I was lucky enough to attend the announcement made in 2012 of the discovery of the Higgs Boson. It consisted of a hour-long talk mostly about statistics, and how the particle physics community can only claim a discovery when their data has achieved a 5σ confidence level. This represents a 1 in 3.5 million probability of the result occurring by chance. I started thinking: how much chemistry is asserted at that level of confidence?
AbstractEssential background on the determination of absolute configuration by way of single‐crystal X‐ray diffraction (XRD) is presented. The use and limitations of an internal chiral reference are described. The physical model underlying the Flack parameter is explained. Absolute structure and absolute configuration are defined and their similarities and differences are highlighted. The necessary conditions on the Flack parameter for satisfactory absolute‐structure determination are detailed. The symmetry and purity conditions for absolute‐configuration determination are discussed. The physical basis of resonant scattering is briefly presented and the insights obtained from a complete derivation of a Bijvoet intensity ratio by way of the mean‐square Friedel difference are exposed. The requirements on least‐squares refinement are emphasized. The topics of right‐handed axes, XRD intensity measurement, software, crystal‐structure evaluation, errors in crystal structures, and compatibility of data in their relation to absolute‐configuration determination are described. Characterization of the compounds and crystals by the physicochemical measurement of optical rotation, CD spectra, and enantioselective chromatography are presented. Some simple and some complex examples of absolute‐configuration determination using combined XRD and CD measurements, using XRD and enantioselective chromatography, and in multiply‐twinned crystals clarify the technique. The review concludes with comments on absolute‐configuration determination from light‐atom structures. Chirality, 2008. © 2007 Wiley‐Liss, Inc.