A set of conformers of α-mangostin, γ-mangostin and garcinone D (Figure 2) in gas phase were fully optimized at the Hartree-Fock level with a heteroatom-polarized valence-double-zeta basis set (HF/MIDI!). The ten most stable conformers for each molecule are selected for further study. We examined using three hybrid generalized-gradient approximation density functional, WP04, WC04, and B3LYP for predicting 1H and 13C chemical shifts.