The functional group is the group of atoms that characterize a chemical function and that have well-defined characteristic properties.
In organic chemistry, the functional group is a set of submolecular structures, characterized by a specific elementary connectivity and composition that confers specific chemical reactivity to the molecule that contains them. These structures replace the hydrogen atoms lost by saturated hydrocarbon chains. Aliphatic, or open chain, groups are usually represented generically by R (alkyl radicals), while aromatic ones, or derivatives of benzene, are represented by Ar (aryl radicals).
