By means of variable temperature NMR spectra, conformation of 8-C-glucosyl prunetin, isolated from the leaves of Dalbergia hainanensis (Leguminosae), was studied. The restricted rotation around the C (sp3)-C (sp2) bond in the C-glucosides isoflavonoid results in two main conformers (syn and anti). With the help of MM calculation, the preferred conformation A has H-1 gauche to the 7-OCH3. The barrier to rotation was 18.1 kcal/mol. This result agrees with the calculated value 16.2 kcal/mol of free energy of activation for the interconversion between the conformers.
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