Attempted characterisation of phenanthrene-4,5-quinone and electrochemical synthesis of violanthrone-16,17-quinone. How does the stability of bay quinones correlate with structural and electronic parameters?

Symes, M. , Wilkinson, D., Cioncoloni, G. and Bucher, G. (2020) Attempted characterisation of phenanthrene-4,5-quinone and electrochemical synthesis of violanthrone-16,17-quinone. How does the stability of bay quinones correlate with structural and electronic parameters? RSC Advances, 10, pp. 38004-38012. (doi: 10.1039/D0RA06519F)

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Abstract

In bay quinones, two carbonyl moieties are forced into close proximity by their spatial arrangement, resulting in an interesting axially chiral and nonplanar structure. Two representatives of this little-explored class of compounds were investigated experimentally in this work. Electrochemical oxidation of 4,5-dihydroxyphenanthrene failed to provide evidence for the reversible formation of phenanthrene-4,5-quinone. Even at temperatures as low as T = 229 K, cyclic voltammograms did not show any evidence for reversibility, indicating that phenanthrene-4,5-quinone likely is a reactive intermediate even at low temperatures. Electrochemical oxidation of the larger homologue 16,17-dihydroxyviolanthrone, on the other hand, was reversible, and the quinone could be characterised by spectroelectrochemical means. The results of quantum chemical calculations confirm the experimental findings and indicate that a bay dicarbonyl moiety, also found in a number of angucycline antibiotics, does not necessarily have to confer extreme reactivity. However, in a series of phenanthrene quinones with an equal number (zero) of Clar sextets and a varying number of bay carbonyl groups (zero to two), there was a clear correlation between the triplet energy, taken as a measure of biradical character, and the number of bay carbonyl moieties, with the lowest triplet energy predicted for phenanthrene-4,5-quinone (two bay carbonyl moieties).

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Bucher, Dr Goetz and Cioncoloni, Giacomo and Wilkinson, Mr Dylan and Symes, Professor Mark
Authors: Symes, M., Wilkinson, D., Cioncoloni, G., and Bucher, G.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:RSC Advances
Publisher:Royal Society of Chemistry
ISSN:2046-2069
ISSN (Online):2046-2069
Published Online:15 October 2020
Copyright Holders:Copyright © The Royal Society of Chemistry 2020
First Published:First published in RSC Advances 10:38004-38012
Publisher Policy:Reproduced under a Creative Commons license

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
190559Upgrading the small scale equipment base for early career researchers in the engineering and physical sciencesMiles PadgettEngineering and Physical Sciences Research Council (EPSRC)EP/K031732/1P&S - Physics & Astronomy