On the non-centrosymmetric structures which produce centrosymmetric diffraction patterns even with anomalous dispersion

The geometrical conditions that a structure gives centrosymmetric diffraction patterns have been investigated. It is shown that Friedel's law may hold for certain non-centrosymmetric structures containing two or more kinds of anomalous scatterer. Therefore, their absolute configurations can never be established by ordinary absorption-edge techniques. The geometrical characteristics of such a structure are discussed in terms of a vector set.