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Chemoselektivität ist in der Chemie ein Begriff für das bevorzugte Auftreten einer chemischen Reaktion im Vergleich zu einer anderen Reaktion. Das Wort wird besonders in der organischen Chemie angewended, um zu beschreiben, dass eine funktionelle Gruppe in einem Molekül bevorzugt gegenüber einer anderen Gruppe reagiert.[1] Die Chemoselektivität ist eine Teilmenge des Oberbegriffs Reaktivität der betreffenden funktionellen Gruppen. Schematisch kann man den Sachverhalt so darstellen:
Een reagens wordt chemoselectief genoemd als het slechts met een beperkt aantal functionele groepen reageert. Een reagens dat met zeer veel functionele groepen reageert is dus weinig selectief te noemen. Vaak is het moeilijk te voorspellen of een reactie chemoselectief zal verlopen of niet, omdat er diverse factoren (oplosmiddel, temperatuur, katalysator, orbitaalinteractie, ...) zijn die hier een invloed op kunnen hebben.Chemical reactions are defined usually in small contexts (only up to a small number of neighbouring atoms), such generalizations are a matter of utility. The preferential outcome of one instance of a generalized reaction over a set of other plausible reactions, is defined as chemoselectivity. [2]
In another definition, chemoselectivity refers to the selective reactivity of one functional group in the presence of others; often this process in convoluted and protecting groups are on the molecular connectivity alone. Such predictions based on connectivity are generally considered plausible, but the physical outcome of the actual reaction is ultimately dependent on a number of factors that are practically impossible to predict to any useful accuracy (solvent, atomic orbitals, etc.).
As such, chemoselectivity can be difficult to predict, but observing selective outcomes in cases where many reactions are plausible, is common. Examples include the selective organic reduction of the greater relative chemoselectivity of sodium borohydride reduction vs. lithium aluminium hydride reduction. In another example, the compound 4-methoxyacetophenone is oxidized by bleach at the ketone group at high pH (forming the carboxylic acid) and oxidized by EAS (to the aryl chloride) at low pH [3]
See also
[edit]References
[edit]- ^ (in English) Chemoselectivity (chemoselective), IUPAC Compendium of Chemical Terminology ('Gold Book'), 2nd Ed., 1997
- ^ IUPAC Gold Book definition for chemoselectivity.
- ^ Ballard, C. E. (2010). "pH-Controlled Oxidation of an Aromatic Ketone: Structural Elucidation of the Products of Two Green Chemical Reactions". Journal of Chemical Education. 87 (2): 190–193. Bibcode:2010JChEd..87..190B. doi:10.1021/ed800054s.