Ketones factors influencing acidity

Rules 1 and 2 may be accepted as a generalization based primarily on the results obtained over platinum catalysts. However, there have been known many examples of the exception to this rule,153 since the stereochemistry of hydrogenation may be influenced by many factors, such as the solvent, the temperature, the hydrogen pressure, and the basic or acidic impurity associated with catalyst preparation, as well as the activity of the catalyst, and since the effects of these factors may differ sensitively with the catalyst employed and by the structure of the ketone hydrogenated. 

Most PAHs in the atmosphere are associated with particulates (Baek et al. 1991). Vu-Duc and Huynh (1991) describe two types of chemical reactions that appear to be the predominant mode of transformation of these PAHs (1) reactions between PAHs adsorbed on the particle surfaces and oxidant gases like NO2, O, and SO3 that do not appear to be influenced by exposure to UV irradiation and (2) photooxidation of PAHs irradiated either under solar radiation or simulated sunlight which produces a variety of oxidized derivatives such as quinones, ketones, or acids. Kamens et al. (1990) estimate that, even in highly polluted air, photolysis is the most important factor in the decay of particle-sorbed PAHs in the atmosphere, followed by reaction with NO2, N2O5, and HNO3. 

Both the efficiency and the stereochemical course of the hydrogenation of a,/S-unsaturated ketones are strongly influenced by the experimental factors, particularly the nature of the solvent and the acidity or basicity of the reaction mixture. It is usually difhcult to predict the product distribution in a particular reaction under a given set of conditions. Some efforts have been made to rationalize the effect of the various parameters on the relative proportions of the 1,2- to 1,4-addition products, as well as on the stereochemistry of the reduction. ... 

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