Henry Rzepa, talks and Presentations Henry Rzepa

A history of symmetry, stereochemistry and how the Woodward-Hoffman rules for pericyclic reactions came about.

The future of the chemistry textbook, and how disruptive technologies and social media might impact upon it. The talk is available at http://www.ch.ic.ac.uk/rzepa/talks/imperial13/

Changing ways of sharing research in Chemistry

In 1994 onwards, the Internet was seen as having an increasingly influential potential for how chemistry may be handled, shared, stored and communicated, and how the Internet might have impacted upon the quality, reproducibility and re-use of both experimental observation and computational modelling for new scientific opportunities. Examples will be presented to illustrate from a personal viewpoint how the author carried out collaborative research in pre-Internet days, and how things have changed up to 2012. This will include a review of early attempts at electronic conferencing, examples of modern "datuments" as data-enriched interactive articles, the role of digital repositories and how environments such as blogs and Wikis can be used to promote collaborative new science.

The first part of the talk will cover the essential features of modern chiroptical spectroscopies, and the second will illustrate these with several case studies. These will include the rather controversial histories of the determination of the absolute configurations of an important series of sulfur-containing natural products such as the dethiochaetocins and dehydrogliotoxins. The mechanism of dethionation of these species has been claimed to involve both retention and inversion of configuration at the carbon-S centre, and a possible route for either process is shown in the scheme below. Computational chemistry is also used to chart the viability of such a mechanism, although the techniques used to do so require methods that have only recently been introduced as routine procedures. The take-home message is intended to illustrate that the use of computational modeling for both chiroptical spectroscopy and associated mechanistic exploration is increasingly regarded as a sine qua non of the synthetic laboratory.

Of the 61M 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, can be used to assign the absolute configurations of scalemic molecules. In effect, the QM "chiroptical instrument" is 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.

I venture to suggest that ... the general development of the human race to be well and effectually completed when all men, in all places, without any loss of time, at a low rate of charge, are cognizant through their senses, of all that they desire to be cognizant of in all other places. ... This is the grand annihilation of time and place which we are all striving for, and which in one small part we have been permitted to see actually realised" (Samuel Butler, 1863, [1])