13C NMR Spectra of Lichen Xanthones. Temperature Dependent Collapse of Long-range Couplings to Hydrogen-bonded Hydroxyl Protons.
- 1 January 1978
- journal article
- research article
- Published by Danish Chemical Society in Acta Chemica Scandinavica
- Vol. 32b (3) , 177-181
- https://doi.org/10.3891/acta.chem.scand.32b-0177
Abstract
13C.sbd.1H Spin-spin coupling to the C-1 hydroxyl proton facilitated analysis of the single-resonance 13C NMR spectrum of norlichexanthone 1, the parent compound of all lichen xanthones. The substituent effects of chlorination and 0-methylation of 1 were studied and permitted interpretation of the spectra of 7 lichen xanthones. A temperature dependent collapse of the long-range couplings to the C-1 hydroxyl proton was found in the spectra of xanthones with chloro substituents and is ascribed to an increase in the rate of exchange of the C-1 hydroxyl proton catalyzed by the acidic protons in positions 3 and 6.Keywords
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