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Reference: Simpson, Nigel J. K., (1990). Studies of transient free radicals in solution by flash photolysis E.S.R. DPhil. University of Oxford.Citable link to this page:

 

Studies of transient free radicals in solution by flash photolysis E.S.R

Abstract: An introduction is presented to the nature of polarized and non-polarized transientspin resonance signals, produced by flash-photolysis e.s.r., followed by a description ofthe equipment used for experimental work. Theories of Chemically Induced DynamicElectron Spin Polarization are reviewed and various models introduced to illustratethese concepts.A description is given of the first thorough investigation into the effect of CIDEPpolarization transfer down a free radical chain and expands upon the consequences ofhyperfine-dependent relaxation and the relative signs of coupling constants in variousradical species. It concludes with an account of two methods of kinetic analysis whichare the first practical demonstrations of their kind, and employ extension of expressionsdeveloped in earlier chapters.Studies are made of the CIDEP behaviour of radicals in high viscosity paraffins. Areassessment of previous published work is made: anomalous polarization behaviour wasfound to have been over-compensated for. A new method of extracting values for T1and T2,/sub> is demonstrated for strong transient e.s.r. signals.A collection of experimental data relating to the previously unexplained absorptivepolarization observed in the spectrum of ketyl radicals and the longer-time phaseinversion of hyperfine-dependent CIDEP is given. The operation of Triplet MechanismCIDEP in the ketyl radical systems is ruled out and a division of radicals intogeminately formed and free-encounter pairs is shown to be incapable of explaining theobserved phase changes. In its place a cross-relaxational mechanism, drawing uponsimultaneously generated nuclear spin polarization is advanced. Conclusions are drawnthat this may account for both anomalies.Lastly a photochemical application of CIDEP is demonstrated; two differentreaction intermediates are identified upon photolysis of ortho phthalaldehyde,depending upon the quenching conditions. A reaction scheme consistent with allexperimental data is proposed. A brief comment upon the photo-chemistry ofindan 2-one concludes this work.

Type of Award:DPhil Level of Award:Doctoral Awarding Institution: University of Oxford Notes:The digital copy of this thesis has been made available thanks to the generosity of Dr Leonard Polonsky

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McLaughlan, KeithMore by this contributor

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Keith McLaughlanMore by this contributor

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 Bibliographic Details

Issue Date: 1990Identifiers

Urn: uuid:dd9a8aa9-f68a-4362-af7e-6c052fa3a5fe

Source identifier: 603853228 Item Description

Type: Thesis;

Language: eng Subjects: Flash photolysis Free radicals (Chemistry) Tiny URL: td:603853228

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Author: Simpson, Nigel J. K. - institutionUniversity of Oxford facultyMathematical and Physical Sciences Division - - - - Contributors Mc

Source: https://ora.ox.ac.uk/objects/uuid:dd9a8aa9-f68a-4362-af7e-6c052fa3a5fe



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