Activation energies, lithium

Therefore, the temperature dependence of the conductivity of complexes (LiX)o, igy/MEEP (X=CF3C00, SCN, SO3CF3, BF4) were also compared. The highest conductivity was obtained with BF4, and the activation energies for ion transport were found to be similar, suggesting that the mechanism for ion motion is independent on the salt. The lithium transport number, which varies from 0.3 to 0.6, depending on the complexed salt, does not change with concentration. 

TScc is also the stage at which the enantiofacial selectivity of the reaction is determined [80]. This conflicts with the conventional assumption that the face selectivity is established in the initial Ti-complexation [40a], which is now shown to represent a preequilibrium state preceding TScc. The calculated activation energy taking the solvation of the lithium atoms into account shows reasonable agreement with recently determined experimental data [75]. 

TABLE 6. Computed reaction and activation energies and corresponding isotope effects for the sequence of reactions between lithium vinyloxide (LiEn) and formaldehyde and between the hthium enolate of acetone (AcCH2Li) and acetaldehyde. Reproduced with permission from Reference 29. Copyright 1998 American Chemical Society... 

In homopolymerization initiated by sec-butyl-lithium in hexane, isoprene is a more active monomer than butadiene (with kj 5.53 x 10-5 sec l vs. ki 0.98 x 10 sec- at 20eC). This is also true for reactions at 30° and 40°C. The apparent activation energy for both monomers has been found to be roughly the same,... 

The polaron radius, if greater than (2), will be very sensitive to m —or, more exactly, to the bandwidth of the undistorted lattice. A particularly striking effect is that in materials like NiO doped with lithium, where the carriers are Ni3 + ions and in which the hole moves from one Ni2+ ion to another. The mass enhancement for a free carrier is rather small (about 5), while a bound carrier hopping round the Li+ ion on the sites available to it behaves like a small polaron with an activation energy for motion (see Bosman and van Daal (1970) and Chapter 6 below). 

Transition structures for the lithium-bromine exchange reaction of 1,1-dibromo-alkenes with methyllithium have been located by both the B3LYP and the MP2 levels of theory with the 6-31+G basis set.67 The reaction with methyllithium dimer gave similar results with lower activation energies. These calculations predict both the kinetic and the thermodynamic stereoselectivity correctly. It has been found that predominantly the sterically more constrained bromine atom of 1,1-dibromoalkenes reacted with alkyllithium (dimer) in the kinetic condition. 

If the elimination of hydride ion is rate-determining and it is assumed that the addition step is rapidly reversible, the results might be explained as follows (Scheme IV), taking 3-picoline as an example The aromatization step in Scheme IV probably involves the abstraction by the lithium cation of the hydrogen atom with its bonding pair of electrons, so that an electron-repelling ortAo-methyl should lower the activation energy of such a process more than a para-methyl... 

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