Transcript of an interview with
Prof. Leslie Leiserowitz (Weizmann Institute of Science)
at the Stockholm Town Hall
Saturday, September 14, 2002
Well, Leslie, as we sit here in front of the Stockholm Town Hall, the site of the Nobel Prizes, I think about your work on the tetraphenylbutatriene, which I talk about each year in my course. We just talked about it last Friday.
I’d like you to say a few words about how you came to study that compound and what you were looking for.
Well, I’m not sure whether I recollect it all exactly, but at that time Meir  was very interested in solid state reactions involving C-C double bonds, and we at the time, on the other side, were also interested in electron densities, but also electron densities from the point of view that we wanted to see lone pair electrons, etc.
Now, Phil Coppens  some years prior to that had studied the triazine and he had been able by low-temperature x-ray diffraction to establish the lone-pair density of the nitrogen atom.
So we thought perhaps in order to convince the stereochemists and others that people measuring deformation electron density do yield meaningful results, it would be nice to show the electron density of neighboring C-C double bonds in the diene or triene, because according to theory, the electron pi lobes should be perpendicular to one another.
Was this a sophisticated theory at the time, or just sort of a qualitative theory that suggested that that the double bonds should be perpendicular when they are successive to one another?
Well, we thought it was a well-established theory, because it is certainly known that in dienes the planes of the systems are perpendicular, you know. You have the carbon atoms just apart and you can see that the system is perpendicular to one another. And so it was well established as far as we were concerned.
So we went ahead with the low-temperature study on tetraphenylbutatriene.
But I think I should say one more thing. We had an internal check. There were several aromatic bonds which were chemically identical but crystallographically different. So we had an internal check as to how good the data was.
So actually the purpose of this experiment was to confirm theory, but also to establish the technique and its ability to show what bonds really were.
Yes, that’s exactly correct. That’s quite so. It was also to establish a technique and to show other people that it was a technique that was worthwhile applying.
But moreover we had other ideas then. It was in 1971. I had come here in fact, to Uppsala, to do an experiment to prove the existence of a C-H with triple bond interaction. We did that with propiolic acid - the cis structure.
We wanted to get also hold of the electron density distributions of the C-C single bond, the C-C double bond, C-C triple bond. And in butatriene, as I recall, the central bond does have some triple bond character, and so we tried to kill two birds with one stone
Great. Thank you very much.
So you see, Stockholm is a beautiful place, but we’re still working. Say hello to the students in Chemistry 125.
Hi folks. I hope it wasn’t as clear as mud, but it’s for you to decide. Thank you very much.
 Prof. Meir Lahav, a physical-organic chemist, is a long term collaborator of Prof. Leiserowitz, with whom he shared the Aminoff Prize - which was the occasion of our being together in Stockholm. Lahav had been particularly interested in reactions where two double bonds, side by side, react to form a four-membered "cyclobutane" ring. Reaction between the central bonds of two butatriene molecules would have given a cyclobutane in which each carbon was also a member of a double bond directed outward from the ring. The reaction did not work.
 By "on the other side" Leiserowitz is indicating that his main research focus has been on determining structure by x-ray diffraction, not studying organic solid-state reactions for their own sake. A special strength of the Lahav/Leiserowitz collaboration has been the way their individual strengths complement one another.
 Prof. Philip Coppens of the University at Buffalo, was a graduate student together with Leiserowitz under Professor Gerhardt Schmidt at the Weizmann Institute. He has carried out a number of important high-precision studies of electron density in crystals.
 It was important that any differences in the shape of the bond cross section should be clearly real and not due to an error in the measurements. How similar the cross sections were in four independent phenyl rings would help evaluate how large experimental error in the experiment might be.