Kinetics for Free-Radical Conversion Processes in Irradiated d,l-Valine

Publisher Website
Google Scholar
Abstract
The kinetics for two free‐radical conversions in irradiatedd,l‐valine has been studied by use of electron spin resonance(ESR)spectroscopy. In d,l‐valine three different radicals are observed. At 77°K only one of these radicals R(1) is formed, which upon subsequent warming converts into the intermediate radical R(2) with an efficiency of approximately unity. The reaction, studied in the temperature range 110–125°K, was found to be first order with an activation energy of 7.6 ± 0.2 kcal/mole. Upon further warming, a third radical R(3) is formed. This formation consists of two separate processes, each proceeding by first‐order kinetics. The activation energies,measured in the temperature range 200–260°K, are 6.6 ± 0.3 kcal/mole and 8.3 ± 0.5 kcal/mole, with the smaller activation energy process occurring at slightly lower temperatures. It was found that the concentration of R(3) , as observed after warming to 300°K, was significantly greater than the initial concentration of R(1) . This increase in total radical concentration is associated with the production of R(3) by the process having an activation energy of 6.6 kcal/mole. Possible mechanisms for the conversions are discussed in light of the known structures of R(2) and R(3) .