Atom transfer kinetics

A general treatment has been published of oxygen atom transfer kinetics for complexes wherein the dimerization/comproportionation reaction is a complicating feature.165 This treatment critically summarizes all pertinent earlier information. The assumption that dimerization is very fast with respect to oxygen atom transfer is born out by the agreement of the observed and calculated kinetic parameters. 

Internal Conversion. As an alternative to the emission of a y-ray, the available energy of the excited nuclear state can be transferred to an atomic electron and this electron can then be ejected from the atom. The kinetic energy of this electron is where E is the energy by which the... 

Lindemann <8> has made an interesting application of the new theory in the determination of the frequency of atomic vibration, r, from the melting-point. He assumes that at the melting-point, T the atoms perform vibrations of such amplitude that they mutually collide, and then transfer kinetic energy like the molecules of a gas. The mean kinetic energy of the atom will then increase by RT when the liquid is unpolymerised and the fusion occurs at constant volume this is the molecular heat of fusion. 

Nickel(IV) complexes react with dimethyl sulphoxide in acidic solution to give the sulphone and nickel(II) ions. The kinetics of this reaction have been studied and found to be very complex in nature. The reaction probably proceeds by initial complexation of the dimethyl sulphoxide to the nickel(IV) species followed by electron transfer and oxygen atom transfer producing the observed products149. 

That is, if one compares the cross-sections at the same kinetic energy E of the incident ion, the transfer of a H atom always occurs with a larger cross-section than the transfer of a D atom. (The cross-sections at the same relative kinetic energy are equal since the effective radial potential in which the particles move during the collision is the same for H- and D-atom transfer. The effective potential is the sum of the potentials... 

Based on C-H versus C-D zero point vibrational differences, the authors estimated maximum classical kinetic isotope effects of 17, 53, and 260 for h/ d at -30, -100, and -150°C, respectively. In contrast, ratios of 80,1400, and 13,000 were measured experimentally at those temperatures. Based on the temperature dependence of the atom transfers, the difference in activation energies for H- versus D-abstraction was found to be significantly greater than the theoretical difference of 1.3kcal/mol. These results clearly reflected the smaller tunneling probability of the heavier deuterium atom. 

Rehm D, Weller A (1970) Kinetics of fluorescence quenching by electron and H-atom transfer. Isr J Chem 8 259... 

Barbara PF, Walsh PK, Brus LE (1989) Picosecond kinetic and vibrationally resolved spectroscopic studies of intramolecular excited-state hydrogen atom transfer. J Phys Chem 93 29-34... 

A number of mechanistic pathways have been identified for the oxidation, such as O-atom transfer to sulfides, electrophilic attack on phenols, hydride transfer from alcohols, and proton-coupled electron transfer from hydroquinone. Some kinetic studies indicate that the rate-determining step involves preassociation of the substrate with the catalyst.507,508 The electrocatalytic properties of polypyridyl oxo-ruthenium complexes have been also applied with success to DNA cleavage509,5 and sugar oxidation.511... 

The distance xx describes the distance along the x-coordinate over which G increases by RT. We assume that motion along the x-coordinate is diffusive. This will be true for encounters, rearrangement of the ionic atmosphere or the rotation of solvent molecules. We further assume that at some distance xj the atom-transfer reaction becomes possible with a rate constant k. The diffusive kinetic equation then becomes (18), where the step function S(xt) = 0... 

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