Empirically predicted 13C NMR chemical shifts for 8‐hydroxyflavone starting from 7,8,4′‐trihydroxyflavone and from 7,8‐dihydroxyflavone
Raymond Evans March, Darcy C. Burns, David A. Ellis
Abstract
Raymond Evans March, Darcy C. Burns, David A. Ellis
Abstract
8-Hydroxyflavone is not found in nature. While the (13)C chemical shifts of 8-hydroxyflavone have been reported previously, the observed (13)C chemical shifts were not assigned. A previously reported empirical predictive tool has been applied in reverse in order to deconvolute the (13)C chemical shifts for 8-hydroxyflavone from each of those of 7,8,4'-trihydroxyflavone and 7,8-dihydroxyflavone together with those of 7-hydroxyflavone, 4'-hydroxyflavone, and flavone. The two sets of calculated (13)C chemical shifts for 8-hydroxyflavone are in good agreement with each other in that the average absolute difference is 0.4 ppm. The previously reported but unassigned (13)C chemical shifts for 8-hydroxyflavone have been assigned by matching them with the averages of the two sets of calculated (13)C chemical shifts for 8-hydroxyflavone such that the minimum average absolute difference is 0.63 ppm. The assigned (13)C chemical shifts of 8-hydroxyflavone may be used, along with the (13)C chemical shifts of the remaining monohydroxyflavones, as part of a predictive tool to rapidly assess the (13)C NMR spectra of C8-hydroxylated flavonoids.
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8-Hydroxyflavone is not found in nature. While the (13)C chemical shifts of 8-hydroxyflavone have been reported previously, the observed (13)C chemical shifts were not assigned. A previously reported empirical predictive tool has been applied in reverse in order to deconvolute the (13)C chemical shifts for 8-hydroxyflavone from each of those of 7,8,4'-trihydroxyflavone and 7,8-dihydroxyflavone together with those of 7-hydroxyflavone, 4'-hydroxyflavone, and flavone. The two sets of calculated (13)C chemical shifts for 8-hydroxyflavone are in good agreement with each other in that the average absolute difference is 0.4 ppm. The previously reported but unassigned (13)C chemical shifts for 8-hydroxyflavone have been assigned by matching them with the averages of the two sets of calculated (13)C chemical shifts for 8-hydroxyflavone such that the minimum average absolute difference is 0.63 ppm. The assigned (13)C chemical shifts of 8-hydroxyflavone may be used, along with the (13)C chemical shifts of the remaining monohydroxyflavones, as part of a predictive tool to rapidly assess the (13)C NMR spectra of C8-hydroxylated flavonoids.
Key concepts: Chemical shift, Chemistry, Chemical composition, Carbon-13 NMR, Analytical Chemistry (journal), Stereochemistry, Physical chemistry, Organic chemistry