Fragmentation of a dioxolanyl radical via nonstatistical reaction dynamics: characterization of the vinyloxy radical by ns time-resolved laser flash photolysis

Bucher, G. , Lal, M., Rana, A. and Schmittel, M. (2018) Fragmentation of a dioxolanyl radical via nonstatistical reaction dynamics: characterization of the vinyloxy radical by ns time-resolved laser flash photolysis. Physical Chemistry Chemical Physics, 20(30), pp. 19819-19828. (doi: 10.1039/C8CP03311K) (PMID:30033465)

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Abstract

The photochemistry of two Barton esters, one derived from a dioxolane carboxylic acid and the other from pivalic acid, was investigated by product analysis and nanosecond laser flash photolysis (LFP). As expected, photolysis of the pivalate ester resulted in formation of the pyridine-2-thiyl and the t-butyl radical. Photolysis of the Barton ester of 2,2-dimethyl-1,3-dioxolane-4-carboxylic acid, on the other hand, revealed a complex multi-step fragmentation. In addition to the pyridine-2-thiyl and dioxolanyl radical, we gained evidence for the formation of the vinyloxy radical, CH2[double bond, length as m-dash]CHO˙. The latter was identified in the LFP by its π-complexes with benzene and diphenylether, its rapid quenching by electron-rich arenes and tri-n-butyl tin hydride, and its oxidative power in presence of trifluoroacetic acid as demonstrated by the oxidation of ferrocene to ferrocenium. Formation of CH2[double bond, length as m-dash]CHO˙ can be rationalized via fragmentation of the dioxolanyl radical. As the calculated barriers are too high for the reaction sequence to occur on the LFP time scale, we investigated the fragmentation of the photoexcited Barton ester via Born–Oppenheimer molecular dynamics simulations. In one trajectory, we could observe all reaction steps including ring opening of the dioxolanyl radical, suggesting that the excess energy gained in the ester cleavage and decarboxylation may lead to fragmentation of the hot dioxolanyl radical.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Bucher, Dr Goetz
Authors: Bucher, G., Lal, M., Rana, A., and Schmittel, M.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Physical Chemistry Chemical Physics
Publisher:Royal Society of Chemistry
ISSN:1463-9076
ISSN (Online):1463-9084
Published Online:18 July 2018
Copyright Holders:Copyright © 2018 the Owner Societies
First Published:First published in Physical Chemistry Chemical Physics 20(30): 19819-19828
Publisher Policy:Reproduced under a Creative Commons License

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