Lithium shifts

In the rechargeable lithium-ion batteries, in which current-generating reactions are based on a "rocking chair" mechanism, the ions of lithium shift back and forth between the intercalation hosts of the cathode and anode. The... 

This is consistent with the relative ease of dissociation of poly(styryl)lithium in the presence of bases and also with the concentration dependence of enthalpy versus R plot (Fig. 4) with a break observed at an R value of ca. 1.0. These calorimetric results are also in agreement with the stoichiometric dependencies observed by Helary and Fontanille 92> from their kinetic and spectroscopic studies. For example, they reported that the UV wavelength of maximum absorption of poly(styryl)lithium shifted upon additions of TMEDA until an R value of 1.0 and then was constant. They also observed that TMEDA additions increased or decreased the rate of polymerization, depending on [PSLi] the increase or decrease in the rate leveled off at an R value of ca. 1.0. All... 

It is not surprising that it is difficult to insert lithium between parallel layers which are randomly stacked. When lithium intercalates between AB stacked layers, a shift to AA stacking occurs [26]. It is likely that the turbostratically stacked layers are pinned by defects (which can only be removed near 2300°C ) preventing the rotation or translation to AA stacking. Thus, we can understand why varies as 372(1-P), the fraction of layers with AB registered stacking. More studies of the details of the voltage profiles in Fig. 7 can be found elsewhere [6,7,27]. 

Fig. 25. Voltage versus capacity for the second discharge and charge of cells with lithium anodes and with cathodes made of Br-series samples. The curves have been sequentially offset for clarity. The shifts are Br700, 4.0V BrS OO, 3 OV Br900, 2 OV BrlOOO, l.OV, and BrllOO, 0.0V.

Most other studies have indicated considerably more complex behavior. The rate data for reaction of 3-methyl-l-phenylbutanone with 5-butyllithium or n-butyllithium in cyclohexane can be fit to a mechanism involving product formation both through a complex of the ketone with alkyllithium aggregate and by reaction with dissociated alkyllithium. Evidence for the initial formation of a complex can be observed in the form of a shift in the carbonyl absorption band in the IR spectrum. Complex formation presumably involves a Lewis acid-Lewis base interaction between the carbonyl oxygen and lithium ions in the alkyllithium cluster. 

Various other observations of Krapcho and Bothner-By are accommodated by the radical-anion reduction mechanism. Thus, the position of the initial equilibrium [Eq. (3g)] would be expected to be determined by the reduction potential of the metal and the oxidation potential of the aromatic compound. In spite of small differences in their reduction potentials, lithium, sodium, potassium and calcium afford sufficiently high concentrations of the radical-anion so that all four metals can effect Birch reductions. The few compounds for which comparative data are available are reduced in nearly identical yields by the four metals. However, lithium ion can coordinate strongly with the radical-anion, unlike sodium and potassium ions, and consequently equilibrium (3g) for lithium is shifted considerably... 

The structure of LiTa02F2, as reported by Vlasse et al. [218], is similar to a ReC>3 type structure and consists of triple layers of octahedrons linked together through their vertexes. The layers are perpendicular to the c axis, and each layer is shifted, relative to the layer below, by half a cell in the direction (110). Lithium atoms are situated in the centers of the tetragonal pyramids (coordination number = 5). The other lithium atoms are statistically distributed along with tantalum atoms (coordination number = 6) at a ratio of 1 3. The sequence of the metal atoms in alternating layers is (Ta-Li) - Ta - (Ta-Li). Positions of oxygen and fluorine atoms were not determined. The main interatomic distances are (in A) Ta-(0, F) - 1.845-2.114 Li-(0, F) - 2.087-2.048 (O, F)-(0,F) - 2.717-2.844. 

Table 55 presents the results discussed above. Fluoride melts containing tantalum contain two types of complex ions, namely TaF6 and TaF72 . The equilibrium between the complexes depends on the concentration of fluoride ions in the system, but mostly upon the nature of the outer-sphere cations. The complex ionic structure of the melts can be adjusted by adding cations with a certain polarization potential. For instance, the presence of low polarization potential cations, such as cesium, leads primarily to the formation of TaF72 complexes, while the addition of cations with relatively high polarization potentials, such as lithium or sodium, shifts the equilibrium towards the formation of TaF6 ions. 

In an effort to make productive use of the undesired C-13 epimer, 100-/ , a process was developed to convert it into the desired isomer 100. To this end, reaction of the lactone enolate derived from 100-) with phenylselenenyl bromide produces an a-selenated lactone which can subsequently be converted to a,) -unsaturated lactone 148 through oxidative syn elimination (91 % overall yield). Interestingly, when 148 is treated sequentially with lithium bis(trimethylsilyl)amide and methanol, the double bond of the unsaturated lactone is shifted, the lactone ring is cleaved, and ) ,y-unsaturated methyl ester alcohol 149 is formed in 94% yield. In light of the constitution of compound 149, we were hopeful that a hydroxyl-directed hydrogenation52 of the trisubstituted double bond might proceed diastereoselectively in the desired direction In the event, however, hydrogenation of 149 in the presence of [Ir(COD)(py)P(Cy)3](PF6)53 produces an equimolar mixture of C-13 epimers in 80 % yield. Sequential methyl ester saponification and lactonization reactions then furnish a separable 1 1 mixture of lactones 100 and 100-) (72% overall yield from 149). 

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