Intrinsic energy barrier

One of the reasons for the quite high intrinsic energy barrier (X/4 ca... 

The above model has been further explored to account for reaction efficiencies in terms of a scheme where nucleophilicities and leaving group abilities can be rationalized by a structure-reactivity pattern. Pellerite and Brau-man (1980, 1983) have proposed that the central energy barrier for an exothermic reaction (see Fig. 3) can be analysed in terms of a thermodynamic driving force, due to the exothermicity of the reaction, and an intrinsic energy barrier. The separation between these two components has been carried out by extending to SN2 reactions the theory developed by Marcus for electron transfer reactions in solutions (Marcus, 1964). While the validity of the Marcus theory to atom and group transfer is open to criticism, the basic assumption of the proposed model is that the intrinsic barrier of reaction (38)... 

This approach yields a series of intrinsic energy barriers for the SN2 selfexchange reactions which vary widely depending on the vibrational frequencies assumed for the transition states. Nevertheless, the numbers derived for a given model can be used to establish some interesting conclusions. For example, chloride- and bromide-exchange reactions display an E 0... 

According to this definition, the intrinsic energy barrier (pi represents the minimum energy required for the charge injection from the metal into the polymer molecule, which is a constant for a given polymer and metal pair. On the other hand, the contact-dependent component A

metal/polymer interface, which is morphology dependent. 

Where the excited state solute or probe molecule has. In competition with phosphorescence, an efficient nonradlatlve decay path which Involves rotational motion of the carbon skeleton. It might be expected that there will exist an Intrinsic energy barrier to this rotation. Provision of sufficient thermal energy to overcome the barrier would thus enhance nonradlatlve decay at the expense of phosphorescence. This Is a purely Intramolecular property of the probe molecule and Is entirely Independent of the environment. 

This is caused by dispersion interaction between the carbon atoms of the reactant and the oxygen atoms of the zeolite framework. Interaction of the reactants with the Brpnsted acid site further reduces the potential. The intrinsic energy barrier for the forward reaction is the difference between the bottom of the well for the coadsorption of A and B at the active site and the top of the transition state. First, the... 

Hydride transfer reactions have a high intrinsic energy barrier (eq(46)), because n is reasonably low (=0.5). This becomes obvious when one writes. 

Marcus showed that if within a log k — log X relationship variations in the rate constant solely reflect changes in the equilibrium constant, then log k, or in Marcus s formulation the free energy of activation AG may be expressed in terms of a free energy of the proton-transfer step of the reaction AGr, and an intrinsic energy barrier to proton-transfer for reaction of a substrate and. acid for which AGg = 0 ... 

In Marcus s treatment the variation of isotope effects is represented by supposing that isotopic reactants differ only in their intrinsic energy barriers Ah and Ad- Replacement of AG in equation 35 by — In klikT/h)] then gives ... 

Total energy Electron density Eermi energy Electron d band—orbital Transfer coefficient Intrinsic energy barrier Covalent binding Anti-ligands... 

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