Functionality (chemistry)

Monofunctional compounds
Methyl acetate
Thiophenol
Ethylamine

Difunctional compounds
Malonic acid
Ethanolamine
Glycine

Trifunctional compounds
Glycerol
(R)-Cysteine

In chemistry, functionality is the presence of functional groups in a molecule. In organic chemistry (and other fields of chemistry) functionality of a molecule has a decisive influence on its reactivity. In polymer chemistry the functionality of a monomer means its number of polymerizable groups, it affects the formation and the degree of crosslinking of polymers.

A monofunctional molecule possesses one function, a difunctional two, a trifunctional three, etc.

Functionality in organic chemistry and material science

In organic chemistry, functionality is often used as a synonym for functional group. For example, a hydroxyl group can also be called a HO-function.^[1][2]

Functionalisation means the introduction of functional groups, for example

• the functionalisation of a surface^[3] (e. g. silanization for the specific modification of the adhesion of a surface)
• the functionalization of nanoparticles of a metal or metal oxide to stabilize such nanoparticles^[4] or
• the so-called C-H functionalization,^[5] which means the substitution of a C-H bond by a functional group, bonded at the same carbon atom

Functionality in polymer chemistry

According to IUPAC, the functionality of a monomer is defined as the number of bonds that a monomer's repeating unit forms in a polymer with other monomers. Thus in the case of a functionality of f = 2 a linear polymer is formed by polymerizing (a thermoplastic). Monomers with a functionality f ≥ 3 lead to a branching point, which can lead to cross-linked polymers (a thermosetting polymer). Monofunctional monomers do not exist as such molecules lead to a chain termination.^[6]

From the average functionality of the used monomers the reaching of the gel point can be calculated as a function of reaction progress.^[7] Side reactions may increase or decrease the functionality.^[8]

However, IUPAC definition and the use of the term in organic chemistry differ with respect to the functionality of a double bond.^[6][9] In polymer chemistry, a double bond possesses a functionality of two (because two points of contact for further polymer chains are present, on each of the two adjacent carbon atoms), while in organic chemistry the double bond is a functional group and thus has a functionality of one.

See also

• Functional group

References

1. ↑ Kurt Peter C. Vollhardt, Neil Eric Schore: Organische Chemie, S. 73 (, p. 74, at Google Books).
2. ↑ Riedel: Moderne Anorganische Chemie von Christoph Janiak, S. 401 (, p. 401, at Google Books).
3. ↑ Alexander Langner, Anthony Panarello, Sandrine Rivillon, Oleksiy Vassylyev, Johannes G. Khinast, Yves J. Chabal: Controlled Silicon Surface Functionalization by Alkene Hydrosilylation, J. Am. Chem.
4. ↑ Marie-Alexandra Neouze, Ulrich Schubert: Surface Modification and Functionalization of Metal and Metal Oxide Nanoparticles by Organic Ligands, Monatsh.
5. ↑ Dirk Steinborn: Grundlagen der metallorganischen Komplexkatalyse, S. 305 (, p. 239, at Google Books
6. 1 2 Eintrag zu functionality, f of a monomer.
7. ↑ Koltzenburg: Polymere: Synthese, Eigenschaften und Anwendungen, S. 187 (, p. 188, at Google Books).
8. ↑ Hans-Georg Elias: Makromoleküle: Chemische Struktur und Synthesen, S. 468 und 477 (, p. 468, at Google Books).
9. ↑ http://goldbook.iupac.org/CT07503.html