Cathodic shift

In each series the oxidations show monotonic cathodic shifts, while the reductions show monotonic anodic shifts as the heteroatom increases in atomic number. Thus it is easier both to oxidize and reduce the heavier diheteroferrocenes. 

For the oxidations, the cathodic shifts (P— As- Sb- Bi) are nearly the same for the tetramethyl series and the octamethyl series. Since the shifts are independent of the degree of methyl substitution, these shifts can be used to estimate the 1/2 values for the series of unsubstituted diheteroferrocenes from the experimental value for l,l -diarsaferrocene. 

Mohamed [63] investigated the complexation behavior of amodiaquine and primaquine with Cu(II) by a polarographic method. The reduction process at dropping mercury electrode in aqueous medium is reversible and diffusion controlled, giving well-defined peaks. The cathodic shift in the peak potential (Ep) with increasing ligand concentrations and the trend of the plot of EVl versus log Cx indicate complex formation, probably more than one complex species. The composition and stability constants of the simple complexes formed were determined. The logarithmic stability constants are log Bi = 3.56 log B2 = 3.38, and log B3 = 3.32 [Cu(II)-primaquine at 25 °C]. 

Polarography of Ph3PbAc, 1.084 x 10 4 M in the same electrolyte solution gave, at pH 7.0, E /2 values of —0.425 and —1.075 V (SCE) which, too, show cathodic shifts with increasing pH. Unlike Bu2PbAc2, Ph3PbAc undergoes a SET reduction to radicals, which adsorb on the DME and react with mercury ... 

The reduction potentials were determined by polarography, and by CV on a hanging Hg cathode, and were irreversible, though the presence of a reverse wave was noted. Evidently, here the group 14 elements are directly affected (Table 14). The cathodic shift is understandable when L in Ph3MCo(CO)3L is changed from CO (an acceptor ligand) to the donors phosphine or phosphite. Anodic shift of the first reduction potential in the... 

Further evidence for the above-mentioned mechanism of HOMO elevation by group 14 elements is provided by studies of thioethers. The decrease in oxidation potential of silyl ethers as compared to ethers is not realized in the case of a-silylthioethers whereas a-stannyl substituents in thioethers cause a considerable cathodic shift in oxidation potential. Moreover, the effect is geometry-dependent. Values for substituted cyclic dithianes 15 are summarized in Table 21. The difference between Si and Sn in this case is illustrative. The lone nonbonding pair in the 3p orbital of sulfur is much too low in energy compared to... 

Ge like Sn shows the ft effect, namely promotion of electron energy levels in an oxygen atom once removed. The effect is apparent in ethers, i.e. alkoxygermanes as well as acylgermanes. Voltammetry by RDE shows considerable cathodic shifts in the oxidation... 

Upon addition of Ba2+ cations, the 2+/l+ bipyridinium redox couple is shifted anodically by 45 mV and the l+/0 couple is shifted cathodically by 10 mV. K+ and NH4 produce similar effects (Table 15). However, addition of Na+ cations causes a small cathodic shift to the 2+/l+ couple and an anodic perturbation to the l+/0 couple. This is in agreement with the proposed conformational change pathway for coupling the complexation and redox reactions. 

The cathodic shifts of the redox potentials of compounds [68], [69] and [71] on addition of halide anions are due to the stabilization of the cobaltocenium cation by the bound anion which causes the redox couple to shift to a more... 

Obtained in MeCN solution containing 0.2 mol dm-3 B114NBF4 as supporting electrolyte. Solutions were 2 x 10-3 mol dm 3 in ligand, and potentials were determined with reference to SCE. Three-electron reduction process as determined by coulometric experiments. Cathodic shift in reduction potential produced by the presence of anions (4 equiv) added as their ammonium of butylammonium salts. Values obtained in DMSO solution. 

The results of electrochemical investigations are summarized in Table 19. It is noteworthy that chloride, by virtue of its higher charge density, causes relatively larger cathodic perturbations than bromide. Interestingly, as observed with monosubstituted cobaltocenium derivatives, the dihydrogen phosphate anion produces the largest cathodic shifts. 

The addition of tetrabutylammonium adipate to electrochemical solutions of compound [86] led to a cathodic shift of 50 mV, suggesting that this receptor can electrochemically recognize this dianionic guest in acetone solution. Similar electrochemical experiments with other biscobaltocenium receptors gave inconclusive results because of solubility problems. 

The electrochemical properties were investigated by CV and SWV. The effects of adding anions to solutions of the porphyrin are summarized in Table 20. Interestingly, the porphyrin reduction waves are not significantly perturbed by any anionic guest, but the cobaltocenium moieties do show cathodic shifts of up to 225 mV with the dihydrogenphosphate anions. 

Obtained in acetonitrile solution containing 0.1 mol dm-3 BuJNPF6 as supporting electrolyte. Cathodic shifts of reduction potential produced by presence of anions (up to 10 equiv) added as their tetrabutylammonium salts. Precipitation of complex prevented a AE value from being determined. 

Refer to footnote a Table 23. h pa and pc represent the anodic and cathodic current peak potentials of the ferrocene/ferrocenium redox couple of the free ligand. Cathodic shifts in the ferrocene redox couples produced by the presence of anion (5 equiv) added as the tetrabutyl-ammonium salts. As the concentration of the anion increased, the ferrocene/ferrocenium redox couple began to exhibit the features of an EC mechanism. 

This is the region of the OCP. For an HF electrolyte without an oxidizing agent the electrode is inert, because no chemical reaction occurs at the front (emitter) at this potential range. The OCP depends on illumination condition, substrate doping density, illumination condition, HF concentration and DOC [Otl]. For moderately doped Si substrates in 5% aqueous HF the OCP is usually close to -0.6 V versus SCE in the dark. Under illumination a small negative (cathodic) shift to -0.64 versus SCE is observed for n-type electrodes, while the OCP for p-type substrate shifts significantly in positive (anodic) direction to -0.2 V versus SCE [Be9]. 

The reduction potential of9 (Figure 3.3) is almost identical to the potential of pristine CgQ, which may be due to the electron-withdrawing effect of the phenylethynyl group canceling out the above-mentioned expected cathodic shift [11]. 

Onset of anodic photocurrent at electrodes, coated by 673 PbS-containing Nafion showed a cathodic shift with increasing band-gap... 

Starting with catenane 174+, obtained by interlocking macrocycle 16 with only one cyclophane 124+, it is found, in agreement with these expectations, that the two bipyridinium units of 124+ undergo their first reduction in separated processes that are cathodically shifted with respect to the free cyclophane (Fig. 13.17a). Comparison... 

---