A study of free radicals in liquid ammonia by electron spin resonance
Buick, Anthony Robert (1970) A study of free radicals in liquid ammonia by electron spin resonance. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b1732937~S1
A rapid flow method for the production of radical-anions for electron spin resonance (e.s.r.) observation is described whereby liquid ammonia solutions of sodium and substrate are mixed in the cavity of the spectrometer. The mixing-cell consists of several capillary tubes placed in a glass jacket narrowing at one end to form a nozzle. Liquid ammonia soltelons are passed under pressure of nitrogen through capillary tubes and interstices and radical-anlons can be observed within a few milliseconds of mixing. Results are presented in five chapters. The reduction of pyridine and substituted pyridines is described in ChapterII; with the exception of one mono- and all dicarboxylic acid derivatives, simple monomer radical-anions are formed. Pyridinecarboxylic acids ionise in liquid ammonia solution and in some cases the ionized proton attaches itself to the radical-anion forming an N- protonated species. N- protonation is also seen for pyridine itself when reduced in the presence of a large excess of ethanol, a strong acid in ammonia. A complementary static reduction technique is used to observe reduction on a longer time scale where several dimeric products are observed, for example 2,6-dimethylpyridine gives 2,2',6,6'-tetramethyl-4,4'-dipyridyl radical-anion. Carbon halogen bond-cleavage occurs rapidly when aryl hallides, except fluorides, are reduced (Chapter III). The halogen atom in fluorobenzonitriles shows varying degrees of lability; for example, a mixed spectrum of halogenated and dehalogenated radical-anions is seen for para-fluorobenzonitrile while even after the insertion of a one second delay between points of mixing and observation only the halogenated radical-anion is observed for meta-fluorobenzonitrile. Aromatic carboxylic acid reduction (Chapter IV) produces the expected radical-anions, with the exception of two nitro di-acids which produce a mixture of radicals on the flow system, and a spectrum possibly corresponding to a radical-anion similar to the parent nitro di-acid on static reduction. Analysis of the major flow spectrum again indicates a protonated species. Styrenes and benzamides show non-equivalent ring protons resulting in complex spectra (Chapters V and VI). The 'alpha effect' is used in Hückel and McLachlan molecular orbital calculatlons for styrenes where one ortho ring position is given a small Coulomb integral value. The results of the reduction of some -unsaturated ketones are discussed in Chapter VI. Analysis of the spectrum of mesityl oxide radical-anion is straightforward, while slow 'ring-flip' from one conformer to another is responsible for inequivalent methylene protons in isophorone and 2-cyclohexen-1-one.
|Item Type:||Thesis or Dissertation (PhD)|
|Subjects:||Q Science > QD Chemistry|
|Library of Congress Subject Headings (LCSH):||Electron paramagnetic resonance spectroscopy, Free radicals (Chemistry) -- Analysis, Liquid ammonia -- Analysis, Anions|
|Institution:||University of Warwick|
|Theses Department:||Department of Chemistry|
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