Intramolecular catalysis definition

Cage, solvent, 134 Cancellation assumption. 447 Catalysis, 263 acid, 453 buffer, 269 definitions of, 263 electrophilic, 265 general acid, 265, 268 general base, 265, 268, 271 intermolecular, 266 intramolecular, 266 nucleophilic, 266, 268, 271... 

Many examples of proximity effects are known. In general, whenever an intramolecular acid or base is invoked in acid-base catalysis, proximity effects can be a factor. Further, when any catalyst holds a substrate near a catalytic group at its active site, or holds two separate substrates next to each other, proximity effects can be relevant. Proximity effects are definitely prevalent in organometallic catalysis, as we will see in Chapter 12. Hence, proximity effects are key to many forms of catalysis. 

Reports on the rate enhancements in intramolecular nucleophilic reactions compared to analogous intermolecular nucleophilic reactions are plenty. But such reports on induced intramolecular or intramolecular induced nucleophilic catalysis are rare. One might argue that the induced intramolecular/intramolecular induced nucleophilic reactions also represent the corresponding nucleophilic catalysis. But this statement is not totally correct in view of the definition of a catalyst. For example, hydroxide-ion-catalyzed second-order rate constant (koe) for the cleavage of one of the two amide bonds in N,N-dimethylphthalamide (13) at 25.3°C is 7.6 sec. The value of koe for the cleavage of amide bond in... 

By definition, hydroxide ion is called a specific base and, hence, SB catalysis involves hydroxide ion as a catalyst. SB-catalyzed reactions must be only inter-molecular, because in the intramolecular catalytic reaction, the catalyst (hydroxide ion) is required to be covalently or electrovalently attached with the substrate, and under such circumstances, substrate-bound O or OH group becomes the GB catalyst. There are two possible modes of SB catalysis (1) hydroxide ion acts as a base in an acid-base reaction of overall catalytic process as shown in Scheme 2.28, and (2) hydroxide ion acts as a nucleophile in the overall catalytic process as shown in Scheme 2.29. It is evident from Scheme 2.28 that Y must be a stronger base than HO" so that hydroxide ion could not be consumed during the... 

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