Derivative cyclic voltammetry cation radical

It has also been shown that the electrode response of some processes can appear to fit theoretical working curves in which the reaction order in the intermediate differs from the true value (Parker, 1981b). For example, the deprotonation of hexamethylbenzene radical cation studied by derivative cyclic voltammetry gave data which fitted theoretical data for a simple first order decomposition of the intermediate. However, the observed first order rate constants were found to vary significantly with the substrate concentration indicating a higher order reaction. A method was proposed to treat... 

Julid investigated the behavior of terfuran 22 and bis(thienyl)furan 23 by cyclic voltammetry as well as the EPR spectra of the radical cations derived from these two compounds. Condensation of the diketone 20 with sulfuric acid furnished furan 22 in 18% yield, while reaction of diketone 21 with hydrochloric acid produced 23 in 84% yield.In a related report, Luo prepared oligomeric bis(thienyl)furans via similar methodology. ... 

An interesting study [52] of the protonation kinetics and equilibrium of radical cations and dications of three carotenoid derivatives involved cyclic voltammetry, rotating-disk electrolysis, and in situ controlled-potential electrochemical generation of the radical cations. Controlled-potential electrolysis in the EPR cavity was used to identify the electrode reactions in the cyclic volt-ammograms at which radical ions were generated. The concentrations of the radicals were determined from the EPR amplitudes, and the buildup and decay were used to estimate lifetimes of the species. To accomplish the correlation between the cyclic voltammetry and the formation of radical species, the relative current from cyclic voltammetry and the normalized EPR signal amplitude were plotted against potential. Electron transfer rates and the reaction mechanisms, EE or ECE, were determined from the electrochemical measurements. This study shows how nicely the various measurement techniques complement each other. 

Fleischmann et al s 34 report cyclic voltammetry data for the oxidation of a series of aromatic hydrocarbons in a molten salt electrolyte, AlCl3-NaCl-KCl at 150°. Electrooxidation in this medium occurs at unusually low oxidation potentials. Tris-(p-substituted phenyl)amines, with the exception of tri (p-nitrophenyl) amine, yield very stable radical cations by all electrochemical criteria 380>S42 Mono- and bis-p-substituted triphenylamines, however, dimerize with rate constants ranging from 101 to 10s M 1 sec 1 to benzidines 176 (Eq. (237)), which subsequently are oxidized to the radical cations 177, whose ESR-spectra are observed. Dimerization is fastest with the p-N02 andp-CN-derivative, in accordance with HMO calculations, which predict the highest spin sensity in the p-position of these compounds 542 ... 

A number of coal-derived liquids were examined by cyclic-voltammetry and other electrochemical techniques and found to show some activity. At anodic potentials films form on glassy carbon electrodes. It is suggested that this film formation is caused by oxidative coupling of radical cationic species with neutral ring structures through a mechanism similar to that which causes charring and coking in coal conversion processes. 

Two new alkylsulfanyl derivatives of pyrrole, 3,4-bis(methylsulfanyl)- and 3,4-bis(butylsulfanyl)-2,5-dimethyl-l-phenylpyrroles 843 have been prepared by different methods as good models to study the influence of the substituents into the generation and stability of their radical cations, by cyclic voltammetry and EPR spectroscopy. 2,5-Dimethyl-l-phenylpyrrole was reacted with A -bromosuccinimide to yield 3,4-dibromo derivative 842 in quantitative yield (Scheme 160) <2000J(P2)905>. 

These results, however, do not imply that mechanism C is impossible in general [228]. Recently, sterically hindered enol acetates, where nucleophilic attack (mech. A) and deprotonation (mech. B) on the radical cation stage are suppressed, were synthesized and studied by cyclic voltammetry as well as by product analysis [229]. Accordingly, enol acetates 146-149 undergo loss of CH3CO upon one-electron oxidation and open up a novel route to a-carbonyl cation chemistry. 150-153 rearrange subsequently to the benzofurans 19-21,23. The C-O bond cleavage reaction in 147 is rather slow (k < 10 s as derived from fast-scan cyclic voltammetry studies. 

Cyclic voltammetry on the cation 192 was not reversible attempted reoxidation of the reduction product of 192 produced the cation-radical of the tetraselenafulvalene 193. Apparently, the initially formed radicals dimerize rapidly with elimination of the SeEt groups at ambient temperatures. The cation-radical of 193 and various substituted derivatives have been reported,As with the sulfur analogs (see Section III,B,7,b), no comprehensive survey of the solid-state properties of these materials is attempted. In general, it is found that 193 and its derivatives, although rather more difficult to oxidize than tetrathiafulvalene counterparts, nevertheless do form electrically conducting salts and complexes. 

Methyl substituted benzonitriles were examined at a Pt anode in FSO3H/HOAC, at -76 °C, using cyclic voltammetry. At least two oxidation peaks were observed, the first corresponding to a 1-electron transfer leading to radical cations. This step was completely reversible for tetra- and pentamethyl derivatives and deprotonation only occurred at the second oxidation peak. However, with three or less methyl groups deprotonation was observed to occur at the first peak, generating a radical which was further oxidized to the corresponding cation that reacted with the solvent (Scheme 31). Cyclic voltammetry... 

A new class of highly conducting charge-transfer complexes (306 R=H or Me, X = Cl, Br, or I) has been prepared. ° Cyclic voltammetry of the bis(dithiafulvenyl)-derivatives (307) and (308) has been reported.Oxidation of the bis(dithiolan) (309) with iodine in the presence of aluminium chloride yields the crystalline radical cation salt (310). ... 

A full paper describes the studies of the Wisconsin group on the properties of derivatives of 9-azabicyclo[3.3.1]nonane. Photoelectron spectroscopy has been used to deduce the degree of flattening about the nitrogen atom and cyclic voltammetry to show the unusual stability of cation radicals in this series. Proton loss from the cation radical is disfavoured because of the constraints associated with Bredt s rule. 

Other a,co-disubstituted oligothiophenes such as 31 [24], 32 [103], 33 [104], 34 [105], 35 [106] and 36 [98] were characterized by cyclic voltammetry (Scheme 9.23). In 35, bulky bicyclo[2.2.2]octene substituents were introduced to prevent dimerization. Indeed, all oligomers derived from 35 (n = 0, 1, 2, 4) show stable radical cations and dications. In the case of the hexamer derived from 35 with n = 4, the two first one-electron reversible oxidation waves are nearly coalesced ( ox 0. 19, = 0.28 V vs FC/FC+)... 

Dian et al. [334] reported the electrochemical polymerization of 3-substituted and 3-,4-disubstituted selenophenes in acetonitrile saturated with lithium perchlorate. Two methods were used to study systematically the influence of the substituents on polymer formation cyclic voltammetry and chronoamperometry. The film formation process is greatly influenced by the electronic and steric effects of the substituents. For example, electron donating groups such as methyl and methoxy substituents appear to stabilize the radical cation intermediates, diminish the oxidation potential, and therefore allow polymer formation. The presence of halogen substituents raises the oxidation potential and does not lead to polymeric films. The conductivities of polyselenophene derivatives are quite low. For example, oxidized poly-3-methyl-selenophene and poly-3,4-dimethyl-selenophene have conductivities around 9 x 10 and 6 x 10" S cm", respectively. 

NDA reacts with primary amines in the presence of cyanide to produce 1-cyanobenz[f]isoindole (CBI) derivatives (Figure 5) [131]. Cyclic voltammetry reveals that the oxidation of the CBI involves the loss of an electron from the heterocyclic nitrogen forming a radical cation that further reacts and is therefore not available for reduction. In addition, the electrochemistry of NDA derivatives is virtually pH independent, indicating no gain or loss of a proton. 

Quantitative investigations of the kinetics of these a-coupling steps suffered because rate constants were beyond the timescale of normal voltammetric experiments until ultramicroelectrodes and improved electrochemical equipment made possible a new transient method calledjhst scan voltammetry [27]. With this technique, cyclic voltammetric experiments up to scan rates of 1 MV s are possible, and species with lifetimes in the nanosecond scale can be observed. Using this technique, P. Hapiot et al. [28] were the first to obtain data on the lifetimes of the electrogenerated pyrrole radical cation and substituted derivatives. The resulting rate constants for the dimerization of such monomers lie in the order of 10 s . The same... 

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