Neighbor group participation

Neighbor group participation , also anchimeric support (from the Greek ἀγχί , neighboring; μέρος , part), is an effect that can be observed in intramolecular reactions in organic chemistry . A neighboring functional group has an accelerating influence on substitution reactions .

In the case of nucleophilic substitution reactions, in particular in the case of solvolysis , it can be observed that certain groups in the β position significantly increase the reaction rate - compared with the unsubstituted compound. In the β-chlorodialkyl sulfide shown as an example, the RS group is the substituent that accelerates the substitution:

The RS group accelerates such reactions the most. In the following series, the participation of the β groups in the neighboring group decreases: RS> R (O) CO> I> R ₂ N> Br> C ₆ H ₅ > RO> Cl.

α-Carboxy groups and carboxylate anions also exert a neighboring group effect, e.g. B. in the hydrolysis of α-bromocarboxylic acids. As a result of the neighboring group participation, the hydrolysis of enantiomerically pure α-bromocarboxylic acids proceeds with retention of configuration :

Other stereoselective neighboring group participations are particularly well investigated in carbohydrate chemistry.

Individual evidence

1. ↑ Jonathan Clayden, Nick Greeves, Stuart Warren: Organische Chemie , Springer Spectrum, 2013, 2nd edition, p. 1022. ISBN 978-3-642-34715-3 .
2. ^ Siegfried Hauptmann : Organic Chemistry , 2nd revised edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, pp. 185–186, ISBN 3-342-00280-8 .
3. ↑ Joachim Buddrus, Bernd Schmidt: Basics of Organic Chemistry , 5th edition, de Gruyter Verlag, Berlin, 2015, pp. 768–769, ISBN 978-3-11-030559-3 .