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Conformational analysis of 5,6,7-trisubstituted flavones: 13C NMR and molecular mechanics study

✍ Scribed by Rodolfo R. Biekofsky; Carlos A. Buschi; Alicia B. Pomilio

Publisher
John Wiley and Sons
Year
1991
Tongue
English
Weight
568 KB
Volume
29
Category
Article
ISSN
0749-1581

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✦ Synopsis

C NMR spectra of six flavones from Gomphrena martiana were analysed and compared with those of two related flavones isolated from Popowiu caulipora. This series of compounds has a similar substitution pattern on ring A, all compounds having oxygenated substituents on C-5, C-6 and C-7. Consistent trends in relating conformation to substituent chemical shift effects (SCS) were found by analysing the '3C NMR data for these compounds. ChemicaI shifts for ring A carbons were calculated using tbe principle of additivity of substituents and by taking into account the conformation of the substituents. A reasonable agreement between the calculated shifts and the experimental values was found. A molecular mechanics study of these compounds was undertaken in order to obtain a set of consistent molecular structures to search for correlations between molecular structure and measured 13C chemical shifts. Good agreement was found between the predicted molecular mechanics conformations and the "C NMR spectral data.

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