Stereoelectronic interaction Ip(O1) -> sigma* (N1-O2) in a O-N-O unit was analyzed by means of R. Bader's Atoms in Molecule theory on the basis of X-ray diffraction data for dimethyl-(2R,4aR,5S,7R)-2,5,7-triphenylhexahydro-4H-[1,2]oxazino[2,3-b][1,2]oxazine-4,4-dicarboxylate. Atomic energies obtained by applying this approach to both the experimental and theoretical electron densities were used to probe the energy of this strong stereoelectronic interaction, giving consistent results with the NBO analysis, although showing its destabilizing character.