Electronic Redistributions

Fig. 1. The rate-determining step in the neutral hydrolysis of paramethoxy-phenyl dichloroacetate. In the reactant state (a) a water molecule is in proximity of the carbonyl carbon after concerted proton transfer to a second water molecule and electron redistribution, a tetrahedral intermediate (b) is formed.

Section 4.04.1.2.1). The spectroscopic and the diffraction results refer to molecules in different vibrational quantum states. In neither case are the- distances those of the hypothetical minimum of the potential function (the optimized geometry). Nevertheless, the experimental evidence appears to be strong enough to lead to the conclusion that the electron redistribution, which takes place upon transfer of a molecule from the gas phase to the crystalline phase, results in experimentally observable changes in bond lengths. 

The transfer of an element from the metal to the slag phase is one in which the species goes from the charge-neutralized metallic phase to an essentially ionic medium in the slag. It follows that there must be some electron redistribution accompanying the transfer in order that electro-neutrality is maintained. A metallic atom which is transfened must be accompanied by an oxygen atom which will absorb the elecuons released in the formation of tire metal ion, thus... 

The change in the electronic redistribution on transferring the molecule from the gas phase to aqueous solution is another interesting issue. Analysis of the computed Mulli-ken charge population demonstrates a substantial change on the hydrogen and oxygen in... 

These are essentially electron redistributions that can take place in unsaturated, and especially in conjugated, systems via their n orbitals. An example is the carbonyl group (p. 203), whose properties are not accounted for entirely satisfactorily by the classical formulation (21a), nor by the extreme dipole (21b) obtainable by shift of the n electrons ... 

The solvent reorganization term reflects the changes in solvent polarization during electron transfer. The polarization of the solvent molecule can be divided into two components (1) the electron redistribution of the solvent molecules and (2) the solvent nuclear reorientation. The latter corresponds to a slow and rate-determining step involving the dipole moments of the solvent molecules that... 

Bajorath, J., D. H. Kitson, G. Fitzgerald, J. Andzelm, J. Kraut, and A. T. Hagler. 1991. Local Density Functional Calculations on a Protein System Folate and Escherichia Coli dihydrofolate reductase. Electron Redistribution on Binding of a Substrate to an Enzyme. PROTEINS 9, 217. 

If one rotates about a C-C single bond in a compound of type X-C-C-Y, at each step of this torsional motion there are electron redistributions, and the bond lengths and angles will change. This phenomenon is the basis of the local nature of molecular structure. Several examples are illustrated in Figs. 7.6 and 7.7. 

The cyclo-oligomer products are formed in final reductive elimination steps commencing from the octadienediyl-Ni11 and dodecatrienediyl-Ni11 complexes for the C8- and Ci2-cyclo-oligomer production channels, respectively. Reductive elimination is accompanied with a formal electron redistribution between the nickel and the organyl moieties, which will be analyzed in Section 5.4. 

One source of the failure has to do with the fact that the electrostatic potential does not take the energy of electron redistribution (the polarization energy) into account. This is likely to be more significant for trimethylamine (most polarizable) than for dimethyl ether, than for methyl fluoride (least polarizable). The problem can be addressed by explicitly taking the polarization energy into account. 

The different surface atoms on the Si(lll)-7 x 7 surface have chemically distinct properties. Because of the electron redistribution, each rest atom and corner hole is negatively charged, while each of the adatoms has a partial positive charge [19,47]. Consequently, the rest atoms and corner hole can be considered nucleophilic, and the adatoms electrophilic. An adjacent rest atom-adatom pair hence forms a dipolar or diradical entity although the closest rest atom-adatom spacing on Si(lll)-7 x 7 (4.5 A) is much larger than the dimer distance on Si(100)-2 x 1 (2.4 A) [48], this pair may be expected to show some similarities in reactivity to the dimer on the... 

Second, formation of weak bonds between substrate and enzyme also results in desolvation of the substrate. Enzyme-substrate interactions replace most or all of the hydrogen bonds between the substrate and water. Third, binding energy involving weak interactions formed only in the reaction transition state helps to compensate thermodynamically for any distortion, primarily electron redistribution, that the substrate must undergo to react. 

Another fairly conservative reaction is the removal or attachment of a single electron from/to a molecule. As already discussed in Chapter 5, Koopmans theorem equates the energy of the HOMO with the negative of the IP. This approximation ignores the effect of electronic relaxation in the ionized product, i.e., the degree to which the remaining electrons redistribute themselves following the detachment of one from the HOMO. If we were to... 

Given this structural representation of the n-ir excited state, one has to determine the extent to which the photochemistry of carbonyl compounds is actually explicable as continuous electron redistribution processes of such a species. In actual fact, it is found (3-6) that n-ir photochemical reactions are amenable to mechanistic discussion in electron detail using this model of the excited state. 

If a potential electron acceptor is built into the anion itself, electron redistribution within the excited state may represent an pseudointramolecular electron transfer. For example, in the photodehalogenation of halosubstituted diphenyl-indenyl anions, eq. 84 (257),... 

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