Clusters acide-base reactions

Solvation Ultrafast Dynamics of Reactions VIII. Acid-Base Reactions in Finite-Size Clusters of Naphthol in Ammonia, Water, and Piperidine, S. K. Kim, J. J. Breen, D. M. Willberg, L. W. Peng, A. Heikal, J. A. Syage, and A. H. Zewail, J. Phys. Chem. 99, 7421 (1995). 

Both experiments and theory join in the studies of hydrogen transfer reactions. In general, the approach is of two categories. The first involves the study of prototypical but well-defined molecular systems, either under isolated (microscopic) conditions or in complexes or clusters (mesoscopic) vdth the solvent, in the gas phase or molecular beams. Such studies over the past three decades have provided unprecedented resolution of the elementary processes involved in isolated molecules and en route to the condensed phase. Examples include the discovery of a magic solvent number for acid-base reactions, the elucidation of motions involved in double proton transfer, and the dynamics of acid dissociation in finite-sized clusters. For these systems, theory is nearly quantitative, especially as more accurate electronic structure and molecular dynamics computations become available. 

Another class of chemical reactions also covered here is that of proton-transfer reactions. These processes play a key role in solution chemistry, and more specifically in acid—base reactions. In this class of reactions the cmcial step involves the motion of the hydrogen atom, which typically occurs on the picosecond or femtosecond time-scale. By investigating the time dynamics of these processes in size-selected clusters, for a given system, information is gained at which specific cluster size the onset of the proton transfer reaction occurs. 

The rich variety of active sites that can be present in zeolites (i) protonic acidic sites, which catalyze acid reactions (ii) Lewis-acid sites, which often act in association with basic sites (acid-base catalysis) (iii) basic sites (iv) redox sites, incorporated either in the zeolite framework (e.g., Ti of titanosHicates) or in the channels or cages (e.g., Pt clusters, metal complexes). Moreover, redox and acidic or basic sites can act in a concerted way for catalyzing bifunctional processes. 

For both reactions the yields of the enethiolate ions are better than 95% small amounts of HF7V thioenolate cluster ions were also observed182,183. The results of some acid-base and exchange chemical studies of enethiolate anions are summarized in Table 25. 

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