Abstract: 2D NMR (¹H-¹H COSY, ¹³C-¹H COSY, COLOC) and X-ray diffraction were used to study the structure of Pd-Ia. The proton signals in ¹H NMR and carbon signals in ¹³C NMR were assigned definitely. The mistake about the assignment of signals of geminal methyls in ¹³C NMR was corrected. Accordingly, some points concerning the determination of C-3' and C-4' relative configuration of the kind of the compounds decided by the value of chemical shifts difference of geminal methyls in ¹³C NMR were revised. It was discovered that the △δ of geminal methyls ≥ 2ppm for cis-configuration and the △δ of geminal methyls ≤ 2ppm for trans-configuration in ¹³C NMR, and △(δC-3' trans-δC-3'cis)>lppm.

Key words: 2D NMR, X-ray diffraction, Pd-Ia, Acylated khellactones, Relative configuration