Absolute-Structure Determination: Past, Present and Future.

Single-crystal X-ray crystallography is the major analytical technique in use today for absolute-configuration determination. The origins of absolute-structure determination, starting from Friedel's 1913 proof that the intensities of the opposites hkl and hkl 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 hkl are stressed. This leads to the use of Friedif, of 2 AD and selected D plots, of Rmerge 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.