Spectroscopic Studies of Some Semiquinone Radical Ions


Previous ESR and UV spectroscopic studies of semiquinone cations are reviewed. Cations of 4,4'-bipheno-semiquinones prepared by chemical oxidation of the corresponding diols and reduction of the quinones in sulphuric acid, were studied using ESR and UV spectroscopy. Oxidation of biphenyl-4,4'-diol in sulphuric acid leads to either the 4,4'-biphenosemiquinone cation or it's 3,3'-disulphonated derivative, whereas, oxidation in aluminium chloride-nitromethane yields only the parent cation. Reduction of 4,4'-biphenoquinone in dideutero-sulphuric acid initially gives the 4,4'-biphenos emiquinone cation which subsequently undergoes a stepwise exchange of the protons in the 3,3',5 and 5' positions for deuterons. A variable temperature study of this process is reported and discussed. Similar patterns of behaviour are observed in the 1,4-dihydroxybenzene-1,4-benzogquinone system, The 3,3',5,5'—te tra-t—bu ty 1-4, 4'-biphenosemiquinone cation under certain conditions undergoes dealkylation to give secondary radicals. Anions of some alkylated 4,4'-biphenosemiquinones were prepared by the air oxidation of the diols in a variety of solvent mixtures and studied by ESR. The solvent dependance of the hyperfine coupling constants for the 3,3',5,5'-tetramethyl- derivative are reported and discussed in terms of an equilibrium between semi-quinone anions and hydrogen-bonded complexes of such anions with the hydroxylic solvent. The theory of Gendell, Freed and Fraenkel is shown to be quantitatively in agreement with the results. A correlation between the electron-donating power of the solvent and the equilibrium constant for the dissocation of the hydrogen-bonded complexes is also discussed. Molecular orbital calculations were performed for the 4,4'-biphenosemiquinone system and it's 3,3',5,5'- tetramethyl-derivative. Changes in the hyperfine coupling constants between the anion and the cation of 4,4'-biphenosemiquinone are consistent with these qualitative predictions. Several electron donor compounds were treated with 3,3',5,5'-tetrachloro- and 3,3',5,5'-tetrabromo—4,4'— biphenoquinones. Paramagnetic products were only detected in the case of phenothiazine.

Divisions: College of Engineering & Physical Sciences > School of Infrastructure and Sustainable Engineering > Chemical Engineering & Applied Chemistry
Additional Information: Copyright © A.G. Wheway, 1974. A.G. Wheway asserts their moral right to be identified as the author of this thesis. This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without appropriate permission or acknowledgement. If you have discovered material in Aston Publications Explorer which is unlawful e.g. breaches copyright, (either yours or that of a third party) or any other law, including but not limited to those relating to patent, trademark, confidentiality, data protection, obscenity, defamation, libel, then please read our Takedown Policy and contact the service immediately.
Institution: Aston University
Uncontrolled Keywords: Spectroscopic studies,semiquinone radical ions
Last Modified: 28 Jun 2024 07:08
Date Deposited: 11 Jan 2011 14:07
Completed Date: 1974-03
Authors: Wheway, Ashley G.

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