Oxidation-reduction reactions Electron configuration

Oxidation-reduction reactions can lead to efficient substitution processes, primarily because of the dramatic effect changing electronic configuration can have on substitution rates. The substitution of the inert NHj instead of relatively labile Cl" in [Cr(NH3)5Cl] in the presence of Cr is the classic example ... 

The removal of two X-type ligands leads to a decrease of two units in the metal s oxidation state the electronic configuration changes from d to 4" . The metal is therefore reduced, which explains the name reductive eliniination . The opposite reaction is called oxidative addition . 

Eclipsed conformation, 7, 254 Electrocyclic reactions, 341, 344-348 Electrol ic oxidation, 307 Electrolytic reduction, 307 Electromeric effect, 24 Electron configuration, 3 Electron density, 21, 26, 29, 393 Electron-donating groups, 23, 26 addition to 0=C and, 183 addition to 0=0 and, 205, 206 aromatic substitution and, 153, 158 pinacol change and, 115 Electronegativity, 21, 22, 95 Electrons, lone pair, 10, 72 Electron spin, paired, 2, 308 Electron-withdrawing groups, 23 acidity and, 59, 61, 62, 272... 

The dye radical formed by reduction of the dye molecule would have an additional electron, would not have the same electronic configuration, and possibly not the same geometric configuration compared to the excited dye molecule. Moreover, the electrochemical measurements contain contributions from solvation energy differences between the parent dye and its reduced or oxidized radicals (43). These contributions do not appear in the dye s optical transition energy. In addition, many cyanine dyes undergo irreversible redox reactions in solution and the potentials, as commonly measured, are not strictly reversible. Nevertheless, Loutfy and Sharp (260) showed that the absorption maxima of more than 50 sensitizing dyes in solution conformed approximately to the equation... 

Oxidation of Mercaptans by Ov. Mercaptans are autoxidized in the presence of 02 in alkaline medium. In general, the oxidation is slow in the absence of catalyst because of unfavorable spin state symmetries that result from differences in the electronic configuration of the reactants (54). However, the reaction proceeds rapidly in the presence of traces of metal ions or transition metal phthalocyanines (55—58). The catalyst tends to alter the electronic structure of either the reductant and/or 02 so as to surmount the activation energy barrier imposed on the reaction by spin-state symmetry restriction. The coupled oxidation system in the presence of catalyst can be represented by ... 

Each reaction type (oxidative addition, reductive elimination, etc.) was studied according to the electronic configuration (at this time only the even dn configurations have been considered), the coordination number, and the coordination geometry. The matrices that we have composed for the evaluation (Matrices 1, 2, 3, 4, 5, 6, and 7 see also Section I,C), show the structure d"-ML for which the reaction is allowed or forbidden. We must note that, in most of the cases, the rules that we present derivefrom theoretical studies found in the literature and that exceptions certainly exist. Another difficulty in this reaction evaluation is the importance of the coordination geometry (15b), related to the spin state (low or high), the choice of which is particularly difficult. 

One-electron oxidation of phenyl iron(III) tetraarylpor-phyrin complexes with bromine in chloroform at —60°C produces deep red solutions whose H and H NMR spectra indicate that they are the corresponding iron(IV) complexes. For the low-spin aryl Fe porphyrins the electron configuration is (dxyf(dxz,dyzf, with one tt-symmetry unpaired electron, and for the low-spin aryl Fe porphyrins the electron configuration is d, yf- d, zAyzf with two TT-symmetry unpaired electrons. The aryl Fe porphyrins are thermally unstable, and upon warming convert cleanly to A-phenylporphyrin complexes of Fe by reductive elimination. This process has been investigated by electrochemical techniques, by which it was shown that the reversible (at fast scan rates) one-electron oxidation of a-aryl complexes of PFe was followed by an irreversible chemical reaction that yielded the Fe complex of the A-phenylporphyrin, which could then be oxidized reversibly by one electron to yield the Fe complex of the A-phenylporphyrin. (If the Fe complex of the N-phenylporphyrin is instead reduced by one electron, the Fe complex of the A-phenylporphyrin is formed reversibly at... 

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