Stability of Anionic Intermediates

It is believed that base-catalyzed reactions occur through carbanionic intermediates. Thus, from a mechanistic viewpoint, which may also help to design better catalysts, 

The ability of a solvent to stabilize a carbanion depends on its ability to disperse the negative charge through hydrogen bonding and charge transfer. Thus, depending on the effect desired, one should find the appropriate solvent for the reaction. 

Furthermore, a catalyst can stabilize a carbanion not only through a stronger or weaker basicity of the site but by means of its coordination with the conjugated surface Lewis acid. It is apparent that the interplay between the acid and base pair can markedly help in the control of selectivity. 

Catalytic Activity of Aikaiine Earth Metai Oxides 

Alkaline earth metal oxides have been used as solid base catalysts for a variety of organic transformations. Excellent reviews by Tanabe 4) and Hattori 2,3,7) provide detailed information about the catalytic behavior of alkaline earth metal oxides for several organic reactions of importance for industrial organic synthesis. In this section, we describe in detail reactions that have been reported recently to be catalyzed by alkaline earth metal oxides. 

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Most of the isomerizations mentioned above are catalyzed by solid acids and bases. In the case of solid acids the reactions proceed via classical or non-classical carboca-tions and the stabilities of the reaction intermediates are generally very important in determining rate and selectivity. For base catalysis the stability of anionic intermediates is important. 

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