Carbonyl groups, 40. elimination surface

The carbonyl group, C=0, is perhaps the most important functional group in organic chemistry. If we replace one of the carbons in our elimination surface with an oxygen atom, we get a related surface, shown in Figure 4.28. 

The introduction of an >-substituent (CN, Cl, or OH) into a primary n-alkyl chloride considerably enhances the rate of 5 n2 chloride exchange in the gas phase. Reactivity trends suggest that the acceleration is due primarily to through-space solvation of the transition state, especially charge-dipole interactions. Potential-energy surfaces are discussed. In further work by the same group, the translational energy dependence of the rate constants of several gas-phase 5 n2 and carbonyl addition-elimination reactions has been measured by FT-ICR spectroscopy. The results were interpreted by RRKM calculations. 

Zinc and hydrochloric acid is able to reduce certain carbonyl groups to methylene. The oxygen is believed to be eliminated as water from a partially reduced intermediate bound to zinc. This reaction is known as the Clemmensen reduction. The corresponding alcohols are not reduced to hydrocarbons under the conditions of the reactions, so they obviously cannot be intermediates in the overall process. The mechanism of the reaction is not known in detail. Formation of carbon-zinc bonds at the metal surface may be involved. 

Attempts have been made to mimic proposed steps in catalysis at a platinum metal surface using well-characterized binuclear platinum complexes. A series of such complexes, stabilized by bridging bis(diphenyl-phosphino)methane ligands, has been prepared and structurally characterized. Included are diplati-num(I) complexes with Pt-Pt bonds, complexes with bridging hydride, carbonyl or methylene groups, and binuclear methylplatinum complexes. Reactions of these complexes have been studied and new binuclear oxidative addition and reductive elimination reactions, and a new catalyst for the water gas shift reaction have been discovered. 

The surface chemistry of a carbon is known to play a crucial role in many applications, most notably in adsorption and catalysis [91-94]. It has been observed that the surface of templated porous carbons mainly has oxygen-containing functional groups, such as carboxyl, carbonyl, quinone, and hydroxyl [76,94,95]. Such groups, especially the carboxyls, can be eliminated by high-temperature... 

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