Of the 65M known compounds, it is estimated only around 1M have been reported as scalemic, a term used to describe any non-racemic chiral compound. Of these, an unknown proportion have a clearly established absolute configuration for the dominant enantiomer. Absolute configurations can be established by anomalous dispersion X-ray crystallography (and it is estimated about 11,000 such determinations have been made) or chiroptical spectroscopies. This talk concentrates on the latter, and in particular illustrates how electronic circular dichroism, optical rotatory power, optical rotatory dispersion and vibrational circular dichroism, coupled with powerful modern quantum mechanical simulations of both the spectra and the reaction transition states, can be used to assign the absolute configurations of scalemic molecules. In effect, the QM "chiroptical instrument" is now seen as an indespensible symbiotic component of a modern synthetic laboratory, and the skills needed to operate it properly should be part of the training of any aspiring synthetic chemist who may be making scalemic molecules.
A number of case studies are presented, including several where such QM calculations have in fact reversed previous assignments. These include:
If the audience wishes to inspect the talk, they should come to the lecture with a laptop or other mobile device (with Java, sorry, no iPads yet!), connect to the talk at http://www.ch.ic.ac.uk/rzepa/talks/imperial11/ and follow along.