# Functional group By [Senia](https://paragraph.com/@senia) · 2023-05-30 --- In [organic chemistry](https://en.wikipedia.org/wiki/Organic_chemistry), a **functional group** is a [substituent](https://en.wikipedia.org/wiki/Substituent) or [moiety](https://en.wikipedia.org/wiki/Moiety_\(chemistry\)) in a [molecule](https://en.wikipedia.org/wiki/Molecule) that causes the molecule's characteristic [chemical reactions](https://en.wikipedia.org/wiki/Chemical_reaction). The same functional group will undergo the same or similar chemical reactions regardless of the rest of the molecule's composition.[\[1\]](https://en.wikipedia.org/wiki/Functional_group#cite_note-1)[\[2\]](https://en.wikipedia.org/wiki/Functional_group#cite_note-2) This enables systematic prediction of chemical reactions and behavior of [chemical compounds](https://en.wikipedia.org/wiki/Chemical_compound) and the design of [chemical synthesis](https://en.wikipedia.org/wiki/Chemical_synthesis). The [reactivity](https://en.wikipedia.org/wiki/Reactivity_\(chemistry\)) of a functional group can be modified by other functional groups nearby. Functional group interconversion can be used in [retrosynthetic analysis](https://en.wikipedia.org/wiki/Retrosynthetic_analysis) to plan [organic synthesis](https://en.wikipedia.org/wiki/Organic_synthesis). [https://opensea.io/assets/0xbe352d4E2519f3FacEa7dBEBd71f3Fb717C54628/2](https://opensea.io/assets/0xbe352d4E2519f3FacEa7dBEBd71f3Fb717C54628/2) A functional group is a group of atoms in a molecule with distinctive [chemical properties](https://en.wikipedia.org/wiki/Chemical_property), regardless of the other [atoms](https://en.wikipedia.org/wiki/Atom) in the molecule. The atoms in a functional group are linked to each other and to the rest of the molecule by [covalent bonds](https://en.wikipedia.org/wiki/Covalent_bond). For repeating units of [polymers](https://en.wikipedia.org/wiki/Polymer), functional groups attach to their [nonpolar](https://en.wikipedia.org/wiki/Chemical_polarity) core of [carbon](https://en.wikipedia.org/wiki/Carbon) atoms and thus add chemical character to carbon chains. Functional groups can also be [charged](https://en.wikipedia.org/wiki/Ionization), e.g. in [carboxylate](https://en.wikipedia.org/wiki/Carboxylate) salts (–COO−), which turns the molecule into a [polyatomic ion](https://en.wikipedia.org/wiki/Polyatomic_ion) or a [complex ion](https://en.wikipedia.org/wiki/Coordination_complex). Functional groups binding to a central atom in a coordination complex are called [_ligands_](https://en.wikipedia.org/wiki/Ligand). Complexation and [solvation](https://en.wikipedia.org/wiki/Solvation) are 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](https://en.wikipedia.org/wiki/Solubility). For example, [sugar](https://en.wikipedia.org/wiki/Sugar) dissolves in water because both share the [hydroxyl](https://en.wikipedia.org/wiki/Hydroxy_group) functional group (–OH) and hydroxyls interact strongly with each other. Plus, when functional groups are more [electronegative](https://en.wikipedia.org/wiki/Electronegativity) than atoms they attach to, the functional groups will become polar, and the otherwise nonpolar molecules containing these functional groups become polar and so become soluble in some [aqueous](https://en.wikipedia.org/wiki/Aqueous_solution) environment. Combining the names of functional groups with the names of the parent [alkanes](https://en.wikipedia.org/wiki/Alkane) generates what is termed a [systematic nomenclature](https://en.wikipedia.org/wiki/Systematic_name) for naming [organic compounds](https://en.wikipedia.org/wiki/Organic_compound). In traditional nomenclature, the first carbon atom after the carbon that attaches to the functional group is called the [alpha carbon](https://en.wikipedia.org/wiki/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](https://en.wikipedia.org/wiki/Gamma-aminobutyric_acid) is on the third carbon of the carbon chain attached to the carboxylic acid group. [IUPAC conventions](https://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry) call for numeric labeling of the position, e.g. 4-aminobutanoic acid. In traditional names various qualifiers are used to label [isomers](https://en.wikipedia.org/wiki/Isomer), for example, isopropanol (IUPAC name: propan-2-ol) is an isomer of n-propanol (propan-1-ol). The term [moiety](https://en.wikipedia.org/wiki/Moiety_\(chemistry\)) has some overlap with the term "functional group". However, a moiety is an entire "half" of a molecule, which can be not only a single functional group, but also a larger unit consisting of multiple functional groups. For example, an "aryl moiety" may be any group containing an [aromatic ring](https://en.wikipedia.org/wiki/Aromaticity), regardless of how many functional groups the said aryl has. Table of common functional groups --------------------------------- The following is a list of common functional groups.[\[3\]](https://en.wikipedia.org/wiki/Functional_group#cite_note-3) In the formulas, the symbols R and R' usually denote an attached hydrogen, or a [hydrocarbon](https://en.wikipedia.org/wiki/Hydrocarbon) [side chain](https://en.wikipedia.org/wiki/Side_chain) of any length, but may sometimes refer to any group of atoms. ### Hydrocarbons Hydrocarbons are a class of molecule that is defined by functional groups called [hydrocarbyls](https://en.wiktionary.org/wiki/hydrocarbyl) 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. --- *Originally published on [Senia](https://paragraph.com/@senia/functional-group)*