Absolute-Structure Determination: Past, Present and Future

Single-crystal X-ray crystallography is the major analytical technique in use today for absoluteconfiguration determination. The origins of absolute-structure determination, starting from Friedel's 1913 proof that the intensities of the opposites hkl and (h) over bar(k) over bar(l) over bar are identical, are traced. The important structural principles derived from the study of chiral, but pseudo-mirror symmetric, methyprylon are described. For the present time, the use of the average and difference intensities of the opposites hkl and (h) over bar(k) over bar(l) over bar are stressed. This leads to the use of Friedif, of 2AD and selected D plots, of R-merge and the D-Patterson. The best techniques for absolute-structure determination in the future are described. Some advice to the scientific community concludes the paper.