Chemoselectivity

Chemoselectivity is a term in chemistry for the preferential occurrence of a chemical reaction compared to other plausible reactions. The word is particularly used in organic chemistry to describe that a functional group in one molecule reacts preferentially over another group. Chemoselectivity is a subset of the generic term reactivity of the functional groups concerned. Schematically, the facts can be represented as follows:

The molecule ( marked orange ) has three functional groups: A, B and C. The reagent (above the reaction arrow) has a structure (shape = a symbol for reactivity) that is compatible with functional group B and therefore chemoselective with it Group reacts. The other functional groups (A and C) do not react.

If a reagent only reacts with one of several functional groups, it is called "chemospecific"; Reagents with 100% chemoselectivity therefore react chemospecifically. On the other hand, a reagent that reacts with several functional groups in parallel is not very chemoselective. The chemoselectivity also depends on the reaction conditions (temperature, solvent , catalyst, etc.).

The chemoselectivity of a reaction is difficult to predict, but the evaluation of experimental experience and examples often allows a prediction. A well-known example is the reduction of carbonyl compounds, where the chemoselectivity of the reducing agent sodium borohydride clearly exceeds that of lithium aluminum hydride :

• Sodium borohydride reduces aldehydes to primary alcohols and ketones to secondary alcohols. Esters and nitriles are usually not reduced,
• Lithium aluminum hydride reduces aldehydes and esters to primary alcohols, ketones to secondary alcohols and nitriles to primary amines .

See also

• Regioselectivity
• Stereoselectivity

Individual evidence

1. ↑ Entry on chemoselectivity . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.C01051 Version: 2.3.3.
2. ^ Ulrich Lüning: Organic reactions , 2nd edition, Elsevier GmbH, Munich, 2007, pp. 139–141, ISBN 978-3-8274-1834-0 .