Brpnsted base/acid catalysis structure

Nevertheless, solid-state NMR can be usefiil for active site studies, which is nowadays predominantly employed for acid catalysis, e.g., with zeolites [32]. Chemical shifts obtained are related to the electronic state of the atom H-NMR data have been, for instance, used to determine acidity of Brpnsted sites in zeolites, NMR can discriminate in various environments in supported catalysts [33]. As long as the sites are sufficiently dilute, NMR intensity is directly related to concentration. Structural information is accessible by echo techniques which allow determining distances between spin sites. By analogy with IR methodology, adsorption sites have been investigated with probe molecules also in NMR studies. While work with N bases may require isotopic enrichment of the probe, there are opportunities to detect subtle structural features by cross-polarization and doubleresonance (e.g., " N/ A1) techniques [34]. 

During the past decade, Brpnsted acid catalysis has been employed successfully to promote versatile cascade processes, efficiently constructing a huge number of structurally diverse chiral architectures with high optical purity. Based on the deep insights in the active modes and reaction mechanisms, new Brpnsted acid catalysts and... 

This chapter documents advances in the use of catalysis for regioselective transformations of carbohydrate derivatives. For this discussion, the catalysts are grouped into broad structural or functional classes (Lewis bases, Brpnsted acids, Lewis acids, transition metals). Processes that make use of enzyme catalysis (chemoenzymatic methods or metaboUc engineering) are not discussed here [8-10]. Emphasis is placed oti recent results that were not discussed in previous reviews on this and related topics [11—13]. 

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