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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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
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
|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|
|Official Date:||May 1970|
|Institution:||University of Warwick|
|Theses Department:||Department of Chemistry|
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