2887-41-4Relevant academic research and scientific papers
Entropy control of the cross-reaction between carbon-centered and nitroxide radicals
Sobek,Martschke,Fischer
, p. 2849 - 2857 (2007/10/03)
Absolute rate constants for the cross-coupling reaction of several carbon-centered radicals with various nitroxides and their temperature dependence have been determined in liquids by kinetic absorption spectroscopy. The rate constants range from 5 M-1 s-1 to 2.3 × 109 M-1 s-1 and depend strongly on the structure of the nitroxide and the carbon-centered radical. Grossly, they decrease with increasing rate constant of the cleavage of the corresponding alkoxyamine. In many cases, the temperature dependence shows a non-Arrhenius behavior. A model assuming a short-lived intermediate that is hindered to form the coupling product by an unfavorable activation entropy leads to a satisfactory analytic description. However, the behavior is more likely due to a barrierless single-step reaction with a low exothermicity where the free energy of activation is dominated by a large negative entropy term.
