functional group

In organic chemistry, functional groups are specific groups of atoms 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 nearby functional groups.

The word "moiety" is often used synonymously to "functional group", but according to the IUPAC definition, a moiety is a half of a molecule including substructures of functional groups. For example, an ester is divided into an alcohol and an acyl moiety, but has an ester functional group.

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 other and with the rest of the molecule by covalent bonds.

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.

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.

Examples

 acyl group
 acetyl group
 ketoacyl group
 isoprene group

Credits

 Wikipedia