Anchimeric assistance neighbouring group participation

Neighbouring group participation is occasionaiiy oaiied anchimeric assistance (Greek anchi = neighbouring mer= part). 

This influence of the nitrogen ion is known as neighbouring group participation or anchimeric assistance. 

Figure 8.46 Schematic illustration to show the principle of intramolecular catalysis. Rate of reaction between the two substrates is enabled by binding and close proximity in the active site region (a). Neighbouring group participation involving neighbouring functional group assistance provides additional rate enhancement (anchimeric assistance) (b) for bond construction (c).

Neighbouring group participation is occasionally called anchimeric assistance... 

Summary This is an example of anchimeric assistance (also called neighbouring group participation) in nucleophilic substitution reactions... 

Keywoids Anchimeric assistance. Carbohydrates, Deamination, Fragmentation, Group migration, Neighbouring group participation. Nucleophilic substitution. Rearrangement, Ring contraction, Sulfonate displacement... 

A theoretical study of neighbouring carbonyl group participation in the elimination kinetics of chloroketones in the gas-phase has been performed. Results for 4-chlorobutan-2-one suggest a non-synchronous process by way of a four-membered cyclic TS. However, in the case of 5-chloropentan-2-one and4-chloro-l-phenylbutan-1-one, the carbonyl group assists C-Cl bond polarization anchimerically through a polar five-membered cyclic TS (Scheme 1). 

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