What is "functional group"

n. 1 (context organic chemistry English) A specific grouping of elements that is characteristic of a class of compounds, and determines some properties and reactions of that class. 2 (context ecology English) A collection of organisms of specific morphological, physiological, behavioral, biochemical properties.

In organic chemistry, functional groups are specific groups ( moieties) of atoms or bonds within molecules that are responsible for the characteristic chemical reactions 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. 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 bonds. When the group of covalently bound atoms bears a net charge, the group is referred to more properly as a polyatomic ion or a complex ion. Any subgroup of atoms of a compound also may be called a radical, and if a covalent bond is broken homolytically, the resulting fragment radicals are referred as free radicals.

Combining the names of functional groups with the names of the parent alkanes generates what is termed a systematic nomenclature for naming organic compounds. 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-aminobutanoic acid is on the third carbon of the carbon chain attached to the carboxylic acid group.

The term functional group may have several meanings:

• Functional group, in organic chemistry, a group of atoms responsible for the characteristic chemical reactions of a molecule
• Functional group (ecology), a collection of organisms
• The Party of the Functional Groups, also known as Golkar, a political party in Indonesia

In ecology, functional groups are collections of organisms based on morphological, physiological, behavioral, biochemical, environmental responses or on trophic criteria.

In ocean biogeochemical modelling, the following four criteria have been proposed:

• That the collection of organisms, called a plankton function type (PFT), should have an explicit biogeochemical role
• that the PFT should be defined by a distinct set of physiological, environmental, or nutrient requirements controlling its biomass and productivity,
• that the behavior of the PFT should have distinct effects on the performance of other PFTs, for instance, through selective depletion of nutrients or grazing, and
• that the PFT should be of quantitative importance in at least some region of the ocean.