Catalytic mechanism hydrogen exchange

The present article is a review of tt complex adsorption which has recently been proposed in catalytic reaction mechanisms (2-11). The main evidence for this intermediate has been obtained from isotopic hydrogen exchange reactions with aromatic compounds where an interpretation according to classical theories has met with increasing difficulties. The limitations of the classical associative and dissociative exchange mechanisms originally proposed by Horiuti and Polanyi (12) and Farkas and Farkas (13-15) re discussed. This is followed by a... 

In this volume the editors are presenting a set of what they believe are recent outstanding developments which concentrate heavily on mechanisms involved in several different classes of catalytic reactions Isomerization of olefins (M. Orchin), dehydration of alcohols (H. Pines and J. Manassen), hydrogen exchange (J. L. Garnett and W. A. Sollich-Baumgartner), and hydrogenation of unsaturated hy-... 

Intra- and intermolecular hydrogen transfer processes are important in a wide variety of chemical processes, ranging from free radical reactions (which make up the foundation of radiation chemistry) and tautomeriza-tion in the ground and excited states (a fundamental photochemical process) to bulk and surface diffusion (critical for heterogeneous catalytic processes). The exchange reaction H2 + H has always been the preeminent model for testing basic concepts of chemical dynamics theory because it is amenable to carrying out exact three-dimensional fully quantum mechanical calculations. This reaction is now studied in low-temperature solids as well. 

ATP to yield the d isomer of methylmalonyl CoA (Figure 22.11). This carboxylation reaction is catalyzed by propionyl CoA carboxylase, a biotin enzyme that is homologous to and has a catalytic mechanism like that of pyruvate carboxylase (Section 16.3.2). The d isomer of methylmalonyl CoA is racemized to the 1 isomer, the substrate for a mutase that converts it into succinyl CoA by an intramolecular rearrangement. The -CO-S-CoA group migrates from C-2 to C-3 in exchange for a hydrogen atom. This very unusual isomerization is catalyzed by methylmalonyl CoA mutase, which contains a derivative of vitamin Bj2, cobalamin, as its coenzyme. 

---