Kinetics and mechanisms of some free radical reactions

Abstract

This thesis consists of four parts. The main two parts provide more kinetic data on free radical addition reactions. This data is used to extend existing theories. The data obtained in the first part filled an important gap in kinetic data for radical addition reactions. These data of perfluoro-ethyl radical addition to ethylene and fluoro-ethylenes provided data for an increasing branching in the series CF₃., CF₃CF₂, (CF₃)₂CF. and (CF₃)₃C. Radicals and in addition for an increasing chain length in the series CF₃ ., CF₃CF₂. CF₃CF₂CF₂, and CF₃(CF₂)₂CF₂.radicals. The new data followed the sequence expected and established that the reson¬ ance stabilisation of the adduct radical in radical addition reactions to olefins is of minor importance. Instead there is a complex interplay of polar, steric and bond strength terms, all of which are necessarily inter-related in governing the rate and orientation of free radical addition reactions. The second part involved the addition of trifluoromethyl radicals to acetylene, alkyl and fluoroalkyl substituted acetylenes. The results showed similarity in the rates and orientation of addition to acetylenes and the corresponding sub¬ stituted ethylenes. This reveals that the substituents have very similar effects on the reactivity of the double and triple bonds. On the other hand, the Arrhenius parameters were significantly higher for the addition to acetylenes compared to the addition to ethylenes. This confirmed the transition theory predictions. The work also offers a study of the stereospecificity of the addition reaction with acetylenes. The third part involves the addition of trifluoromethyl radicals to 1,3-butadiene, isoprene, trans-piperylene and vinyl acetylene. The stereospecificity of the addition reaction with 1, 3-butadiene was studied. The fourth part deals with the topic "homosolvolysis", a study of the homolysis of carbon-halogen, carbon-metal, metal-metal and metal-halogen bonds using di-t-butylnitroxide and 2,2,5,5-tetramethylpyrrolydine nitroxide as solvents.