Enantiomorphism and three-beam X-ray diffraction: determination of the absolute structure

It is shown that three-beam X-ray diffraction provides a means of resolving the enantiomorphism problem. It is based on the fact that three-beam interference leads to significantly different ψ-scan profiles for triplet phases close to +90 or −90°, which are selectors between enantiomorphs. Since this method works without the need of anomalous scattering, it is particularly suitable for resolving the absolute structure of light-atom compounds. The application of this method is discussed in detail. Its capability of distinguishing between enantiomorphs has been rejected in a recent paper by Colella [Acta Cryst. (1994), A50, 55–57]. Detailed comments on the invalid arguments of Colella's analysis are presented.