Through-Shell Reactions

Through-Shell Reactions 9.4.1 Proton Transfer Reactions... 

Robbins, T. A., Cram, D. J., Through-shell oxidation and reduction reactions of guests in a hollow container single-molecule. 

Ans. The most stable elements are the noble gases. Their stability is based on the fact that they have filled outer (valence) shells. All the other elements have an unfilled outer valence shell and are therefore unstable. They can achieve the same stability by filling their valence shells with the appropriate number of electrons. This is achieved through chemical reaction and consequent chemical bond formation. Therefore, the principal driving force for the formation of chemical bonds is that most elements are inherently unstable. 

Figure 24.2a shows a design consisting of a permselective membrane tube placed coaxially inside an outer shell. Reaction occurs in the inner tube which is filled with catalyst. One (or more) of the products from the inner tube permeates through the catalytically inert membrane wall into the outer shell where it is swept away by an inert gas (usually argon). When the catalyst is a packed bed as shown in Figure 24.2a, the reactor is designated as a packed-bed inert selective membrane reactor (IMR-P). 

Figure 1. Representative slice through the reaction hypersurface for deuterium exchange for a reactant with an unfilled valence shell, showing the binding energy of the intermediate and the reaction exoergicity. ...

Organic chemists led the way in picturing molecular bonding. They relied on such concepts as radicals (which kept their identity through various reactions) and atoms with a fixed valence or combining power. Once the electron was discovered in the early part of the twentieth century, Lewis was able to explain some aspects of bonding on the basis of his electron-dot formulas and the octet mle. The valence-shell electron-pair repulsion (VSEPR), valence-bond (VB), and molecular orbital (MO) theories followed in the 1930s. 

Metal ions in water, commonly denoted exist in numerous forms. Despite what the formula implies, a bare metal ion, Mg for example, cannot exist as a separate entity in water. To secure the highest stability of their outer electron shells, metal ions in water are bonded, or coordinated, to water molecules in forms such as the hydrated metal cation M(H20)x , or other stronger bases (electron-donor partners) that might be present. Metal ions in aqueous solution seek to reach a state of maximum stability through chemical reactions including acid-base. 

To overcome this voltage restriction, TiC/C-Si core-shell NWs utilize an inert TiC/C scaffold (Fig. 1.33a,b) so that charging can occur down to low potentials, for example, 10 mV vs. Li/Li, in order to fully lithiate the Si shell. TiC/C nanofibers were S5mthesized through thermochemical reaction of a titanium alloy (Ti 6A1-4V) foil in acetone vapor at 850°C. Detailed TEM analysis showed that the nanofibers consisted of a 30 nm crystalline TiC core coated with a 20-40 nm amorphous carbon shell (Fig. 1.33c). Cyclic voltammetry on... 

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