Deprotonation Of Cation Radical Research Articles

Mechanistic investigation of xanthene oxidation by heterogeneous and homogeneous electron transfers

Anodic oxidation of xanthene is investigated in acetonitrile at a platinum electrode by means of cyclic voltammetric and exhaustive potentiostatic electrolysis techniques. On the voltammetric scale time, the process involves two electrons and leads to xanthydrol. The corresponding mechanism is an ECE (electron–deprotonation–electron) type electrode reaction, the rate-determining step being the deprotonation of the cation radical obtained after the first electron transfer. On the other hand the analysis of the oxidation by homogeneous redox catalysis is carried out, using three organic catalysts. This allows the determination of the rate constants of the homogeneous electron transfers between xanthene and catalysts, the xanthene cation radical deprotonation rate constant and the standard potential of the xanthene cation radical/xanthene couple.

The Role of Homolytic Bond Dissociation Energy in the Deprotonation of Cation Radicals. Examples in the NADH Analogues Series

The deprotonation of the cation radical of 9-cyanomethylacridane by a series of normal bases is investigated and its pKa and homolytic bond dissociation energy determined experimentally. The latter...

On the deprotonation of the cation radicals of substituted ethylenes. A heterolytic or homolytic process?

Abstract The deprotonation of several cation radicals of substituted ethylenes in a monohydrated, monoammoniated or dihydrated cluster has been theoretically studied using an ab initio method through the 6-31G(D, P) basis set. It has been found that the cation radicals are π radicals, whereas the corresponding deprotonated species are σ radicals, the deprotonation process involving an intramolecular electron transfer from a σ to a π molecular orbitals. The experimental findings about the deprotonation reactions of organic cation radicals that have charge delocalized from the departing proton have been confirmed. The dissociation of the carbon-hydrogen bond begins with the homolytic stretching of the CH bond and then becomes a heterolytic dissociation, the transition state appearing very near the region of the crossing between both diabatic potential energy surfaces. The global proton transfer can therefore be described as a concerted transfer of a hydrogen atom and an electron in opposite senses.

Steric and Kinetic Isotope Effects in the Deprotonation of Cation Radicals of NADH Synthetic Analogs

Steric and Kinetic Isotope Effects in the Deprotonation of Cation Radicals of NADH Synthetic Analogs

On the mechanism of amine oxidations by P450.

1. Experimental data previously used to support an electron/proton transfer mechanism for oxidative dealkylation of amines by P450 are critically analysed with the conclusion that the mechanistic evidence is indecisive. 2. A new mechanistic criterion recently proposed to distinguish between electron/proton transfer and hydrogen atom transfer mechanisms is discussed. It is based on isotope effect profiles determined for the deprotonation of a series of para-substituted N-methyl-N-trideuteriomethyl)aniline cation radicals by pyridine and for hydrogen atom abstraction from the corresponding neutral amines by the tert-butoxyl radical. These reactions model the steps proposed in the two P450 mechanisms. 3. Isotope effect profiles measured for the demethylation of substituted NN-bis(dideuteriomethyl)anilines by four different forms of P450 were found to be experimentally indistinguishable from the hydrogen atom transfer profile, and distinctly different from the cation radical deprotonation profile. This provides strong evidence that P450 oxidatively dealkylates the amines by a hydrogen atom transfer mechanism and not by an electron/proton transfer mechanism.

Side-chain oxidation of .alpha.-substituted 4-methoxytoluenes by potassium 12-tungstocobalt(III)ate. The effect of .alpha.-substituents on the formation and deprotonation of the intermediate cation radicals

A kinetic study of the side-chain oxidation of α-substituted 4-methoxytoluenes (4-MeOPhCH 2 R, R=H, Me, OH, OMe, OAc, CN) by K 5 Co III W 12 O 40 .11H 2 O (Co(III)W) in AcOH/H 2 O (55:45) has been carried out. The reactions follow complex kinetics, suggesting that both the electron transfer and the radical cation deprotonation steps influence the reaction rate. A careful kinetic analysis has allowed the determination of the values of k 1 , the rate constant for the electron transfer step, and of k -1 /k 2 , the ratio between the rate constant of the back electron transfer and the one of the deprotonation of the cation radical

Photoinduced electron-transfer oxygenation of arylalkanes. Generation and oxygenation pathways of benzylic-type free radicals from the cation radical deprotonation

2,4,6-Triphenylpyrylium tetrafluoroborate(TPP +)-sensitized oxygenation has been carried out for several arylalkanes in dichloromethane. Direct evidence for deprotonation of a cation radical was obtained, and interesting structural effects on the deprotonation efficiency was observed.

Anodic oxidation of 1-naphthylamine in methylene chloride—temperature effects

The anodic oxidation of 1-naphthylamine (ArNH 2) has been studied at the platinum and vitreous carbon electrodes in methylene chloride (MC) by cyclic voltammetry and controlled-potential electrolysis. These studies confirm previous work in other solvents, but, because of the fact that MC allowed us to work up to −70°C, the temperature effects on product distribution could be analysed. Some aspects of the mechanism previously proposed have also been confirmed. The electrooxidation of ArNH 2 in MC gives only two dimeric products, ie 1,1'-naphthidine ( D 1) and 4-amino-1,1'-dinaphthylamine (D II whose yield are highly dependent on the temperature. Thus at temperatures higher than 20°C practically only D II is detected while at temperature of −60°C is D I predominant. Two competitive processes for the dimerization of the ArNH 2 + produced in the first charge transfer step are proposed. The inverse effect on temperature observed for the formation of D I is explained considering a previous equilibrium to dimerization, which involves a charge transfer complex between two ArNH 2 .+ species. On the other hand D II formation is proposed through dimerization of ArNH . following deprotonation of cation radical. A semiquantitative method to be applied to cyclic voltammograms and based on the kinetic expression is proposed to determine the selectivities of the competitive processes.

Photo-CIDNP study of adenosine 5'-monophosphate. Pair-substitution effects due to cation radical deprotonation

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhoto-CIDNP study of adenosine 5'-monophosphate. Pair-substitution effects due to cation radical deprotonationR. M. Scheek, S. Stob, T. Schleich, N. C. M. Alma, C. W. Hilbers, and R. KapteinCite this: J. Am. Chem. Soc. 1981, 103, 19, 5930–5932Publication Date (Print):September 1, 1981Publication History Published online1 May 2002Published inissue 1 September 1981https://doi.org/10.1021/ja00409a062RIGHTS & PERMISSIONSArticle Views77Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Étude par spectroélectrochimie de la cinétique de déprotonation d'un radical cation évaluation de son p KA

Spectroelectrochemistry by transmission is applied to the study of 1-( p-methoxyphenyl)-3,5-diphenyl-2-pyrazoline, using simple potential step with relaxation in acetonitrile in presence of pyridine derivatives. The kinetic results of the cation radical deprotonation are discussed in order to estimate a p K A value of this radical.