Protons in Oxides

Norby, T. and Earring, Y. (1997) Concentration and transport of protons in oxides. Curr. Opin. Solid State Mater. Sci., 2, 593-9. 

A proper treatment of the dissolution of water and defect chemistry of protons in oxides was first given by Stotz and Wagner (1967). Later on, Norby (1987) and others have given extended treatments of hydrogen defect equilibria, and Kreuer (1996) has reviewed protons in materials in general. 

The free transport is the principal mode of transport of protons in oxides, and in this mechanism protons jump from one oxygen ion to a neighbouring one. After each jump the proton in the hydroxide rotates such that the proton reorients in the electron cloud and becomes aligned for the next jump. This is illustrated schematically in Fig.5.11. The rotation and reorientation is believed to involve a small activation energy and the jump itself is considered to be the ratedetermining step. 

Eq. 5.55 still holds for interstitial diffusion of a dilute solution of an interstitially dissolved solute, such as light elements (H, C etc. in metals or protons in oxides), but in this case the number of solute atoms or ions and the number of defects is of course the same, so that in these cases the diffusion coefficient for the solute and for the (interstitial) defects is the same. 

Proton Conductivity in Acceptor-Doped Perovskites 11.2.1 Protons in Oxides... 

Poly(methyl vinyl ether) [34465-52-6] because of its water solubility, continues to generate commercial interest. It is soluble in all proportions and exhibits a well-defined cloud point of 33°C. Like other polybases, ie, polymers capable of accepting acidic protons, such as poly(ethylene oxide) and poly(vinyl pyrroHdone), each monomer unit can accept a proton in the presence of large anions, such as anionic surfactants, Hl, or polyacids, to form a wide variety of complexes. 

Acids are poor catalysts for ring cleavage of thiirane 1,1-dioxides but are good catalysts for reactions of thiirane 1-oxides with nucleophiles. These reactions of episulfoxides are believed to proceed by protonation of the oxygen atom (but see the NMR evidence cited above for 5-protonation in fluorosulfonic acid) and will be treated in the section on nucleophilic reactions. 

Amine oxides, prepared to protect tertiary amines during methylation and to prevent their protonation in diazotized aminopyridines, can be cleaved by reduction (e.g., SO2/H2O, 1 h, 22°, 63% yield H2/Pd-C, AcOH, AC2O, 7 h, 91% yield Zn/HCl, 30% yield). Photolytic reduction of an aromatic amine oxide has been reported [i.e., 4-nitropyridine A-oxide, 300 nm, (MeO)3PO/CH2Cl2, 15 min, 85-95% yieldl. ... 

Complete exchange of protons in a sterically unhindered position a to a carbonyl group can be achieved by heating a solution of the ketone in O-deuterated solvents in the presence of an acid or base catalyst, the latter being the more effective. The most commonly used solvents are methanol-OD, ethanol-OD, and the aprotic solvent anhydrous tetrahydrofuran or dioxane mixed with deuterium oxide. Under alkaline conditions the exchange rate in 153 2 14,164 stcroids, for example, is usually... 

Epoxides are unusual in that the protons on the ring are more shielded than expected. The protons in ethylene oxide, for exanple, appear at 8 2.5 instead of the 8 3.2-4.0 range just cited for dialkyl ethers. 

The product of nucleophilic attack can be anticipated by examining the lowest-unoccupied molecular orbital (LUMO) on protonated cyclopentene oxide. From which direction (top or bottom) would a nucleophile be more likely to approach each epoxide carbon in order to transfer electrons into this orbital Explain. Does one carbon contribute more to the LUMO, or is the orbital evenly spread out over both epoxide carbons Assuming that LUMO shape dictates product stereochemistry, predict which stereoisomers will be obtained, and their approximate relative amounts. Is the anticipated kinetic product also the thermodynamic product (Compare energies of 1,2-cyclopentanediol stereoisomers to tell.)... 

Chemical Shifts S of the Cyclic Protons in the h NMR Spectra of 1,2,4-Triazines AND Their W-Oxides in CDCI3 (A) or DMSO- Is (B) in Comparison (A ) with Those of the Parent 1, 2,4-Triazines... 

The NMR spectrum of methyl kasugaminide in deuterium oxide at 100 Me is shown in Figure 3. The anomeric proton at C-l linking with methoxyl group is shown as a doublet at 4.57 p.p.m. indicating one proton at C-2. The weak coupling, 1.6 c.p.s., is possible between protons in cis relation (28) or in equatorial-equatorial relation (6) at C-l and C-2 of the six-membered ring. 

The ESR spectrum of the thioxanthene S, S-dioxide radical anion itself shows that the two possible conformers coexist, since the two methylene protons are not equivalent. In the case of the 9-monoalkyl derivatives, the large coupling constant observed for the 9-proton leads to the conclusion that the 9-substituent is in the boat equatorial position as in II1 F Thus the radical anions and the neutral molecule display different conformations. The protons in the 9-position of the radical anions of cis-9-methylthioxanthene S-oxides (2, n — 1, R1 = H, R2 = CH3) have an appreciable coupling constant10 which suggests that these radical anions have the substituent in the pseudo-axial position. Furthermore, in the radical anions the S—O bond is pseudo-axial. These situations are exactly the opposite of that observed for the neutral compound. 

In general, corrosion of metal is always accompanied by dissolution of a metal and reduction of an oxidant such as a proton in acidic solution and dissolved oxygen in a neutral solution. That is, metal corrosion is not a single electrode reaction, but a complex reaction composed of the oxidation of metal atoms and the reduction of oxidants. 

Strong acids (the acids listed in Table J.l) are completely deprotonated in solution weak acids (most other acids) are not. Strong bases (the metal oxides and hydroxides listed in Table J.l) are completely protonated in solution. Weak bases (ammonia and its organic derivatives, the amines) are only partially protonated in solution. 

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