Dimerization cation effect

Fluorescence detected magnetic resonance effects observed during the pulse radiolysis of anthracene-d10 in the presence of tetramethylethene portray an additional facet of the cyclobutane radical cation system [345, 346]. The spectra [eight ( ) equivalent methyl groups, ad = 8.2 G approximately one half of the monomer splitting, am = 17.1 G] are compatible with a dimer cation. In analogy to the benzene dimer radical cation [347, 348] they were interpreted as evidence for a sandwich , one molecule above the other [346],... 

Mah et al. demonstrated the effect of counterions on the cationic polymerization of styrene [35-37]. The radiation-induced polymerization is much more sensitive to impurities than the catalytic polymerization, as the former involves the cationic species in a free ion state. Thus, one can expect, in the presence of stable anions, the promotion of the cationic polymerization because of the ion-pair formation between the dimer cation and the counterion. The effect was... 

The fast initiation step is followed by an equally fast propagation reaction. While the rate constant of the former has been measured by Kunitake and Takarabe the dimerisation kinetics have not been measured for this particular system. The following slow reactions consist of the proton transfer between the dimeric cation and the monomer to gjve alternatively the unsaturated dimer or the indanylic one. Finally, the protonated dimer can isomerise to a more stable configuration due to the direct interaction of the two phenyl groups through space polarisation effects Thus ... 

As the mobilities of ions mostly depend on E/N and N of ideal gas at constant temperature is proportional to P, varying P should not affect FAIMS analyses if E is scaled accordingly, i.e., when the results are presented as Eq/N versus Ex /N. That was found for systems investigated so far DMMP monomer and dimer cations (Figure 4.10) and methyl salicylate cation and anion, all in air. This situation is parallel to the trivial influence of gas T, where its only effect is varying A by the ideal gas law (3.5.3). In analogy to the dependence of Ec/N vs. Ex,/N) curves on T for... 

The negatively charged base reacts with the arylpalladium(II) halide to give the arylpalladium hydroxide or alkoxide complex, which is able to form the dimeric palladium-boron complex XXIII what is crucial for the transmetallation process [2-6]. It is apparent that the metal cation (from the base) accelerates the formation of the latter, as clearly showed by Zhang and coworkers [15]. They have developed the SM coupling procedure for sterically bulky arylboronic acids when the clear influence of the anion basicity and the cation effect were discovered. The cationic radius is presumably an important parameter which influences the formation of dimeric... 

The ion Co does not react with alkanes. However, CO addition to this ion leads to the formation of Co 2 CO which effectively attacks the C —H bond in alkanes. The rate constant of the reaction of activation of n-butane is at least two orders of magnitude higher for 00200 than for Co. In contrast to dimeric cations Co2 and FeCo", the trinuclear ion FeCo2 reacts with alkanes to give dehydrogenation products. The mononuclear ions generally split the C —C bond. 

Obviously, STFM is a facile and efficient approach to synthesize polymer, in particular PANI, nanostructures because it not only omits hard template and post-treatment of template removal but also simplifies reagents. However, the self-assembly mechanism of the conductive nanotubes of PANI by the STFM is not yet understood. It might be due to the formation of aniline dimer cation radicals which could act as effective surfactants to shape the polyaniline morphology. 

M. Chorro, C. Chorro, O. DoUadiUe, S. Partyka, R. Zana, Adsorption mechanism of conventional and dimeric cationic surfactants on silica surface effect of the state of the surface. J. Colloid Interface Sci. 210(1), 134-143 (1999). doi 10.1006/jcis.l998.5936 R. Chaghi, L.-C. de Menorval, C. Chamay, G. Derrien, J. Zajac, Interactions of phenol with cationic micelles of hexadecyltrimethylammonium bromide studied by titration calorimetry, conductiraetry, and IH NMR in the range of low additive and surfactant concentrations. J. Colloid Interface Sci. 326(1), 227-234 (2008). doi 10.1016/j.jcis.2008.07.035... 

The electron-transfer rate constant of the C q-PVCz system is larger than the system of Qo and Af-ethylcarbazole (EtCz) when Cgg is excited by the 532-nm laser, although EtCz corresponds to the unit structure of PVCz. The larger rate constant of PVCz can be attributed to the stable radical cation of PVCz due to the stacking of the carbazole moieties in the polymer chain as observed by the charge-resonance band in the near-IR region of the transient absorption spectra. The effect of the stacking of the carbazole moieties on the electron-transfer rate constants was discussed on the basis of the data on the electron-transfer processes between Cgg and various carbazole dimer models (Fig. 8) [57]. It has been confirmed that electron transfer proceeds effectively with the fuUy stacked carbazole dimers which stabilize the radical cations effectively. 

The dimerization of skatole proceeds in an entirely analogous manner, cation (44) now being the electrophilic reagent. This is sufficiently reactive to effect substitution at the a-position of a neutral skatole molecule. Attack by the less hindered side of cation (44) will be favored, leading to the stereochemistry shown in structure (30). The failure of 2-methylindole to dimerize is paralleled by the failure of 2-methylpyrrole dimer to react with a further molecule of 2-methylpyrrole. The main reason is almost certainly again the reduction in the electrophilic character of the immonium carbon by... 

The use of pyrrole and N-methylpyrrole was found to be preferable. Through the addition of N-methylpyrrole, all cationic side reactions could be effectively suppressed, and only dimerization products produced by Ni-catalysis were obtained. In this case the dimer selectivity was as high as 98 %. Scheme 5.2-21 shows the catalytic system that allowed the first successful application of [(H-COD)Ni(hfacac)] in the biphasic linear dimerization of 1-butene. 

Foreign cations can increasingly lower the yield in the order Fe, Co " < Ca " < Mn < Pb " [22]. This is possibly due to the formation of oxide layers at the anode [42], Alkali and alkaline earth metal ions, alkylammonium ions and also zinc or nickel cations do not effect the Kolbe reaction [40] and are therefore the counterions of choice in preparative applications. Methanol is the best suited solvent for Kolbe electrolysis [7, 43]. Its oxidation is extensively inhibited by the formation of the carboxylate layer. The following electrolytes with methanol as solvent have been used MeOH-sodium carboxylate [44], MeOH—MeONa [45, 46], MeOH—NaOH [47], MeOH—EtsN-pyridine [48]. The yield of the Kolbe dimer decreases in media that contain more than 4% water. 

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