring alkanes that have specific names, e.g., tert-butyl
, etc. Hydrocarbons may form charged structures: positively charged carbocation
s or negative carbanion
s. Carbocations are often named -um
. Examples are tropylium
cations and the cyclopentadienyl
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 reaction
s. The substitution on the carbon, the acidity of an adjacent proton, the solvent conditions, etc. all can influence the outcome of the reactivity.
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).
Groups containing nitrogen
Compounds that contain nitrogen in this category may contain C-O bonds, such as in the case of amide
Groups containing sulfur
Compounds that contain sulfur exhibit unique chemistry due to their ability to form more bonds than oxygen, their 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.
Groups containing phosphorus
Compounds that contain phosphorus exhibit unique chemistry due to their ability to form more bonds than nitrogen, their lighter analogues on the periodic table.
Groups containing boron
Compounds containing boron exhibit unique chemistry due to their having partially filled octets and therefore acting as Lewis acid
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
Note that 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 methylene 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 single 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), section P-56.2.1 carbyne
for methylidyne, and trityl