Studies in electron spin resonance.

This thesis presents the results of our inquiry into the formation, structure and reactivity of free radicals, The radicals were generated by ?-irradiation or chemical reaction and were detected and studied by electron spin resonance spectroscopy. Our chief interest has been in the mechanisms by which delocalization of electron spin within radicals can be envisaged, and in how these mechanisms are related to the geometry of the radicals. Accordingly our experimental results are interpreted in terms of such current chemical concepts as spin density, spin polarization, conjugation, hyperconjugation and electronegativity. Chapter 1 sets forth the aims and methods of the research, while Chapter 2 describes the basic link between theory and experiment, showing how a comparison between experimental and theoretical hyperfine coupling constants leads to an estimate of the spin density distribution and geometry of radicals. The next two chapters deal with some hydride radicals; Chapter 3 is an account of the electronic structure and trapping site of the hydroxyl radical in ice and salt hydrates, whereas Chapter 4 treats the problem of the geometry of the radical N2H4+ and AH3 radicals. Chapters 5 and 6 concern the effect on the electron spin distribution of replacing the hydrogen atoms of AH3 radicals with other atoms, such as oxygen or fluorine, or groups of atoms, such as methyl groups. Although there is substantial evidence from reaction kinetics that the unstable intermediates in some inorganic reactions are free radicals, there is little direct evidence of the kind that electron resonance spectroscopy can provide. Chapter 7 describes some attempts to remedy this deficiency. The review which concludes the thesis reflects a recent rise in interest in the study of gaseous radicals by their electron resonance. This review grew out of our own interest in the effect of the environment on the structure of radicals.