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Issue 62, 2020
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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?

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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).

Graphical abstract: 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?

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Supplementary files

Article information


Submitted
27 Jul 2020
Accepted
24 Sep 2020
First published
15 Oct 2020

This article is Open Access

RSC Adv., 2020,10, 38004-38012
Article type
Paper

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?

D. Wilkinson, G. Cioncoloni, M. D. Symes and G. Bucher, RSC Adv., 2020, 10, 38004
DOI: 10.1039/D0RA06519F

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