Catalysis and Reaction Mechanism

Another method of increasing the reaction rate is by employing a catalyst. A catalyst is a substance that speeds up the reaction but is not consumed in the reaction. A substance that slows down or stops a reaction in known as an inhibitor. To understand how catalysts work and their role in reaction kinetics requires knowledge of reaction mechanisms. A reaction mechanism is the series of reactions or steps involved in the conversion of reactant to 

According to this reaction, ozone, O3, combines with atomic oxygen to produce molecular oxygen. One mechanism to explain this reaction is 

The reaction mechanism shown for ozone depletion includes chorine. Chlorine in this reaction acts as a catalyst. A principal source of this chlorine is from the ultraviolet breakdown of CFC (chlorofluorocar- 

In the decomposition of hydrogen peroxide, the iodide catalyst reacts in the first elementary step, and it is regenerated in the second step. 

In a reaction mechanism with two or more steps, the slowest step will control the rate of the net reaction. This step is referred to as the rate determining step. The rate determining step in a reaction mechanism can be compared to the slowest step in a series of activities. For example, say we were mailing out letters and set up an assembly line of several people that included the following tasks 1) take envelope out of box, 2) place stamp on envelope, 3) put letter in envelope, 4) address envelope, and 5) seal envelope. All the steps except step 4 could be done in a matter of seconds. It might take a minute or two to 

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Dedieu A (1999) Theoretical Treatment of Organometallic Reaction Mechanisms and Catalysis. 4 69-107... 

Dedieu, A. Theoretical treatment of organometallic reaction mechanisms and catalysis. Top. Organomet. Chem. 1999,4, 69-107. 

Electron paramagnetic resonance (EPR) spectroscopy [1-3] is the most selective, best resolved, and a highly sensitive spectroscopy for the characterization of species that contain unpaired electrons. After the first experiments by Zavoisky in 1944 [4] mainly continuous-wave (CW) techniques in the X-band frequency range (9-10 GHz) were developed and applied to organic free radicals, transition metal complexes, and rare earth ions. Many of these applications were related to reaction mechanisms and catalysis, as species with unpaired electrons are inherently unstable and thus reactive. This period culminated in the 1970s, when CW EPR had become a routine technique in these fields. The best resolution for the hyperfine couplings between the unaired electron and nuclei in the vicinity was obtained with CW electron nuclear double resonance (ENDOR) techniques [5]. 

CHAPTER 12 ORGANOTRANSITION METAL REACTION MECHANISMS AND CATALYSIS... 

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