Activation barriers intermolecular

The solution phase is modeled explicitly by the sequential addition of solution molecules in order to completely fill the vacuum region that separates repeated metal slabs (Fig. 4.2a) up to the known density of the solution. The inclusion of explicit solvent molecules allow us to directly follow the influence of specific intermolecular interactions (e.g., hydrogen bonding in aqueous systems or electron polarization of the metal surface) that influence the binding energies of different intermediates and the reaction energies and activation barriers for specific elementary steps. 

On the other hand, fluorine substitution at both ortho positions (21a) raises the CASPT2/6-31G barrier from 8.6 to 13.0 kcal mol The increase in the barrier height inhibits the rearrangement reaction and allows 21a to participate in intermolecular chemistry. Subsequent experiments determined that its activation barrier is 7.3-8.0 kcal mol (depending on the solvent). Calculations predict a... 

A homogeneous chemical reaction proceeds via transport processes (convection, diffusion) approach of the reactants due to intermolecular forces in the 100 pm range leads to molecular complexes and finally, after activation of the complex, charge and bond redistribution takes place. Matrix techniques offer the possibility of studying individual stages in a reaction process between isolated species. The efficiency of a reaction in a matrix depends on the mobility of the matrix-isolated species, the strength of the intermolecular interaction, and the height of the activation barrier. The mobility of a species which is isolated in a matrix is related to its size electrons and atoms are far more mobile... 

Intermolecular hydroamination of alkynes, which is a process with a relatively low activation barrier, has not been used for the synthesis of chiral amines, since the achiral Schiff base is a major reaction product. However, protected aminoalkynes may undergo an interesting intramolecular allylic cyclization using a palladium catalyst with a chiral norbomene based diphosphine ligand (Eq. 11.9) [115]. Unfor tunately, significantly higher catalyst loadings were required to achieve better enantioselectivities of up to 91% ee. 

The latter step of intermolecular C-N bond formation was independently investigated within the development of a palladium(II)/palladium(IV) catalysis for C-H bond activation and amidation (Figure 16.8) [127]. Theoretical support from calculations at the LANL2DZ level show that a palladium(lV) species is generated from the oxidation of palladium(II) chelate 188 with NFSI, which does not form a neutral palladium(IV) intermediate, but rather engages in direct nucleophilic attack of the bissulfonimide anion at the methylene position next to the electrophilic palladium(I V) center. This step proceeds with an activation barrier... 

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