ENANTIOMORPHISM AND 3-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 psi-scan profiles for triplet phases close to +90 or -90 degrees, 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.