Studies of Alkyl Free Radicals and Reaction Mechanisms by Photoelectron Spectroscopy

Citation

Houle, Frances Anne (1979) Studies of Alkyl Free Radicals and Reaction Mechanisms by Photoelectron Spectroscopy. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/zppe-fp18. https://resolver.caltech.edu/CaltechTHESIS:11022009-081650291

Abstract

Application of vacuum ultraviolet photoelectron spectroscopy (UPS) to the study of simple alkyl free radicals and organic reaction mechanisms is described. A brief overview of the field of UPS of chemical transients, including a survey of the relevent literature, and a general introduction to topics covered in this thesis are given in Chapter 1. Chapters 2, 4 and 5 present results of UPS investigations of the first photoelectron bands of alkyl radicals produced by pyrolysis of the corresponding alkyl nitrites. Spectra have been obtained for methyl, ethyl, 1-propyl, 2-propyl, tert-butyl, cyclopentyl, cyclohexyl and 2-norbornyl radicals. Adiabatic ionization potentials determined for these species are used to calculate heats of formation of the ions, heterolytic bond dissociation energies of the corresponding alkanes, and proton affinities of the corresponding olefins. The shapes of the bands are discussed qualitatively in terms of structural differences between neutrals and positive ions. Chapter 3 is a discussion of the lowest energy conformations of ethyl and tert-butyl radicals. In particular, ESR and theoretical results from the literature are used to discuss the question of the planarity of alkyl radical centers. Chapters 4 and 6 present results of studies of the thermal decomposition mechanisms of 2-norbornyl, cyclopentyl and cyclohexyl radicals. Pyrolysis of the radicals is readily observed under the conditions necessary for their generation. The mechanisms deduced from the spectra are compared to those resulting from studies using classical techniques. In Chapter 7, experiments designed to assess the fate of reaction exothermicity in the pyrolysis of some strained azo compounds are described. The results indicate that very little of the available energy is released to vibration of the N_2 fragment. The implications of this observation for the transition states of the reactions that were studied are discussed.

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