Hydrogen schematic mechanism

Fig. 5.4. Schematic mechanism for enantioselective hydrogenation of methyl acetamidocinnamate (MAC) over a cationic ruthenium catalyst. Reproduced...

Fig. 25. Schematic diagram indicating a possible hydrogen diffusion mechanism, by which (a) the hydrogen leaves a Si—H bond for an interstitial position, (b) inserts into a strained Si—Si bond, (c) returns to an interstitial position, and (d) passivates a pre-existing dangling bond (Kakalios and Jackson, 1988). 

Scheme 20.3 Schematic representation of the two different hydrogen transfer mechanisms (D = donor molecule ...

Figure 5.35 Schematic mechanism for the hydrogen desorption of NaAIH4. The catalyst permits the transfer of the two H ions to form the hexahydride.

Fig. 2.21. Schematic diagram of the possible hydrogen diffusion mechanism (a) the potential wells corresponding to the trapping sites and the energy of the mobile hydrogen b) the motion of the hydrogen through the Si—Si bonds.

Hydrogen adsorption on MgO can, in principle, be either molecular or dissociative. Dissociative adsorption of hydrogen on high-surface-area MgO has already been reported, and both homolytic and heterolytic pathways have been proposed 12). Homolytic splitting is supposed to operate under UV-irradiation only (117-119) and is not discussed further here. Heterolytic splitting takes place in the dark and at 300 K on coordinatively unsaturated (cus) Mg O surface pairs following the schematic mechanism illustrated in Scheme 2. 

E2S.15 Two observations must be explained in this catalytic deuteration of C-H bonds. The first is that ethyl groups are deuterated before methyl groups. The second observation is that a given ethyl group is completely deuterated before another one incorporates any deuterium. Let s consider the first observation first. The mechanism of deuterium exchange is probably related to the reverse of the last two reactions in Figure 26.20, which shows a schematic mechanism for the hydrogenation of an olefin by D2. The steps necessary for deuterium substitution into an alkane are shown below and include the dissociative chemisorption of an R-H bond, the dissociative chemisorption of D2, and the dissociation of R-D. This can occur many times with the same alkane molecule to effect complete deuteration. 

A schematic hydrogen absorption mechanism consists in the following three steps ... 

Figure 14.1. Hydrogen exchange mechanisms (a) Amide exchange at neutrai pH invoives base cataiyzed proton abstraction and acid cataiyzed transfer of deuterium from solvent. Measurable isotope effects on the amide hydrogen and a lack of a solvent isotope effect indicate that proton abstraction is rate limiting [1]. (b) Schematic diagram of the two-state model for hydrogen exchange in native proteins and kinetic prediction. The rate of...

Fig. 1 Schematic mechanism for photodynamics of ethylene on the tc 71 excited state. After photoexcitation, twisting and pyramidalization brings the molecule to an Sl/SO Cl, and further hydrogen migration creates ethylidene...

Figure 7 Schematic of various reactions at crack tip associated with hydrogen embrittlement mechanisms in aqueous environments. (From Ref 45.)...

Figure 4.1 Schematic mechanism of hydrogen permeation in dense Pd-based membranes.

Fig. 5.5 Schematic mechanism for asymmetric catalytic hydrogenation. The stereochemistry of the preferred intermediate (K q > K q) does not govern that of the preferred product (k k)...

Schematic of various reactions at crack tip associated with hydrogen embrittlement mechanisms in aqueous environments. (From Ford, F.P., The crack tip system it s relevance to the prediction of cracking in aqueous environments, in Proceedings of First International Conference on Environmentally Assisted Cracking of Metals, Kohler, WI, October 2-7,1988, Eds. R. Gangloff and B. Ives, Published by NACE, pp. 139-165.)...

Figure 12. Top Schematic model showing the mechanism of lithium storage in hydrogen containing carbons as proposed in Ref. [2471. Below Schematic charge/discharge curve of a hydrogen containing carbon.

Fig. 3.4 Schematic drawings illustrating the nucleation of silica precursor and possible mechanisms of reactions leading to silica formation. (A) The precursor hydrolysis. THEOS nucleates on a polysaccharide macromolecule through hydrogen bonds that are formed with hydroxy groups in the biomacromolecule. Per-...

The growth mechanism for the IF-MS2 (M = Mo,W) materials by the sulfidi-zation of the respective oxide nanoparticles has been studied in detail (12, 31). The growth mechanism is schematically illustrated in Fig. 4 (31a). Here oxide nanoparticles are sulfidized on the surface at temperatures between 800 and 950 °C in an almost instantaneous reaction. Once the first sulfide layer enfolds the oxide nanoparticle its surface is completely passivated, and hence sintering of the nanoparticles is avoided. In the next step, which may last a few minutes, reduction of the oxide nanoparticle core by hydrogen takes place. In the third step, which is rather slow and may take a few hours, depending on the size of the nanoparticles... 

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