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[摘要]：Density functional theory/B3LYP has been employed to optimize the coil formations of selected 4-arylflavan-3-ols and their phenolic methyl ether 3-O-acetatcs. The electronic circular dichroism spectra of the major conformers have been calculated using time-dependent density functional theory to Validate the empirical aromatic quadrant rule applied to the assignment of the absolute configuration of this class of compounds. The modest 6-31G* basis set was sufficient to produce reasonable spectra. The calculated Cotton effects at 220-240 nm, crucial for the assignment of the CA absolute configuration. result from electronic transitions of the molecular orbitals involving the pi-electrons of the spatially Close aromatic A-ring and 4-aryl moieties. The sign of this Cotton effect is determined by the orientation of the 4-aryl substituent: the negative and positive Cotton effects are associated with 4 alpha- and 4 beta-aryl substituents, respectively. |
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