Electrostatic interaction between various electron

In 1998, Yang and coworkers reported a series of (7 )-carvone derived ketones (63) containing a quaternary center at and various substituents at (Fig. 22) [119]. The ees of fran -stilbene oxide varied with different para and meta substituents when 63b was used as the catalyst. The major contribution for the observed ee difference is from the n-n electronic repulsion between the Cl atom of the catalyst and the phenyl group of the substrate. The substitution at also influences the epoxidation transition state via an electrostatic interaction between the polarized C -X bond and the phenyl ring on franx-stilbene (Table 6, entries 3-7, 10-14). In 2000, Solladie-Cavallo and coworkers reported a series of fluorinated carbocyclic ketones... 

Adsorptive purification of the type we are talking about here (sometimes called physisorptiori) involves a relatively weak interaction between the sorbate molecule and the surface active sites in the sorbent. The association depends mostly on van der Waals forces, which are primarily caused by electronic and/or electrostatic interactions between electron-rich or electron-poor regions of the sorbate molecule and receptive sites on the sorbent surface. Molecules bound by such weak forces can be removed by various solvent extraction techniques in contrast, molecules that actually form covalent bonds with the surface (chemisorption) usually cannot. 

These ionic and covalent bonds arise from the tendency of atoms to attain a stable configuration of electrons for each atom in a molecule, by either the transfer or the sharing of electrons between atoms. Because a molecule consists of at least two atoms with positively charges nuclei and negatively electronic clouds about these atoms, there are electrostatic interactions between the various particles of the atoms in the molecule. 

To understand the nature of the pH dependence of Lab on pH, we consider a simple phenomenological model in which we suppose only electrostatic interactions between reactants and in which only two amino acid residues, close to Qb, are involved in the proton uptake by RCs after the first flash. The two amino acids, designated here as D (i.e.. Asp) and E (i.e., Glu), generate four different protonation states DHEH, D-EH, DH E- and D E. Electrostatic interactions between amino acid residues and quinone acceptors give rise to different pKs and rate constants for the various ionization states of D and E and the charge states of Ae quinones. Instead of one state of the quinone acceptors, for example QaQb> it is necessary to consider four QaQb(DHEH), QaQb(D"EH), (JaQbCDHE ) and QaQb(D E ) One-electron transfer between the quinones involves 12 possible states, with 10 independent equilibrium constants and pKs [17] ... 

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