Oxygen transfer, rate-determining step

It is important to appreciate the role of the solvent in this transformation, removing and supplying protons, and to understand that tautomerism is not merely transfer of a proton from the a-carbon to the carbonyl oxygen. The rate-determining step in tautomerism will be removal of the a-hydrogen protonation of... 

Diffusion-limited rate control at high basicity may set in. This is more eommonly seen in a true Br nsted plot. If the rate-determining step is a proton transfer, and if this is diffusion controlled, then variation in base strength will not affect the rate of reaction. Thus, 3 may be zero at high basicity, whereas at low basicity a dependence on pK may be seen. ° Yang and Jencks ° show an example in the nucleophilic attack of aniline on methyl formate catalyzed by oxygen bases. 

A great deal of kinetie information on the AE reaetion has been obtained. The rate of reaetion is first order in allylie aleohol, Ti(0-iPr)2(tartrate), and TBHP. In addition, the rate is inversely-square dependent on isopropoxide. This refleets the required replaeement of two isopropoxide ligands on Ti(0-iPr)2(tartrate) with TBHP and the allylie aleohol. The rate-determining step is oxygen transfer from the peroxide to the olefin. 

In another possible mechanism, two NO2 molecules collide in the rate-determining step to form NO and NO3. In a second and faster step, the highly reactive NO3 intermediate transfers an oxygen atom to CO in a bimolecular collision ... 

The data reported and mechanism proposed permit no conclusions to be drawn concerning the products formed in the rate-determining step. According to the authors the reaction could occur by oxygen transfer, and no production of arsenic-(IV) would be required. 

In this case, direct electron transfer between the catalyst and O2 produces the superoxide radical (or other reduced forms of oxygen) which can be involved in a series of subsequent redox reactions. If these reactions are relatively fast, the rate determining step is Eq. (3) and the overall process can be interpreted in terms of relatively simple rate laws. 

There are two competing views as to the first adsorption step of the oxygen molecule. Following early propositions by Damjanovic [79,80], the rate-determining step of the ORR sequence starts with simultaneous charge and proton transfer to adsorbed oxygen molecules forming an 02H species adsorbed on the electrode metal atom M ... 

It must be emphasized again that these discussions on the conductivity of zinc oxide have been based on the two assumptions (1) that the chemisorption of oxygen has a strong effect on the resistance of the zinc oxide and (2) that the rate-determining step in the chemisorption of oxygen is an electron transfer. The former assumption has been based on indirect arguments, as well as on some direct experimental evidence. The latter assumption is based on the ability of the model to explain in a simple consistent manner the various experimental effects, some of which have been described, and some of which will be, in later chapters. 

They suggest that the rate determining step for the high temperature thermal decomposition is a proton-transfer on the surface of the solid followed by oxidation of the ammonia gas by radicals resulting from the decomposition of perchloric acid. It seems probable that perchloric acid should undergo fast decomposition at these temperatures, generating oxygen atoms which oxidize the ammonia ... 

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