Mechanism of chemical transformation

Raja Ram, J. and Kuriacose, J.C. Kinetics and Mechanism of Chemical Transformations, 1st Edition, McMillan India Ltd., New Delhi (1993). 

Schenck sensitization mechanism The mechanism of chemical transformation of one molecular entity caused by photoexcitation of a sensitizer which undergoes temporary covalent bond formation with the molecular entity. 

Chemical kinetics resembles (in some sense) classical mechanics, which allows the final state of the dynamic systems to be accurately predicted when dynamic equations are known for describing the time behavior of the system and exact starting conditions are given. On the other hand, in complex kinetic schemes, the final result of the transformations under consideration is expected to change considerably depending on the partic ular assumptions about elementary steps of the process and the choice of the kinetic scheme, as well as on the assumptions, rather arbitrary some times, about reversibility of each of these steps. This makes it difficult to describe the time evolution of the systems with poorly understood or complex mechanisms of chemical transformations. 

The application of combinations of electrochemical methods with non-electro-chemical techniques, especially spectroelectrochemistiy (UV-VIS, FITR, ESR), the electrochemical quartz crystal microbalance (EQCM), radiotracer methods, probe beam deflection (PBD), various microscopies (STM, AFM, SECM), ellipsometiy, and in situ conductivity measurements, has enhanced our understanding of the nature of charge transport and charge transfer processes, stmcture-property relationships, and the mechanisms of chemical transformations that occur during charg-ing/discharging processes. 

So far, when stating the value approaeh for the eontrol of chemical reactions it was assumed that a researcher has enough information on the detailed mechanism of chemical transformation. Meanwhile, often the data on the reaetion mechanism are incomplete, including those for commercially implemented proeesses. In such cases one has to rely upon empirical methods. As applied to complex ehemical reactions, the empirical approaches are the subject of special discussion (see for example [42]). Here, on the basis of the available data, only some ideas about the basic principles of empirical modeling are presented. 

Imagine that an additional component, C, takes part in the reaction. In this case, the answer to the question of whether it is possible to overshoot the equilibrium is Yes However, then another question arises How much can this equilibrium be overshot Let us assume that A, B, and C are isomers again and that at equilibrium their amounts are equal (each 33% of the total amount). Also assume that all transformations are possible (so A can be converted to B and to C, B to A and C, and C to A and B). For this system overshooting of the equilibrium is possible, provided that there are no limitations on the detailed mechanism of chemical transformations. Then, if the reactor initially contains 100% A, the concentration of B may overshoot its equilibrium concentration, but may not exceed a certain boundary ( 77% of the total amount). 

For completeness, one can mention that others local descriptors have been designed over the years (ellipticity, various density energies like the and kinetic, potential V Hamiltonian ones at BCP, reduced density gradient variation rates [98], DFT-based local descriptors [99]...)- Besides, following the appearance and disappearance of critical points also constitutes an efficient way of describing the mechanism of chemical transformations (see Ref. [100] for a recent example). 

This chapter logically presents the mechanism of chemical transformation of the fly ash into zeolites. Attempts have been made to highlight the effects of alkali activation on the overall characteristics of the fly ash. Also, a need to innovate novel methods of synthesis of the fly ash zeolites, and to improve their overall characteristics, has been the main focus of this chapter. In addition, the chapter presents details of die applications of various advanced characterization tools (viz., physico-chemical, mineralogical and morphological) for exploring the overall properties of the zeolites. 

The interaction between experiment and theory is very important in the field of chemical transformations. In 1981 Kenichi Fukui and Roald Hoffmann received a Nobel Prize for their theoretical work on the electronic basis of reaction mechanisms for a number of important reaction types. Theory has also been influential in guiding experimental work toward demonstrating the mechanisms of one of the simplest classes of reactions, electron transfer (movement of an electron from one place to another). Henry Taube received a Nobel prize in 1983 for his studies of electron transfer in inorganic chemistry, and Rudolf Marcus received a Nobel Prize in 1992 for his theoretical work in this area. The state of development of chemical reaction theory is now sufficiently advanced that it can begin to guide the invention of new transformations by synthetic chemists. 

Actual catalysis is a chemical phenomenon, since the intimate mechanisms of catalytic transformations are determined by chemical interaction of reagents with the catalyst, atomic structure, and the energy of formed intermediate active complexes [5], It obviously is the world of molecular chemistry of the interface phenomena, kinetics, and mechanisms of catalytic transformations at a molecular level. 

J. Brange, Chemical Stability of Insulin. 4. Mechanisms and Kinetics of Chemical Transformations in Pharmaceutical Formulation , Acta Pharm. Nordica 1992, 4, 209-222. 

Understanding Mechanisms of Metabolic Transformations as a Tool for Designing Safer Chemicals... 

The chemical change in which molecules of methane and oxygen transform to molecules of carbon dioxide and water as atoms break old bonds and form new ones. The actual mechanism of this transformation is more complicated than depicted here however, the idea chat new materials are formed by the rearrangement of atoms is accurate. 

---