The Sceptical Chymist | Reactions: Henry Rzepa

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Henry S. Rzepa is professor of computational chemistry at Imperial College London. Trained as a physical organic chemist, he adopted the use of computers to try to get answers to deep questions in molecular behaviour at a time when a molecule with more than about 40 atoms was considered unreachable in this manner. His research, which nowadays covers unravelling on a computer the mechanisms of catalysed reactions and polymerisations, is balanced by his interest in using new mediums such as the Internet to communicate this science both visually and in a data-rich manner. He also writes a blog where he explores some of the interesting nooks and crannies of chemistry.

1. What made you want to be a chemist?

Bright colours! Chemistry sets for 12 year olds in my time were colourful play-things, and I soon discovered that the diazo-coupling reaction could produce vivid hues. I became more adventurous, culminating in my making benzidine (I was oblivious at the time to how carcinogenic this substance is), which also produces lovely colours when diazo-coupled. On the 50th anniversary of my making this molecule, I decided to take a look at the mechanism of the reaction that produces benzidine, via the so-called benzidine rearrangement. I have to say that reaction mechanism has a decidedly modern feel to it nowadays, and it reveals how much chemistry has actually changed in 50 years.

2. If you weren’t a chemist and could do any other job, what would it be – and why?

I have come to realise that art and science are just different aspects of the same. Science can be artistically creative, and so I do sometimes wonder if I could have succeeded as a creative artist. I would love to have developed musical skills, but at the age of 13 they were distinctly lacking and so I became a chemist. Also, when giving lectures to undergraduates, I do often wonder how different that experience would be to say doing a musical gig to an audience.

3. What are you working on now, and where do you hope it will lead?

Quantum chemistry can now model both molecules and their reactions to remarkable accuracy, an extraordinary change compared to when I started in chemistry. One can now genuinely (thins means meaningfully) explore a reaction computationally as a prelude to undertaking it in practice. We, with collaborators, are looking at the stereochemical outcome of reactions induced by organocatalysts or metals (e.g. Ag, Mg, Zn, etc) to see if we can pin down the origins of their selectivity. I think that with the theoretical advances made over the last 30 years, coupled with the incredible increase in available computing power, it will become the norm for virtually any type of chemist to synchronously explore their chemistry on a computer as well as in the laboratory. But in fact, what I have noticed is that doing this more often than not brings entirely unexpected surprises. There is still lots to discover about molecules and their chemistry.

4. Which historical figure would you most like to have dinner with – and why?

Francis Crick (is he too recent to be historical?) Or Archimedes.

5. When was the last time you did an experiment in the lab – and what was it?

Well, it was more recent than the benzidine rearrangement done 50 years ago. Some 20 years ago I used to love shimming NMR spectrometers, and I measured many an interesting spectrum using many an interesting pulse sequence. Of course, I presume the question means what a chemist might call a “wet” experiment in a wet laboratory, and not an “in silica” experiment on a computer. But as I imply above, these two very different sorts of experiment are indeed merging and sitting side by side nowadays. Perhaps the closest to a real recent experiment involved the electronic circular dichroism spectrometer at the Diamond light source at Didcot, in which I participated a few months ago. We were measuring the ECD of a thin film, to try to establish what the structure of a natural product was. I did not actually press the buttons, a colleague did (but I pressed them in spirit). This is perhaps the best example of synergy between experiment and theory. Having obtained the ECD spectrum, one truly has to then compute the spectrum theoretically in order to get a proper understanding of the molecule.

6. If exiled on a desert island, what one book and one music album would you take with you?

Is that question not copyright? I love reading biographies, and so a nice compilation of the 50 greatest scientists would do nicely. With album, we again hit the phenomenon of changing semantics. Is an album nowadays a playlist? Surely it cannot refer to the physical object we used to call a vinyl album? You see, another interest of mine is the semantics of chemistry, and how to implement this on the Web, and so I do linger on definitions sometimes. Even the question; what would you load up onto your iPod is also out of date. Nowadays it would be “what would you have on the cloud?” OK, if you are really asking what kind of music do I like, I would have to tell you either Sibelius or the Irish fold band the Dubliners. Come to think of it, these comments also relate to “the one book”. Curiously, I was invited yesterday to participate in a half-day symposium on recent advances in teaching, and am thinking of a title along the lines of “Wither the book? (the “h” may or may not be included in the first word at your inclination). What does a book mean nowadays? What should it become? Does it have boundaries any more? (boundaries which used to be defined by its bindings). Should one press the “3D print” button on a book of the future? Etc.

7. Which chemist would you like to see interviewed on Reactions – and why?

Has Roald Hoffmann been interviewed? He wonderfully sits in the land joining science and art. Or Paul Schleyer, who also straddles wide swathes of chemistry, but in a very distinctly different way from Hoffmann.

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