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00:00:29 Born in 1937 in Złoczów, Poland,

00:00:32 Roald Hoffman survived the Nazi occupation in Europe

00:00:35 before emigrating to the United States in 1949 at the age of 11.

00:00:40 Hoffman attended schools in Czechoslovakia, Austria, and Germany

00:00:44 and learned four languages while moving from one displaced person's camp to another

00:00:49 with his mother and stepfather.

00:00:51 After arriving in the United States,

00:00:53 Hoffman completed his primary education in Brooklyn

00:00:56 and graduated from Stuyvesant High School in 1955.

00:01:00 Enrolling in Columbia University on a Pulitzer Free Scholarship,

00:01:04 Hoffman graduated summa cum laude in 1958 with a B.A. in Chemistry.

00:01:09 He then obtained an M.A. in Physics in 1960

00:01:13 and a Ph.D. in Chemical Physics in 1962 from Harvard University.

00:01:18 Under the joint supervision of Martin Guterman and William Lipscomb,

00:01:22 Hoffman's thesis work was on molecular orbital theory of polyhedral molecules,

00:01:27 particularly boron hydrids,

00:01:29 and the application of second quantization methods

00:01:32 to the study of excited states of helical polymers.

00:01:35 From 1962 to 1965,

00:01:38 Hoffman remained at Harvard to serve as a junior fellow in the Society of Fellows.

00:01:43 He then joined the faculty of Cornell University as an associate professor,

00:01:47 earning a full professorship in 1968.

00:01:50 He became John A. Newman Professor of Physical Science in 1974.

00:01:55 Roald Hoffman has received many awards during his career.

00:01:59 Most notably, he shared the Nobel Prize in Chemistry in 1981 with Kenichi Fukui

00:02:04 for his work with R.B. Woodward on the principles of orbital symmetry conservation.

00:02:09 In the following program,

00:02:11 Roald Hoffman is interviewed by his longtime friend and colleague,

00:02:15 Dr. Andrew Streitweiser, Jr.

00:02:18 I'm Andrew Streitweiser, Jr.,

00:02:20 Professor of Chemistry at the University of California, Berkeley.

00:02:23 I'm talking today with Roald Hoffman,

00:02:26 the John A. Newman Professor of Physical Science

00:02:29 in the Chemistry Department at Cornell University.

00:02:32 Professor Hoffman is a theoretical chemist

00:02:36 who has changed the way that organic chemists think about their science.

00:02:40 In fact, chemists generally, the way they think about their science.

00:02:44 He's received many honors for his work,

00:02:47 including the ACS Award in Pure Chemistry.

00:02:50 He shared the Cope Award in Organic Chemistry

00:02:53 with Professor Woodward in 1973.

00:02:56 In 1981, he shared the Nobel Prize with Kenichi Fukui.

00:03:00 And last year, 1982,

00:03:03 he also received the ACS Award in Inorganic Chemistry,

00:03:07 the only person so far to have received both the Cope Award in Organic Chemistry

00:03:12 and the ACS Award in Inorganic Chemistry.

00:03:15 In 1958, you went to Harvard University for your PhD.

00:03:21 Yes, I went in 1958,

00:03:25 I think driven or inspired to study theoretical chemistry

00:03:30 by the first really good courses that I had at Columbia,

00:03:33 which were in that field,

00:03:35 plus being good at mathematics.

00:03:38 But I think I was really interested in chemistry all along.

00:03:42 And I went in 1958 to Harvard,

00:03:46 and I wanted to work with Bill Moffat,

00:03:49 who was the leading theoretician of his time,

00:03:54 generally acknowledged to be the best young theoretician.

00:03:57 He was only 33 at that time.

00:03:59 Died at a very young age, very tragic.

00:04:02 In fact, I had signed up to work with Moffat

00:04:04 when he died in December of that year, 1958.

00:04:09 And then there were a number of us

00:04:12 who were left stranded without anyone to work for

00:04:17 because Harvard at that time did not have anyone else in theory.

00:04:21 Wright Wilson did not do any theory at that time.

00:04:24 Lipscomb and Karplus and Roy Gordon had not yet appeared on the scene.

00:04:28 Lipscomb came two years later, and eventually I switched to him.

00:04:31 The young postdoc of Moffat's, Martin Guterman,

00:04:34 was made an instructor and then an assistant professor.

00:04:37 And the day he became an instructor, he got four graduate students,

00:04:41 which was myself, Bob Fulton, Ron Felton.

00:04:45 Bob Fulton is at Florida State,

00:04:47 Ron Felton at Georgia Tech,

00:04:49 and Georges Vanier, who was in Zurich, University of Zurich.

00:04:53 And so we had immediately a little theoretical group.

00:04:56 I began work with Martin.

00:04:59 Martin put me at one point on an experimental project.

00:05:04 I was actually pretty good at experimental work,

00:05:06 and the first two papers I've published were experimental ones

00:05:09 from work at the National Bureau of Standards in Brookhaven.

00:05:14 I have a paper in review of scientific instruments

00:05:18 from some work at Brookhaven.

00:05:20 But I had not done any work for a while.

00:05:23 Martin put me to synthesizing some porphyrins,

00:05:27 and I sealed up some pyrrole in a bomb,

00:05:30 and I didn't seal the bomb very well,

00:05:32 and I put it in a heater.

00:05:34 And one day, one evening, while it was heating,

00:05:36 it exploded, spattering brown gunk all over the walls

00:05:40 of newly opened Conant Hall.

00:05:43 Vanelli was very angry at me,

00:05:46 and that was the end of my experimental career,

00:05:49 at least for a while.

00:05:51 I began work with Martin Guterman

00:05:54 on some theoretical work on porphyrins.

00:05:57 I remember also learning group theory at that time.

00:06:00 I actually learned it in a summer school in Sweden,

00:06:04 one of Per Olof Lundin's famous summer schools

00:06:08 in the summer after my first year of graduate school,

00:06:11 where I first encountered group theory.

00:06:14 I went back, and with having learned the group theory,

00:06:18 and someone at that time at Harvard

00:06:22 was talking about making cubane.

00:06:25 So I said, I'll do a calculation on cubane.

00:06:29 And I went ahead, and I put 8 orbitals

00:06:34 on 8 corners of a cube.

00:06:38 I wasn't thinking very hard, so what I put were s orbitals.

00:06:41 And I did the group theory for 8 s orbitals

00:06:44 at the corners of a cube, and I went to Martin Guterman

00:06:47 and said, here, I've done a calculation on cubane.

00:06:50 Look what happens.

00:06:51 It's really simple.

00:06:52 Group theory factors the levels into 1, 3, 3, and 3,

00:06:58 and it's all easy to do.

00:07:00 And he looked at it for a while, and he said,

00:07:02 what you've really done is 8 hydrogen atoms

00:07:04 at the corners of a cube.

00:07:05 That's not cubane.

00:07:06 Go back and do cubane with all the p orbitals

00:07:09 and on the carbons.

00:07:12 And I did that, and then I set up a matrix 30 by 30

00:07:17 for the 8 times 4 valence orbitals on a carbon,

00:07:24 plus the 8 hydrogens.

00:07:27 Sorry, 40 by 40 it is then.

00:07:30 That's right, 8 carbons and 8 hydrogens.

00:07:34 And I could not solve it, and I let it lie for a while.

00:07:37 But that was the beginning, and perhaps a plant in my mind

00:07:41 of eventually doing something about a problem

00:07:44 of that magnitude.

00:07:45 And it wasn't until two, three years later,

00:07:48 after I had been in Russia and I had switched to Lipscomb,

00:07:52 that I was able, in fact, to program a method

00:07:56 for doing this.

00:07:57 And that was the beginning of the extended Hickel theory.

00:08:01 It's interesting how the things that led up to this,

00:08:04 there had to be a cubane molecule in the air.

00:08:08 I had to know some group theory and to first make

00:08:11 a naive mistake about thinking that cubane is 8 hydrogen atoms

00:08:17 and somehow letting the problem rest for a while

00:08:20 and eventually coming back.

00:08:22 But now you spent this period, a summer period,

00:08:27 in the summer school in quantum chemistry,

00:08:31 and you also spent a while in Russia.

00:08:33 Yes.

00:08:34 Both of these were most unusual for graduate education.

00:08:37 Tell us how they came about.

00:08:40 Well, I think the summer school in Sweden,

00:08:44 that was a new exciting thing at that time,

00:08:47 well advertised.

00:08:50 People knew about it.

00:08:52 It was only the second year of that school.

00:08:54 The first one had been held in 1958,

00:08:57 and this was the second one in 59.

00:08:59 I went there.

00:09:01 I got a scholarship from Lev Dean,

00:09:04 and I spent a whole summer traveling around Europe

00:09:08 while I was going to that school.

00:09:10 It was a remarkable place.

00:09:12 I came back extremely enthusiastic about formalistic quantum chemistry

00:09:18 because that's what I learned in Lev Dean School.

00:09:20 I learned about projection operators.

00:09:22 I learned about group theory.

00:09:25 And for a while, Martin Goodman reminds me,

00:09:28 I used to go around giving seminars on projection operators

00:09:31 and about the more formalistic side of the quantum chemistry,

00:09:36 but somehow underneath it was a background

00:09:41 and a commitment to chemistry

00:09:44 so that I was not, in fact,

00:09:46 converted by this extremely important educational experience

00:09:50 to being a formalistic theoretician.

00:09:53 I could have gone that way at that point

00:09:56 because the instruction in that school led in that direction.

00:09:59 Something kept me in chemistry at that point.

00:10:02 I think just the beginnings of an interest I've always had

00:10:07 in the complexity of molecules, in shapes,

00:10:11 just the fact that I was interested in cuban,

00:10:13 a little later in boron hydrides,

00:10:15 a very basic interest in molecular shapes

00:10:18 kept me from succumbing, if I can put it that way,

00:10:22 to more formalistic theory.

00:10:25 The Russian experience was something different.

00:10:28 One of the things motivated,

00:10:32 Michael Kasha came to Harvard in 58, 59

00:10:37 and gave a series of lectures about exciton theory

00:10:41 and about Davidoff.

00:10:43 The work had come from Russia

00:10:45 about energy transfer molecular crystals

00:10:48 and Kasha was propagandizing it, using it,

00:10:51 and he made it sound very interesting.

00:10:55 I don't know how exactly I got into my head to go to Russia,

00:10:58 but I've always been interested in Slavic languages

00:11:04 and I speak Russian, I've kept up my Russian,

00:11:07 I'm very interested in Russian language and literature.

00:11:10 I somehow got it into my head

00:11:12 that it would be an interesting thing to do.

00:11:14 I suspect there may have been some other personal factors

00:11:17 that I wasn't quite sure about what I wanted to do my PhD research on

00:11:22 and maybe that was a year, a possible year off.

00:11:26 I studied Russian intensively at Indiana University for a summer

00:11:31 and after that went for nine months to Moscow University

00:11:35 to work with Davidoff.

00:11:37 That was also only the second year

00:11:39 of a US-Soviet exchange of graduate students.

00:11:42 I didn't get much work done.

00:11:44 I published one paper in Russian,

00:11:47 and the cultural experience was an incredible one.

00:11:52 I never saw so much ballet and opera as I did in Russia

00:11:56 and just having to cope with a foreign language,

00:11:59 at that time that was foreign to me,

00:12:02 and a different culture was an exciting thing.

00:12:06 I was also just married.

00:12:08 My wife, whom I had met in Sweden,

00:12:11 came in April over here to get married

00:12:15 and in September we went off to Russia.

00:12:18 I've always said that's our honeymoon.

00:12:20 It's been our honeymoon in Russia.

00:12:22 For her it was an even greater cultural shock

00:12:25 to move from Sweden to the United States

00:12:27 then to the Soviet Union for a year.

00:12:29 But I came back just full of enthusiasm.

00:12:32 Actually, I came back with a feeling that I should,

00:12:36 with a feeling that the problems that I wanted to do

00:12:39 could be probably solved with a computer

00:12:42 and computers were just coming up.

00:12:44 Lipscomb 650 was what we used at that time.

00:12:47 As I switched to Lipscomb and as we began to program

00:12:51 this extended Hickel method,

00:12:54 it seemed that I had acquired a lot of pent-up mental energy

00:12:59 which was released in that one year.

00:13:01 So I did all my PhD work.

00:13:03 That one year I came back.

00:13:06 I don't think I was set back by that year.

00:13:10 I do see the point that it is an intense experience

00:13:13 to go to school.

00:13:14 One has to concentrate.

00:13:16 But certainly I would advise kids to go off somewhere

00:13:20 in college a summer to go to Europe

00:13:24 to learn a foreign language.

00:13:26 It's a very broadening experience,

00:13:30 a very important cultural experience,

00:13:32 especially for Americans to go somewhere else.

00:13:37 Well, then because of this,

00:13:40 I suppose it wasn't necessary for you to go to Europe

00:13:43 for a post-doctorate.

00:13:46 No.

00:13:49 When I got my PhD in 1962,

00:13:52 1962 was not a bad time to go out looking for a job.

00:13:55 There was an explosion in science education in general.

00:13:59 Departments were growing.

00:14:02 I applied at a number of places for assistant professorships

00:14:05 without doing a post-doc and I got lots of offers,

00:14:08 including from Berkeley at that time.

00:14:11 But I decided to stay on at Harvard as a junior fellow,

00:14:15 which was a period of three years

00:14:21 that allowed me to do,

00:14:25 allowed one to do whatever one wanted to do.

00:14:28 A select group of eight or so people were chosen each year,

00:14:33 interesting organizational society fellows.

00:14:36 Bob Woodward himself was a member,

00:14:38 and Bright Wilson, Dudley Hirschbach,

00:14:41 a number of the people that we know

00:14:43 were members of this society of fellows in their time.

00:14:47 And it is in this period, 1962 to 1965,

00:14:50 that I began to switch toward organic problems,

00:14:56 and it was in that period that that very important collaboration

00:14:59 with Bob Woodward began.

00:15:01 What's your feeling or thinking about the kind of background

00:15:05 that most theoreticians get?

00:15:08 Is it too heavily weighted toward physics?

00:15:11 I don't know.

00:15:16 There is something that happens to chemistry students

00:15:23 around the junior year in college

00:15:25 when they take a physical chemistry course,

00:15:28 which seems to partition them

00:15:30 into those who like the abstract mathematical way of thinking about things,

00:15:37 who like physical chemistry,

00:15:39 and then go on to become experimentalists in physical chemistry or theorists,

00:15:43 and other people who prefer a different type of complexity.

00:15:51 Well, some split seems to set in at that point.

00:15:56 I think I fell into the physical chemistry line at that point.

00:16:01 I suspect had I had an inspiring organic teacher at Columbia,

00:16:07 I would have probably become an experimental organic chemist,

00:16:10 but I didn't.

00:16:13 I kept up an interest in chemistry,

00:16:17 and it was continually encouraged

00:16:24 and heightened by being associated with Lipscomb.

00:16:29 Lipscomb stressed the importance of structure.

00:16:35 Of course, he was a crystallographer, so that was clear.

00:16:37 We were in rooms, even those of us doing theory,

00:16:39 like Russ Pitzer and Bill Kern and Larry Lohr and myself,

00:16:43 we were in rooms with crystallographers.

00:16:45 Structures were flowing through that place.

00:16:48 And furthermore, the structures of the boron hydrides,

00:16:51 and I was the only one actually who worked at that time

00:16:56 on the electronic structure of the boron hydrides,

00:16:58 but just the structures that were around us were sufficiently complicated.

00:17:02 They were these polyhedral molecules, these fragments of an icosahedron.

00:17:06 They were sufficiently complicated that after having thought about boron hydrides,

00:17:11 organic chemistry seemed simple.

00:17:14 And so when I did get interested in organic chemistry,

00:17:18 which was after my PhD and in that period of the junior fellowship,

00:17:23 and with the encouragement of E.J. Corey at an important stage,

00:17:28 when I did become interested in organic chemistry, it was just beautiful.

00:17:32 The world opened up to me once again,

00:17:34 and I learned very quickly about structure and reactivity.

00:17:39 It was wonderful.

00:17:41 I'd like to ask you about how you got into this development

00:17:45 of a relatively simple theory that required lots of approximations

00:17:50 to understand complex structures.

00:17:55 Well, I was forced to it because the boron hydrides were

00:18:03 essentially and irreducibly three-dimensional.

00:18:08 That is, I knew Hickel theory for pi electron systems,

00:18:15 and incidentally it was your book that played, of course,

00:18:19 a remarkable pivotal role, not only for me but for other people,

00:18:23 by showing us what you could do with simple Hickel theory.

00:18:27 We knew about it from other places.

00:18:29 People had written papers, but that book was unique in its time.

00:18:34 But it focused interest on pi electron systems,

00:18:38 and people who were doing simple empirical calculations

00:18:41 did them on pi electron systems.

00:18:44 But here I was working with Lipscomb on boron hydrides,

00:18:47 and I just had to do something about the electronic structure,

00:18:50 and it was clear that we had to get in the s and the p orb.

00:18:54 We had to get in the sigma system of the molecule.

00:18:57 So almost without thinking about it, driven by the complexity of the problem,

00:19:02 we did something and we developed this extended Hickel method.

00:19:06 We could only do it when computers became available

00:19:09 because we were solving secular determinants

00:19:12 which were not easy to do by hand.

00:19:15 So the availability of computers fed into this.

00:19:20 A knowledge of group theory and symmetry fed into this,

00:19:24 and I think the seeds of my subsequent interest

00:19:28 and applications of symmetry,

00:19:30 for instance, in orbital symmetry in the organic realm,

00:19:34 the seeds of that are in thinking about something like B12H122-,

00:19:40 about an icosahedral molecule,

00:19:42 and learning to be familiar with group theory to use it.

00:19:47 I did learn also, I think, in Lipscomb's group and from Gutermann,

00:19:54 how to make approximations.

00:19:56 One interesting thing that came out of the Porphyrin work

00:19:59 was that it's a rather complicated technical thing,

00:20:02 but there is one model for the porphyrins,

00:20:05 which goes back to John Platt and Martin Gutermann,

00:20:08 which involves just a cyclic polyene

00:20:11 and the real porphyrin ring being a perturbation on a cyclic polyene,

00:20:15 which has greater symmetry than the porphyrin really does.

00:20:19 And so there is a pseudo-symmetry at work.

00:20:23 There's a higher symmetry that's approximate

00:20:26 and a real symmetry that's lower.

00:20:30 Well, that kind of thinking of, if one could say it,

00:20:34 not taking symmetry too literally,

00:20:37 but thinking about the underlying pseudo-symmetry behind this,

00:20:41 which was an important element.

00:20:44 It taught me to make approximations,

00:20:47 but somehow that behind them there would be some essence

00:20:51 based on symmetry and that I should look for it.

00:20:56 I must say that really the turning point

00:20:59 was the experience of working with Woodward subsequently,

00:21:03 even as far as my interest and the way I treated theory,

00:21:10 because even though I was interested in chemistry

00:21:13 and even though I had a good appreciation of symmetry,

00:21:16 when I was working for my PhD,

00:21:19 and in the immediate year or two afterwards as a junior fellow,

00:21:23 as I developed the extended Hickel method,

00:21:26 which initially was developed in the Lipscomb group

00:21:29 with Lipscomb and with Larry Lohr,

00:21:32 and all three of us worked together on this really,

00:21:36 as I began to do calculations on organic molecules,

00:21:40 I was still largely operating in the mode of a calculator.

00:21:45 I was not too well, badly, calculating observables.

00:21:52 You can see that in the papers.

00:21:54 The papers are full of tables of numbers.

00:21:57 I was interested in something which was true,

00:22:01 it was structural, like the energy difference

00:22:03 between chair and both cyclohexane,

00:22:05 or between cis and trans butene too.

00:22:07 So that's the kind of thing I focused in,

00:22:09 but I was not focused in on the explanations,

00:22:12 on why those differences were there.

00:22:15 But that was common in the theory of the time.

00:22:17 It was.

00:22:18 The focus on numbers and relating the numbers

00:22:21 and energies to experiment.

00:22:23 It still is to some extent,

00:22:24 and having better calculations hasn't changed anything,

00:22:27 because having better calculations focuses you in still more on the numbers,

00:22:32 and the computer is psychologically addictive as it is anyway,

00:22:36 so that you are led away from explanations.

00:22:42 It was really the experience of working with Woodward

00:22:45 and producing a simple explanation

00:22:49 in terms of one orbital or a subset of orbitals,

00:22:53 and seeing the impact that this portable explanation,

00:22:57 this explanation that people could take away,

00:23:00 a symmetry based,

00:23:01 seeing the impact of this on the community,

00:23:05 that led me subsequently, I think,

00:23:07 to in fact change my style of doing theoretical chemistry

00:23:12 so that even when I was doing calculations

00:23:17 far away from that particular impetus or instance of the orbital symmetry,

00:23:23 I had become transformed in some way from just a calculator

00:23:28 to more of an explainer, a seeker for explanations.

00:23:33 And perhaps there were seeds of that before,

00:23:36 but that transformation, I think,

00:23:38 can be traced fairly well to the impact of the orbital symmetry work.

00:23:42 This is an impact that the orbital symmetry work had on me

00:23:45 and my scientific style.

00:23:48 Well, I remember Woodward spoke often in various talks

00:23:53 of his identifying several key examples

00:23:57 of the many examples one could have picked from the literature.

00:24:01 He had picked on three or four key examples

00:24:05 of very strange stereochemical phenomena

00:24:08 in openings of rings and the like,

00:24:11 and he knew that or realized that there was something

00:24:14 that was involved in these systems

00:24:16 that had to do with their underlying electronic structure,

00:24:19 but couldn't quite put his finger on what it was.

00:24:22 And did he come to you with this problem for an explanation?

00:24:26 How did you get together on this?

00:24:29 Well, no, he didn't come directly to me.

00:24:33 It's a longish story,

00:24:38 which I've talked about a little bit

00:24:41 in the lecture I gave at Woodward Symposium

00:24:44 in 1981 summer at the ACS meeting.

00:24:48 But what happened was that he, in fact,

00:24:53 needed a crucial transformation

00:24:57 in the vitamin B12 synthesis.

00:25:01 He needed to affect a certain transformation,

00:25:04 which now we would call an electrocyclic reaction.

00:25:07 And he, from steric grounds,

00:25:11 came to a conclusion which was opposite to the experimental result

00:25:15 in arguing about the stereochemical course of this reaction.

00:25:18 And so it was a puzzle.

00:25:20 Other work drifted in key observations, puzzling observations

00:25:24 from work of Fogel and Kriege.

00:25:26 And he posed that problem to a number of people around.

00:25:30 I first heard about it when Doug Applequist,

00:25:35 who was visiting from Illinois at Harvard,

00:25:40 and with whom I talked a lot,

00:25:42 from whom I learned a great deal about strained rings,

00:25:45 told me one time about this problem

00:25:48 that Woodward had posed at one of his famous evening seminars.

00:25:56 And it was the problem of the stereochemistry

00:25:59 of what we now call an electrocyclic reaction.

00:26:02 Apparently, those evening seminars, which were famous,

00:26:06 they went on all evening, began innocuously

00:26:09 with someone talking about some problem

00:26:12 and eventually ended up with a monologue by Woodward

00:26:15 about everything under the sun.

00:26:17 I still was not an organic chemist.

00:26:20 I didn't go to those.

00:26:23 In fact, let me digress for a moment.

00:26:25 I did not talk to Woodward

00:26:29 until some five years after I had begun Harvard.

00:26:33 He was a famous man you saw in the corridors.

00:26:35 He didn't teach any courses.

00:26:37 He was not terribly accessible.

00:26:40 He was busy, and you didn't bother him,

00:26:43 although you saw him around.

00:26:45 I went and talked to Woodward once

00:26:47 after I had written the first extended Hickel paper.

00:26:50 Perhaps he knew I existed,

00:26:52 but I really did not have a dialogue with him

00:26:55 until well into my fifth year after I had finished my PhD

00:27:02 and when I was a junior fellow.

00:27:05 Anyway, Doug Appelquist brought this problem to me

00:27:08 and said, hey, Woodward, at his evening seminar,

00:27:11 has suggested an orbital explanation

00:27:16 for why butadiene cyclizes in a certain way to cycloputene

00:27:23 or hexatriene does it in another way

00:27:25 and why these change as they go from a thermal

00:27:28 to a photochemical reaction.

00:27:31 And he asked me, what do you think about it?

00:27:33 I was still in my calculator phase then,

00:27:37 and what I said is, I'll do a calculation on it.

00:27:41 I didn't want to think about the simple explanation.

00:27:44 Woodward had in fact come up at this seminar,

00:27:48 and he had come up independently,

00:27:50 with the first simple orbital explanation

00:27:54 in terms of the nodal properties of the highest

00:27:57 occupied molecular orbital.

00:27:59 I did some calculations on it, and sure enough,

00:28:01 I found first of all that there was

00:28:03 a preferred mode of a conrotatory mode

00:28:07 for the butadiene, a disrotatory mode

00:28:11 for a thermal hexatriene reaction.

00:28:14 I found that this was preferred, and you see,

00:28:18 in order to do that, I had to have the tools

00:28:22 at my disposal.

00:28:23 I couldn't have done that calculation

00:28:25 had I not had the extended Hickel method available to me

00:28:28 so that within a day or two I could do that.

00:28:31 And knowing enough organic chemistry that you knew

00:28:33 what all these structures were.

00:28:35 That's right.

00:28:36 Everything blended together in some way.

00:28:39 I did the calculation.

00:28:40 I found Woodward's explanation was substantially correct,

00:28:44 and there the matter rested for a few weeks

00:28:47 until one time after a seminar by Bill Dering,

00:28:51 Woodward and I happened to be near the blackboard,

00:28:54 and he spoke to me for the second time in now

00:28:57 about five and a half years at Harvard,

00:29:00 and he asked me...

00:29:02 Dering was talking about electrocyclic reactions.

00:29:05 He even had, rather amusing, there were words even

00:29:09 around for describing what we now call

00:29:11 conrotatory and disrotatory.

00:29:14 Dering called them domino and antidomino,

00:29:17 like a stack of dominoes falling over.

00:29:20 And he was talking about these things.

00:29:22 I came up to him afterwards, and Woodward was there,

00:29:25 and Woodward asked me,

00:29:29 what do you think about this reaction?

00:29:32 This was a few weeks after I'd done the calculations,

00:29:34 and there was never a better prepared young man

00:29:38 to answer the question.

00:29:40 So I told Woodward about our calculations,

00:29:42 and that was the starting point of our collaboration.

00:29:46 But everything went into it.

00:29:48 Having extended Hickel around,

00:29:50 talking to organic chemists,

00:29:52 having had the background of getting interested

00:29:55 in organic chemistry through E.J. Corey,

00:29:59 having the background of complexity from Lipscomb,

00:30:05 and the knowledge of symmetry and orbitals from Gutterman.

00:30:08 I think all of these things came together.

00:30:12 I think nothing ever is completely original or unique.

00:30:17 There are sources for these things which can be traced.

00:30:21 Except that, what were the traces?

00:30:25 I guess the traces of Woodward's thinking

00:30:29 of the frontier orbitals,

00:30:32 did he know about Foucault?

00:30:34 Or had he heard of Foucault?

00:30:36 No, I don't think so.

00:30:39 I don't think that Woodward knew about Foucault.

00:30:43 I don't think much of the world community knew about Foucault

00:30:47 because he was not that well accepted

00:30:50 by the theoretical chemists or his ideas of that time.

00:30:54 His work was known to some people,

00:30:59 but it did not have an impact on Woodward.

00:31:02 I think Woodward was influenced by Moffat.

00:31:06 I think Woodward and Moffat talked a lot to each other.

00:31:10 Woodward's intuition, as great as he was,

00:31:13 and he had a great intuition about many things,

00:31:18 and many people have remarked on that,

00:31:20 Woodward's intuition about bonding

00:31:23 was largely based on valence bond ideas.

00:31:27 And that was transformed when Moffat came to Harvard.

00:31:34 The two men talked to each other a lot.

00:31:36 I have evidence from conversations with other people,

00:31:38 and you can see the evidence in several things.

00:31:40 One is Moffat's interest in ferrocene,

00:31:44 and Woodward played a role in the assignment

00:31:47 of the correct structure to ferrocene.

00:31:50 Moffat's involvement with the octant rule,

00:31:53 which was initially an empirical conclusion

00:31:56 which Woodward was involved with,

00:31:58 but eventually received a theoretical basis

00:32:00 from work of Moffat and Moskowitz.

00:32:03 After this period,

00:32:05 this was a very stimulating and important period,

00:32:08 the three years of your position at Harvard,

00:32:15 and then you went to Cornell.

00:32:17 Yes.

00:32:18 Why Cornell?

00:32:19 One of the few places that offered me a job.

00:32:22 Berkeley didn't the second time around.

00:32:25 And it's actually interesting to reflect on what...

00:32:28 I don't mean to reflect on a specific Berkeley decision,

00:32:32 but on the factors that went in,

00:32:36 because they have something to do with the sociology of science

00:32:39 and attitudes toward applied theory and theory.

00:32:43 In 1962, when I was looking for a job,

00:32:45 I had job offers from everywhere.

00:32:47 It was a good time, as I said, to look for a job.

00:32:51 I had offers from lots of places,

00:32:53 from Caltech, from Berkeley, from Cornell,

00:32:57 and I was a promising young theoretical chemist.

00:33:02 By 1964, the end of 1964,

00:33:05 when I was looking for a job again for 1965,

00:33:08 I had been slightly polluted

00:33:11 in the eyes of other theoretical chemists.

00:33:14 I suspect that they perceived me as being

00:33:18 more applied than they had hoped for.

00:33:20 I hadn't become a pure theorist.

00:33:22 I had become interested in organic chemistry.

00:33:24 I had become an applied theoretical chemist.

00:33:27 And whereas the organic chemists knew my work and liked it,

00:33:31 their physical colleagues weren't particularly impressed by it.

00:33:34 And so all those same places which offered me a job in 1962,

00:33:38 with the exception of Cornell,

00:33:41 did not offer me a job in 1965.

00:33:44 And I had a choice between Cornell and Indiana,

00:33:48 and Pittsburgh, I think, and I chose Cornell.

00:33:53 And I think, to be fair to the views of other people,

00:34:00 I think the impact of the orbital symmetry work

00:34:02 had not yet become apparent in 1964.

00:34:06 The first paper wasn't published until 1965,

00:34:08 and the generality of the ideas,

00:34:10 and also my ability to do anything with them

00:34:15 beyond helping Woodward,

00:34:18 because that might have been a perception at that time.

00:34:22 That had not yet been proven.

00:34:24 And so I had not yet proven myself

00:34:29 that I could do something perhaps in the applied field.

00:34:34 And so I could not get a job elsewhere.

00:34:36 I went to Cornell, where I've been very happy ever since.

00:34:41 It's been now almost 18 years that we've been here.

00:34:44 You came to Cornell, but you continued your collaboration

00:34:47 with Professor Woodward for several years after that.

00:34:51 Yes, the first orbital symmetry paper

00:34:54 appeared when I was still at Harvard.

00:34:56 But then I came here and began teaching here,

00:35:00 and we continued our collaboration

00:35:03 during that important year

00:35:05 when those five little communications came out.

00:35:07 But then we began writing our long paper,

00:35:10 which eventually appeared in 1969 in Un Given to Himmi,

00:35:13 and that's that paper with the blue and green orbitals.

00:35:16 We continued work over a period of four years,

00:35:21 over the telephone,

00:35:23 by many trips that I took up to Harvard.

00:35:30 There are interesting things where Woodward and I,

00:35:33 talking to each other over the telephone,

00:35:36 are talking about the stereochemistry

00:35:38 of complicated concerted reactions.

00:35:41 Imagine talking about a vitamin D photochemistry

00:35:44 over the telephone.

00:35:45 And what would be interesting someday

00:35:47 is to collect my notes, my picture of a molecule,

00:35:50 and Woodward's notes.

00:35:52 I don't have one such to show you, but there are some,

00:35:54 where we talk about ketene adding

00:35:57 to some complicated organic molecule,

00:35:59 and we're trying to describe that over the telephone.

00:36:01 We became pretty good at that.

00:36:03 But we continued for about four years

00:36:05 until eventually that paper was written.

00:36:08 Yes, now that period marks a very critical period.

00:36:12 A critical period, the whole change

00:36:14 in the style of theoretical organic chemistry

00:36:18 as it is now practiced.

00:36:23 There was an emphasis, as you pointed out earlier,

00:36:26 in the late 50s and early 60s,

00:36:29 an emphasis on theory getting numbers,

00:36:33 energy values that you could compare

00:36:35 with reactions and structures.

00:36:38 And now a much more emphasis on applied perturbation theory.

00:36:42 And this reflects itself also in your own thinking,

00:36:46 this change in your emphasis on numbers

00:36:49 to more of an emphasis in what the numbers mean

00:36:53 and applications of perturbation theory.

00:36:56 Yes, I found in perturbation theory

00:37:02 an ideal language for discussing complicated things

00:37:07 in terms of simple things.

00:37:09 And so our stock and trade became an interaction diagram

00:37:13 or a Walsh diagram.

00:37:14 Basically, some diagram where you plot

00:37:17 the orbitals of two pieces of a molecule

00:37:20 on either side of the diagram,

00:37:22 and then you put them together

00:37:25 to make the composite molecule in the middle.

00:37:28 Let me actually show you an example

00:37:31 here on a blackboard of what I mean.

00:37:33 For instance, somewhat later on,

00:37:36 I went on to inorganic molecules.

00:37:41 And say I were interested in the electronic structure

00:37:45 of cyclobutadiene ion tricarbonyl,

00:37:50 which is an interesting molecule in which

00:37:52 a rather unstable thermodynamically

00:37:54 and kinetically organic moiety is stabilized

00:37:59 by complexation with a transition metal piece.

00:38:03 Now, when I want to analyze this,

00:38:06 there are several things I could do.

00:38:08 I could do a calculation on a molecule as a whole,

00:38:11 and I could get whatever property I wanted,

00:38:13 the spectrum, dipole moment molecule,

00:38:16 whatever there is.

00:38:17 And in fact, many people have done that

00:38:19 with increasingly better methods of calculation.

00:38:23 With increasingly larger computers,

00:38:25 one can do calculations on this molecule.

00:38:28 But ultimately, those calculations

00:38:30 do not necessarily tell you

00:38:33 what it is that stabilizes, let's say,

00:38:36 the cyclobutadiene,

00:38:37 what makes it possible for us

00:38:39 to have this molecule in a bottle,

00:38:41 whereas we can't have cyclobutadiene

00:38:43 or not much of it in a normal bottle.

00:38:46 And the kind of analysis that I used

00:38:49 to analyze these things

00:38:53 is very much based in the language

00:38:56 of perturbation theory.

00:38:58 One of these interaction diagrams,

00:39:00 what I would do is,

00:39:01 on one side of the diagram,

00:39:03 I would put down the orbitals

00:39:06 of the cyclobutadiene.

00:39:07 And by now, everyone knows,

00:39:10 thanks to your book and to others,

00:39:12 that the orbitals of cyclobutadiene,

00:39:14 the pi orbitals,

00:39:15 the ones derived from the p orbitals

00:39:19 which are perpendicular

00:39:21 to the plane of the molecule,

00:39:23 that they fall into a one, two,

00:39:25 and one pattern.

00:39:26 And cyclobutadiene itself,

00:39:28 where it's square,

00:39:29 would have four electrons

00:39:31 in these pi orbitals.

00:39:32 So that's the organic component.

00:39:34 I don't want to go into

00:39:35 why that's not particularly stable.

00:39:37 On the other side

00:39:38 is the inorganic component.

00:39:40 And again, this is a story

00:39:42 of getting at the orbitals

00:39:44 of the inorganic component,

00:39:45 meaning the iron tricarbonyl here.

00:39:49 That story is a reasonably complicated one,

00:39:52 but as it turns out,

00:39:53 eventually the orbitals reduce

00:39:55 to a rather simple set of orbitals

00:39:58 which happen to be like this.

00:40:01 And the point I want to get across

00:40:05 about perturbation theory

00:40:06 is that we write down

00:40:07 the orbitals of the pieces.

00:40:09 Then we look at the orbitals

00:40:13 and using the rules

00:40:14 of quantum mechanics

00:40:15 of perturbation theory,

00:40:17 we can see

00:40:18 how these orbitals interact.

00:40:20 And in particular in this case,

00:40:21 it turns out

00:40:22 that this pair of orbitals here

00:40:24 and this pair of orbitals

00:40:27 are in fact

00:40:30 able to mix with each other,

00:40:32 able to interact.

00:40:33 And there is a bonding combination

00:40:35 of the two that goes down

00:40:37 and takes up the four electrons

00:40:39 from the two components.

00:40:41 And here is the stabilization

00:40:42 coming out.

00:40:44 The important thing

00:40:45 is not the particular case.

00:40:46 We've done many such,

00:40:47 but the technique

00:40:48 of perturbation theory

00:40:49 made this all possible.

00:40:52 I should say, though,

00:40:54 that with time

00:40:55 and in part

00:40:57 because of the orbital symmetry story,

00:41:02 I learned to take

00:41:04 the perturbation ideas

00:41:08 out of their mathematical formalism

00:41:10 and try to put them into words.

00:41:13 So instead of writing expressions

00:41:15 with lots of summations in them,

00:41:17 I tended to say

00:41:18 two orbitals will interact,

00:41:20 the in-phase combination

00:41:21 will go down,

00:41:23 the overlap will increase.

00:41:24 I learned how to use

00:41:28 simple arguments,

00:41:29 and I think this had an influence.

00:41:32 Much of what I learned

00:41:33 in perturbation theory

00:41:39 I derived, actually,

00:41:40 from the work of three people initially,

00:41:43 I guess.

00:41:44 Very important

00:41:45 in the applications

00:41:46 of perturbation theory

00:41:47 was, in fact,

00:41:49 the work of Foucault.

00:41:50 Foucault not only showed us

00:41:53 that frontier orbitals are important,

00:41:55 but his thinking about them

00:41:57 was consistently in the language

00:41:58 of perturbation theory.

00:42:00 If two orbitals are closer to each other,

00:42:02 they will interact more.

00:42:04 Michael Doerr was also

00:42:05 extremely important

00:42:06 in applying perturbation theory

00:42:09 and the whole English school

00:42:11 of Coulson and Long and Higgins.

00:42:13 And also important to me

00:42:14 was a friend and a colleague,

00:42:16 and that was Lionel Salem,

00:42:18 who was able somehow...

00:42:22 He shared very much

00:42:23 my orientation toward chemistry.

00:42:25 He came from a physical background,

00:42:28 but he liked complexity in molecules,

00:42:31 and he and I have thought

00:42:33 about molecules in similar ways.

00:42:35 And his uses of perturbation theory

00:42:37 influenced my thinking.

00:42:39 Yes, his use was applied

00:42:40 much more to photochemistry

00:42:42 and excited states.

00:42:43 Yes, that's right.

00:42:46 He thought in ways

00:42:48 that were similar to mine.

00:42:50 Now, I think these uses

00:42:51 of perturbation theory

00:42:54 have had an impact

00:42:57 in that they influenced how,

00:43:01 as you said,

00:43:02 in that period, 65 to 69,

00:43:04 how other people thought

00:43:06 about chemistry

00:43:08 and also how they thought

00:43:09 about theory.

00:43:10 That is, it had an influence

00:43:11 on organic chemists, let us say,

00:43:13 and it also had an influence

00:43:14 upon theoretical chemists.

00:43:17 The organic chemists, of course,

00:43:19 were impressed by the applicability

00:43:22 of such simple arguments

00:43:24 to molecular structure

00:43:27 and reactivity.

00:43:28 And it's the reactivity,

00:43:30 especially in such

00:43:31 highly stereospecific reactions

00:43:33 as we were concerned with

00:43:35 in the orbital symmetry rules,

00:43:37 it's this reactivity,

00:43:39 our ability to explain details

00:43:41 of stereochemistry,

00:43:42 which had an impact.

00:43:44 And the initial explanation

00:43:45 was in a language

00:43:46 that organic chemists

00:43:47 could understand.

00:43:49 They knew what the highest orbital

00:43:51 of butadiene was like.

00:43:53 That was part of common knowledge

00:43:54 among a progressive group

00:43:56 of organic chemists in the 60s.

00:43:58 And they could make

00:44:00 the extrapolations that we did,

00:44:02 and we made it for them

00:44:05 in a language,

00:44:07 and this is one of the things

00:44:08 that I learned,

00:44:09 in a language that was accessible

00:44:11 to organic chemists.

00:44:13 It was not obscured

00:44:14 by lots of numbers

00:44:15 and lots of formulas.

00:44:17 So it was a portable explanation.

00:44:19 That, I think, had a tremendous impact.

00:44:22 Now, there was also an impact

00:44:24 on the theorists.

00:44:25 All the time,

00:44:26 calculations were getting better.

00:44:28 People were able,

00:44:29 with larger computers,

00:44:30 to do better and better calculations

00:44:32 on organic molecules,

00:44:34 with larger basis sets,

00:44:35 more accurate calculations.

00:44:37 But I think what happened

00:44:38 was that even those theoreticians

00:44:41 who were working

00:44:42 in a calculating mode

00:44:44 found themselves pressed

00:44:46 by their colleagues

00:44:47 and by the general trend

00:44:49 of the times,

00:44:50 by the success of these explanations

00:44:51 that we had,

00:44:52 to adumbrate explanations

00:44:56 which were simpler.

00:44:58 And I think that's a good thing.

00:44:59 I think that's a good thing, overall.

00:45:01 So I think, actually,

00:45:02 I can perceive an influence

00:45:05 of the simple orbital symmetry ideas

00:45:07 even on the work

00:45:08 of other highly sophisticated theoreticians,

00:45:11 indirectly.

00:45:13 Yes, and during the decade

00:45:15 of the 1970s

00:45:17 and at the present time,

00:45:19 well, during that decade,

00:45:20 this whole way of thinking

00:45:22 about organic chemistry,

00:45:23 this applied perturbation theory,

00:45:25 has become part

00:45:28 of every graduate organic education,

00:45:30 and now it's just a part

00:45:31 of their normal course,

00:45:33 and we see these arguments

00:45:34 in many scientific papers.

00:45:37 But during this period,

00:45:39 you switched

00:45:41 into inorganic chemistry.

00:45:43 Yes, that's right.

00:45:45 I did.

00:45:47 I should say it.

00:45:48 Why?

00:45:49 First of all,

00:45:50 it wasn't that much of a switch

00:45:51 as one might imagine.

00:45:53 Remember that I came,

00:45:54 in some way,

00:45:55 from boron hydrides,

00:45:56 which were inorganic.

00:45:57 It's true what I switched.

00:45:58 I switched,

00:45:59 and I switched

00:46:00 to some main group

00:46:03 molecules involving phosphorus,

00:46:04 and then eventually

00:46:05 transition metal complexes.

00:46:07 A number of reasons for this.

00:46:12 I learned,

00:46:14 I became fascinated

00:46:16 through, I think,

00:46:17 a Baker lecture here,

00:46:19 primarily by Earl Nudities,

00:46:21 in phosphorus

00:46:23 in five coordination,

00:46:24 and in higher coordination

00:46:25 in general.

00:46:26 While he was still at DuPont.

00:46:27 While he was still at DuPont,

00:46:28 before he became my colleague.

00:46:30 And Earl talked about

00:46:32 pentacoordinate phosphorus,

00:46:34 and I got interested.

00:46:35 I had already been somewhat

00:46:36 interested earlier

00:46:37 in that group of molecules,

00:46:42 and that formed a transition

00:46:43 to inorganic molecules.

00:46:46 I had, by 1972 or so,

00:46:51 had a group of talented co-workers

00:46:55 such as Rolf Gleiter,

00:46:57 who went on

00:47:00 and were able to apply

00:47:02 the same methods that I used

00:47:03 to other organic molecules.

00:47:06 And so,

00:47:08 and also the school at Arce

00:47:11 with Salem and Nguyen

00:47:13 and their co-workers

00:47:14 were able to do similar things.

00:47:15 Many people were able

00:47:16 to do these things

00:47:17 once we showed

00:47:18 that it could be done.

00:47:20 I began to feel

00:47:22 a little bit pressed

00:47:24 by having

00:47:28 most of the easily done problems

00:47:31 solved,

00:47:32 and what remained

00:47:33 were difficult problems.

00:47:35 So I guess one motivation

00:47:38 to move on

00:47:39 could be just said

00:47:40 to be laziness.

00:47:41 I'm sorry, it's a bad motivation,

00:47:42 but I didn't want to tackle

00:47:44 some of the harder problems

00:47:45 like salvation,

00:47:46 the influence in solvent

00:47:48 and chemical reactions.

00:47:49 Obviously a force in reactivity,

00:47:51 but that was much more

00:47:53 difficult to do.

00:47:55 The other thing was

00:47:56 I saw the inorganic area

00:47:59 as really open

00:48:01 to the same kinds

00:48:02 of frontier orbital considerations,

00:48:05 to the same types

00:48:06 of little simple

00:48:07 perturbation arguments.

00:48:09 There was one person, perhaps,

00:48:12 who was doing similar thinking,

00:48:14 and that was Leslie Orgel,

00:48:16 and he left the field

00:48:17 for molecular biology

00:48:18 some time before.

00:48:20 There were other people

00:48:21 who were doing calculations,

00:48:24 but they were not thinking

00:48:26 quite in the same way.

00:48:28 And even though I found

00:48:30 inorganic chemists

00:48:31 quite cognizant of symmetry,

00:48:33 remember symmetry is so

00:48:35 deeply involved in

00:48:36 crystal field theory,

00:48:37 which at that time

00:48:38 was a successful model

00:48:39 in inorganic chemistry.

00:48:41 All the inorganic chemists,

00:48:42 I didn't have to teach them

00:48:43 what T2G and EG meant,

00:48:45 whereas I had to teach that

00:48:46 in some way to organic chemists.

00:48:49 But nevertheless,

00:48:50 even though they were

00:48:51 cognizant of symmetry

00:48:52 and used it in a

00:48:53 spectroscopic sense,

00:48:55 they did not really use

00:48:57 frontier orbital arguments

00:48:58 as determinants of structure

00:49:00 and reactivity.

00:49:02 So it was a wide open field,

00:49:05 I felt.

00:49:06 And then as I began reading,

00:49:08 I just got fascinated

00:49:10 by the structural complexity.

00:49:12 Once again, the structure,

00:49:13 the stereochemistry,

00:49:15 drew me in, sucked me in.

00:49:17 It was just beautiful

00:49:19 to learn the literature

00:49:21 of inorganic chemistry

00:49:23 and to have a feeling

00:49:25 of being in touch

00:49:27 with what was being done

00:49:28 and see these complicated

00:49:30 structures of higher

00:49:32 coordination,

00:49:33 of complicated polyhedra,

00:49:37 just geometrically

00:49:38 beautiful structures often.

00:49:40 So I began to work

00:49:42 on inorganic molecules

00:49:43 and I have had

00:49:46 a very talented group

00:49:48 of co-workers over the years

00:49:50 who have helped me

00:49:52 in the last ten years

00:49:53 to make some sense

00:49:55 of the electronic structure

00:49:56 of inorganic molecules.

00:49:58 If one looks at it in detail,

00:50:00 what we've done

00:50:02 uses similar methodology

00:50:04 to what we used

00:50:05 in the organic realm.

00:50:07 So it's not terribly

00:50:09 adventurous from that

00:50:10 point of view.

00:50:12 One of the things I'm

00:50:13 proudest of in the end

00:50:15 is now this isolobal

00:50:17 analogy.

00:50:19 In fact, I used in the

00:50:20 Nobel lecture, I used

00:50:22 instead of talking about

00:50:23 the orbital symmetry,

00:50:24 I talked about some of our

00:50:25 organometallic work.

00:50:26 The isolobal analogy

00:50:27 is a way of seeing

00:50:29 resemblances between

00:50:30 the orbitals of organic

00:50:32 fragments like methyl,

00:50:33 methylene, methine

00:50:35 and inorganic fragments

00:50:37 like a metal with

00:50:38 three, four, five

00:50:40 ligands around it.

00:50:41 That similarity allows

00:50:42 one to see parallels

00:50:44 between organic molecules

00:50:46 and transition metal

00:50:47 complexes so that

00:50:49 cyclobutadiene iron

00:50:51 tricarbonyl, which I just

00:50:52 talked about, in fact

00:50:54 has a very close

00:50:55 resemblance to C5H5+,

00:50:58 an interesting cation

00:51:01 which is unstable but

00:51:03 which may have a

00:51:05 local minimum in a

00:51:06 square pyramidal structure.

00:51:08 And its electronic

00:51:09 structure is very close

00:51:10 to that of cyclobutadiene

00:51:11 iron tricarbonyl.

00:51:13 It's been lots of fun

00:51:14 in the inorganic realm.

00:51:16 And now, of course,

00:51:17 these arguments also

00:51:18 are being applied by

00:51:19 others.

00:51:20 Yes, they are.

00:51:23 I think they have

00:51:24 penetrated the inorganic

00:51:27 realm and are used

00:51:30 consistently by

00:51:32 modern organometallic

00:51:33 chemists.

00:51:35 Maybe it's time to

00:51:36 leave again.

00:51:37 Well, if you leave

00:51:39 that field, what next?

00:51:40 Biochemistry?

00:51:42 No, I don't think so.

00:51:46 I think the next field

00:51:50 where I think one

00:51:53 could make a

00:51:56 contribution is the

00:51:57 field of solid state

00:51:59 chemistry and physics.

00:52:02 And there are several

00:52:03 reasons for that.

00:52:05 Once again, the field

00:52:06 is wide open.

00:52:11 There is one person

00:52:13 with whom I have had a

00:52:15 small association.

00:52:16 That's Jeremy Burdett,

00:52:17 who is making new ideas

00:52:21 in that field.

00:52:22 But by and large, in the

00:52:23 field of solid state

00:52:24 chemistry, and again I'm

00:52:25 thinking of the

00:52:26 determinants of structure

00:52:27 and reactivity.

00:52:28 Why do complicated

00:52:30 mineral or alloy

00:52:31 structures have the

00:52:32 structures that they do?

00:52:36 And I'm thinking of

00:52:37 reactivity of solids and

00:52:38 surfaces as well.

00:52:41 By and large, ideas of

00:52:42 packing and Coulomb

00:52:45 forces have dominated

00:52:47 our ideas about these

00:52:49 things.

00:52:50 And whereas they are

00:52:51 probably applicable to

00:52:53 the more highly ionic of

00:52:55 these, nevertheless I

00:52:57 think of many of these

00:52:58 things, with the

00:52:59 exception of simple

00:53:00 ionic crystals, as being

00:53:02 complicated molecules

00:53:04 often with covalent

00:53:05 forces rather than

00:53:07 ionic, or at least some

00:53:08 continuum between

00:53:09 covalent and ionic.

00:53:11 And I think the field

00:53:12 has been generally

00:53:14 open.

00:53:15 There is a great deal to

00:53:17 do.

00:53:18 There is complexity in

00:53:19 the field.

00:53:20 I told you I like

00:53:21 complexity.

00:53:22 I think people who look

00:53:23 at solid state

00:53:24 structures, people who

00:53:27 look at solid state

00:53:28 structures think that

00:53:32 they are in fact very

00:53:33 complicated.

00:53:34 And I think they

00:53:35 probably are.

00:53:36 But one can learn to do

00:53:37 it.

00:53:38 The other thing is I

00:53:39 think actually there is

00:53:40 something that from a

00:53:42 chemical perspective we

00:53:43 can teach the physicists

00:53:45 here.

00:53:46 And I have always viewed

00:53:49 my role very strongly as

00:53:51 an educational one.

00:53:55 I see very little

00:53:57 separation between

00:53:58 teaching and research.

00:53:59 I think the reason I'm,

00:54:01 if I'm any good in my

00:54:03 research, it's because

00:54:06 I've learned how to

00:54:08 explain things in

00:54:09 freshman chemistry.

00:54:10 I'm just explaining it to

00:54:11 a different audience.

00:54:12 The audience is some

00:54:13 people out in the world.

00:54:14 I don't take very

00:54:15 different attitudes about

00:54:16 that process.

00:54:17 I think it's a teaching

00:54:18 process.

00:54:19 And if you look carefully

00:54:20 at our papers, the large

00:54:21 concentration of

00:54:22 drawings, of graphic

00:54:23 material in them, all

00:54:25 those orbital drawings,

00:54:26 and the occasional

00:54:29 unwillingness to

00:54:30 contract but rather to

00:54:31 repeat arguments are part

00:54:33 of a strategy of

00:54:35 pedagogical

00:54:36 effectiveness.

00:54:37 It gets me into trouble

00:54:38 sometimes.

00:54:39 I was going to ask, does

00:54:40 this get you into

00:54:41 problems with referees?

00:54:42 Yes, it does.

00:54:43 But to get back to

00:54:44 solid state chemistry and

00:54:45 physics, I think the

00:54:47 physicists can do

00:54:48 calculations on solids,

00:54:51 band calculations of the

00:54:52 electronic structure

00:54:53 solids.

00:54:54 I don't think they

00:54:55 really understand them in

00:54:57 a chemical sense.

00:54:58 What I mean by that is

00:54:59 that they don't

00:55:01 decompose them into

00:55:02 pieces.

00:55:03 They don't look at the

00:55:04 reasons why a molecule

00:55:06 has a certain structure

00:55:07 rather than an

00:55:08 alternative one.

00:55:10 And I think those

00:55:11 reasons ultimately are

00:55:13 to be found in simple

00:55:15 frontier orbital

00:55:16 thinking, in the

00:55:17 electronic structure of

00:55:18 the solid.

00:55:19 I mean, what else is in

00:55:20 there?

00:55:21 It's the same orbitals,

00:55:22 it's just in a more

00:55:23 complicated setting.

00:55:24 We have to get used to

00:55:26 a thinking about these

00:55:30 extended structures and

00:55:32 about translational

00:55:33 symmetry.

00:55:34 And this is where I

00:55:35 think I can play an

00:55:36 educational role to the

00:55:37 chemist.

00:55:38 I think I can

00:55:39 translate, I can

00:55:40 convince, well, my

00:55:43 conviction has always

00:55:44 been if I can learn

00:55:45 something, I can teach

00:55:46 somebody else to do

00:55:47 this.

00:55:48 And if I understand

00:55:49 what a Brillouin

00:55:50 zone and a Fermi

00:55:51 level and the density

00:55:52 of states is, I think I

00:55:54 can teach people to do

00:55:55 it.

00:55:56 And so I would like

00:55:58 to do something about

00:56:01 solid state chemistry.

00:56:04 Well, I wish you a

00:56:06 great deal of success

00:56:07 in this.

00:56:08 I'm sure you will have

00:56:09 success and will have

00:56:10 the same kind of impact

00:56:12 in that area of

00:56:13 chemistry that you've

00:56:14 had on orbital symmetry

00:56:16 applied to organic

00:56:17 chemistry and applied to

00:56:19 inorganic chemistry as

00:56:20 well.

00:56:21 Thank you.