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 Isotropic atomic chemical shifts σ in units of ppm were computed as differences between atomic isotropic shielding in solutes and corresponding reference atoms in tetramethylsilane (TMS) for each family. When more than a single conformer is considered, σ values are reported as an average value of conformers. Theoretical chemical shift data were evaluated relative to experiment based on linear correlation (R2) in order to assess the ability of the various approaches. The calculations were carried out with Gaussian 03 [7].