{{Short description|Presence of functional groups within a molecule}} {| class="wikitable floatright" id="cxmwAQ" style="text-align:center; font-size:90%" width="20%"
! Monofunctional compounds |- | [[File:Methyl-Acetate Structural Formula V1.svg|120x120px|Essigsäuremethylester]]<br> Methyl acetate |- | [[File:Thiophenol Structural Formula V1.svg|90x90px|Thiophenol]]<br> Thiophenol |- | [[File:Ethyl Amine Structural Formula V1.svg|105x105px|Ethylamin]]<br> Ethylamine |} {| class="wikitable floatright" id="cxmwHg" style="text-align:center; font-size:90%" width="20%"
! Difunctional compounds |- | [[File:Malonic Acid Structural Formula V1.svg|107x107px|Malonsäure]]<br> Malonic acid |- | 73x73px|2-Aminoethanol<br> Ethanolamine |- | [[File:Glycine Structural Formula V1.svg|90x90px|Glycin]]<br> Glycine |} {| class="wikitable floatright" id="cxmwOw" style="text-align:center; font-size:90%" width="20%"
! Trifunctional compounds |- | [[File:Glycerine Structural Formula V1.svg|100x100px|Glycerin]]<br> Glycerol |- | [[File:(R)-Cysteine Structural Formula V1.svg|91x91px|(''R'')-Cystein]]<br> (''R'')-Cysteine |}
In chemistry, '''functionality''' is the presence of functional groups in a molecule. A '''monofunctional''' molecule possesses one functional group, a '''bifunctional''' (or '''difunctional''') two, a '''trifunctional''' three, and so forth. In organic chemistry (and other fields of chemistry), a molecule's functionality has a decisive influence on its reactivity.
In polymer chemistry, the functionality of a monomer refers to its number of polymerizable groups, and affects the formation and the degree of crosslinking of polymers.
== 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.<ref>Kurt Peter C. Vollhardt, Neil Eric Schore: ''Organische Chemie'', S. 73 ({{Google books|3eIXefCwsEMC||page=74}}).</ref><ref>Riedel: ''Moderne Anorganische Chemie'' von Christoph Janiak, S. 401 ({{Google books|bW7cxciPCv4C||page=401}}).</ref>
''Functionalisation'' means the introduction of functional groups, for example * the functionalisation of a surface<ref>Alexander Langner, Anthony Panarello, Sandrine Rivillon, Oleksiy Vassylyev, Johannes G. Khinast, Yves J. Chabal: ''Controlled Silicon Surface Functionalization by Alkene Hydrosilylation'', J. Am. Chem.</ref> (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<ref name="Neouze">Marie-Alexandra Neouze, Ulrich Schubert: Surface Modification and Functionalization of Metal and Metal Oxide Nanoparticles by Organic Ligands, Monatsh.</ref> or * the so-called C-H functionalization,<ref>Dirk Steinborn: ''Grundlagen der metallorganischen Komplexkatalyse'', S. 305 ({{Google books|01bZ7l-ISJ8C||page=239}}</ref> which means the substitution of a C-H bond by a functional group, bonded at the same carbon atom
== 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.<ref name="Gold Book">Eintrag zu ''functionality, f of a monomer''.</ref>
From the average functionality of the used monomers the reaching of the gel point can be calculated as a function of reaction progress.<ref name="Koltzenburg">Koltzenburg: ''Polymere: Synthese, Eigenschaften und Anwendungen'', S. 187 ({{Google books|DSckBAAAQBAJ||page=188}}). This reference is being translated to English as "Polymer Chemistry" by the same authors, to appear in September 2017. See [https://www.springer.com/us/book/9783662492772]</ref> Side reactions may increase or decrease the functionality.<ref>Hans-Georg Elias: ''Makromoleküle: Chemische Struktur und Synthesen'', S. 468 und 477 ({{Google books|NYN9xJ47LmEC||page=468}}). </ref>
However, IUPAC definition and the use of the term in organic chemistry differ with respect to the functionality of a double bond.<ref name="Gold Book"/><ref>{{GoldBookRef |title=chemical functionality |file=CT07503 }}</ref> 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.
== References == <references />
{{Portal|Chemistry}} Category:Functional groups