scholarly journals Electron and hydrogen self-exchange of free radicals of sterically hindered tertiary aliphatic amines investigated by photo-CIDNP

2013 ◽  
Vol 9 ◽  
pp. 437-446 ◽  
Author(s):  
Martin Goez ◽  
Isabell Frisch ◽  
Ingo Sartorius
Keyword(s):  
Ion Pairs ◽  
Activation Parameters ◽  
Radical Cations ◽  
Outer Sphere ◽  
Exchange Reactions ◽  
Radical Pairs ◽  
Time Resolved ◽  
Alkyl Radicals ◽  
Acid Base Equilibrium ◽  
Reorganization Energies

The photoreactions of diazabicyclo[2,2,2]octane (DABCO) and triisopropylamine (TIPA) with the sensitizers anthraquinone (AQ) and xanthone (XA) or benzophenone (BP) were investigated by time-resolved photo-CIDNP (photochemically induced dynamic nuclear polarization) experiments. By varying the radical-pair concentration, it was ensured that these measurements respond only to self-exchange reactions of the free amine-derived radicals (radical cations DH • + or α-amino alkyl radicals D • ) with the parent amine DH; the acid–base equilibrium between DH • + and D • also plays no role. Although the sensitizer does not at all participate in the observed processes, it has a pronounced influence on the CIDNP kinetics because the reaction occurs through successive radical pairs. With AQ, the polarizations stem from the initially formed radical-ion pairs, and escaping DH • + then undergoes electron self-exchange with DH. In the reaction sensitized with XA (or BP), the polarizations arise in a secondary pair of neutral radicals that is rapidly produced by in-cage proton transfer, and the CIDNP kinetics are due to hydrogen self-exchange between escaping D • and DH. For TIPA, the activation parameters of both self-exchange reactions were determined. Outer-sphere reorganization energies obtained with the Marcus theory gave very good agreement between experimental and calculated values of ∆G ‡ 298.

scholarly journals Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene

2013 ◽  
Vol 9 ◽  
pp. 1448-1454
Author(s):  
Martin Goez ◽  
Martin Vogtherr
Keyword(s):  
Electron Transfer ◽  
Photoinduced Electron Transfer ◽  
Nuclear Polarization ◽  
Activation Barrier ◽  
Activation Parameters ◽  
Radical Cations ◽  
Free Energies ◽  
Time Resolved ◽  
Diethyl Sulfide ◽  
Chemically Induced

Electron transfer between the title compounds and their radical cations, which were generated by photoinduced electron transfer from the sulfides to excited 2,4,6-triphenylpyrylium cations, was investigated by time-resolved measurements of chemically induced dynamic nuclear polarization (CIDNP) in acetonitrile. The strongly negative activation entropies provide evidence for an associative–dissociative electron exchange involving dimeric radical cations. Despite this mechanistic complication, the free energies of activation were found to be well reproduced by the Marcus theory of electron transfer, with the activation barrier still dominated by solvent reorganization.

Kinetics and mechanism of substitution reactions of (dimethylsulfoxide)pentaamminecobalt(III) ion in dimethylsulfoxide solvent: complications due to redox and conjugate base processes

1976 ◽  
Vol 54 (23) ◽  
pp. 3685-3692 ◽  
Author(s):  
S. T. Danny Lo ◽  
Evelyn M. Oudeman ◽  
Jean C. Hansen ◽  
Thomas W. Swaddle
Keyword(s):  
Ion Pairs ◽  
Activation Parameters ◽  
Rate Coefficients ◽  
Solvent Exchange ◽  
Exchange Reactions ◽  
Substitution Reactions ◽  
Enthalpy Of Activation ◽  
A Minor ◽  
Conjugate Base ◽  
Anation Rate

Simple anation and solvent exchange reactions of Co(NH3)5DMSO3+ in DMSO are accompanied by reactions in which the conjugate base of this complex undergoes either internal redox to cobalt(II) or relatively rapid substitution. These conjugate base reactions are eliminated by addition of H+, although a minor redox pathway persists within ion pairs of Co(NH3)5DMSO3+ with chloride or bromide. The latter pathway is evidently not mechanistically related to the solvent exchange or anation reactions, which proceed by dissociative interchange (Id) according to the activation parameters (volume of activation = +10 cm3 mol−1 for DMSO exchange; enthalpy of activation = 123, 121, and ∼126 kJ mol−1 for DMSO exchange and bromide and chloride anation respectively). Enthalpies of activation for solvent exchange and for the limiting anation rate are shown to be better criteria of mechanism than the corresponding rate coefficients.

Kinetics and mechanism of redox reactions of U(III) ions with monochloroacetic and dichloroacetic acids

1979 ◽  
Vol 44 (2) ◽  
pp. 401-405 ◽  
Author(s):  
Ľubica Adamčíková ◽  
Ľudovít Treindl
Keyword(s):  
Redox Reactions ◽  
Reaction Rate ◽  
Activation Parameters ◽  
Outer Sphere ◽  
Alcohol Concentration ◽  
Kinetics And Mechanism ◽  
Solvent Structure ◽  
Influence Of Ph ◽  
Sphere Mechanism

The kinetics and mechanism of the redox reactions of U3+ ions with mono- and dichloroacetic acids were studied. The influence of pH was observed mainly in the second case and led to the determination of the rate constants and activation parameters corresponding to two parallel steps, namely oxidation of U3+ with CHCl2COO- ions and oxidation of U3+ with CHCl2.COOH molecules. The influence of binary mixtures of water with methanol, ethanol, isopropanol, or tert-butenol on the reaction rate was followed. Increasing alcohol concentration influences the rate constant not only through changing dielectric constant and solvation of the reactants but also through a change of the solvent structure which plays a role in reactions with an outer sphere mechanism of the electron transfer.

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