"I love seeing connections," says chemist, poet and Nobel laureate Roald Hoffmann of Cornell University. "I can teach chemists the language of solid-state physics, and maybe teach physicists the inherent value of chemical bonding concepts."

very chemist is familiar with the Woodward-Hoffmann rules that predict the products of reactions in organic chemistry. The theory was the result of collaborations between Robert Burns Woodward (1917-1979), the organic chemist, and Roald Hoffmann, the theoretical chemist. Both went on to win Nobel prizes–Woodward in 1965, for his work with natural products, and then Hoffmann in 1981, his prize specifically recognizing the importance of his theory in explaining organic chemistry by the behavior of electrons and the molecular orbitals in which they move. In his time, Hoffmann has published in many areas, as is demonstrated in the listing of his most-cited papers.

   Roald Hoffmann is also a literate chemist, as we can see from his recent book Chemistry Imagined: Reflections on Science. This is a joint publication with the artist Vivian Torrence, and combines essays, poems, and articles with a series of collages inspired by chemistry. Torrence has been a visiting scholar at Cornell University in Ithaca, New York, where Hoffmann is Professor of Physical Science, and her work has been exhibited in art galleries across the United States. Hoffmann's literary achievement shows that chemistry can be a worthwhile, if unexpected, subject for poetry and prose.

   Hoffmann was born in eastern Poland in 1937, just before that part of his native country was occupied by the Soviet Union in 1939. In 1941 it was overrun by the Nazis, and although he was of Jewish parents, Hoffmann survived the Second World War. He emigrated to the U.S. in 1949, settled in New York, and went to Stuyvesant High School. From there he went to Columbia College and graduated in 1958. His next stop was Harvard, where he was awarded an M.A. in physics in 1960 and a Ph.D. in chemical physics in 1962, working under the supervision of Martin Gouterman and William Lipscomb. His research involved applying the theory of molecular orbitals to polyhedral collections of atoms.

   Hoffmann continued at Harvard as a Junior Fellow. He met his wife Eva at a summer school in Sweden, and they eventually had two children, Hillel and Ingrid. Meanwhile he began his collaboration with Woodward, and together they developed the theory that now bears their names. This was written up in five benchmark papers that were published in 1965 while Hoffmann was still only 28. Their impact was immediate and they quickly became a part of every organic chemist's vocabulary. Hoffmann then moved to Cornell to his first teaching post and was promoted to professor in 1968.

   In 1972 Hoffmann was elected to the National Academy of Science and two years later became the John A. Newman Professor of Physical Science at Cornell. In 1981 Hoffmann won the Nobel Prize for chemistry, which he shared with Kenichi Fukui. The following year the American Chemical Society gave him their Inorganic Chemistry award, attesting to the span of Hoffmann's influence–by this time he was transforming the theory that underpins this area of the subject, just as he had once transformed organic chemistry.

From his office at Cornell,
Hoffmann spoke with chemistry correspondent John Emsley.

During your life you have researched all branches of chemistry. What are you working on at the moment?

   Hoffmann: Right now I'm intent on understanding how molecules that go on almost infinitely in one, two, or three dimensions are held together–in other words, polymers, surfaces, and solids. I think what I can contribute is an understanding of the relationship of this kind of bonding to that in small molecules. I love seeing connections! And I can teach chemists the language of solid-state physics, necessary for this field, and maybe (but much harder) I can teach physicists the inherent value of chemical bonding concepts.

or many chemists, a Nobel Prize comes as the culmination and international recognition of a lifetime's work. Thereafter the recipient could be forgiven for merely keeping the same research pot simmering gently. A look at Hoffmann's work since 1981 shows that he continues to work at full heat, producing highly rated papers that attract multiple citations. The table lists his personal Hot Ten for the years subsequent to his Nobel Prize of 1981. These were taken from ISI's database and reveal that a 1982 article in Angewandte Chemie is #1 with an incredible 701 citations (an average of 50 per year). This is perhaps not unexpected because it is an account of his Nobel Lecture. Below this we find papers with more than 10 citations per year, mainly in the areas of inorganic and solid-state chemistry, where Hoffmann has applied his skills to investigating the structure, bonding, and behavior of organic molecules towards metals. This kind of information is essential if we are to understand the chemical behavior of systems as diverse as enzymes and industrial catalysts. Yet while many chemists labor in this particular vineyard, few pick the bumper harvest that Hoffmann gathers. Of the ten papers, all but one have collected over 100 citations, a remarkable achievement for any chemistry paper. Roald Hoffmann's Highest Impact Papers Published Since 1981 (Ranked by average citations per year, with citations updated through 1996) Rank Paper Citations through 12/93* Citations through 12/96 Avg. cites per year through 1996 1 R. Hoffmann, "Building bridges between inorganic and organic chemistry: Nobel lecture," Angew. Chem., 21(10):711-24, 1982. 581 701 50 2 J.Y. Saillard, R. Hoffmann, "C-H and H-H activation in transition metal complexes and on surfaces," J. Amer. Chem. Soc., 106(7):2006-26, 1984. 397 487 37 3 R. Hoffmann, "A chemical and theoretical way to look at bonding on surfaces," Rev. Mod. Phys., 60(3):601-28, 1988. 78 148 19 4 D.M. Hoffman, R. Hoffmann, C.R. Fisel, "Perpendicular and parallel acetylene complexes," J. Amer. Chem. Soc., 104(14):3858-75, 1982. 192 241 16 5 K. Tatsumi, R. Hoffmann, A. Yamamoto, J.K. Stille, "Reductive elimination of D8-organotransition metal complexes," Bull. Chem. Soc. Japan, 54(6):1857-67, 1981. 178 217 14 6 O. Eisenstein, R. Hoffmann, "Transition metal complexed olefins: How their reactivity towards a nucleophile relates to their electronic structure," J. Amer. Chem. Soc., 103(15):4308-20, 1981. 178 202 13 7 C. Janiak, R. Hoffmann, "Tl(I)-Tl(I) and in(I)-in(I) interactions: From the molecular to the solid state," J. Amer. Chem. Soc., 112(16):5924-46, 1990. 54 70 12 8 S. Alvarez, R. Vicente, R. Hoffmann, "Dimerization and stacking in transition metal bisdithiolenes and tetrathiolates," J. Amer. Chem. Soc., 107(22):6253-77, 1985. 106 133 12 9 P. Kubacek, R. Hoffmann, Z. Havlas, "Piano stool complexes of the CPML4 type," Organometal., 1(1):180-8, 1982. 149 176 12 10 S.S. Sung, R. Hoffmann, "How carbon monoxide bonds to metal surfaces," J. Amer. Chem. Soc., 107(3):578-84, 1985. 112 137 11 SOURCE: ISI's Personal Citation Report, 1981-1996 * citations reported with original interview

Do you think our two sciences are moving back to sharing more common ground again?

   Hoffmann: Definitely. Look at some of the exciting areas in physics: high-temperature superconductors, quasicrystals, fullerenes, organic ferromagnets, surface science–they're full of questions that chemists would call structure and reactivity. It's wonderful–all those physicists who avoided chemistry at university now having to learn some!

Your current interest is in large molecular structures like the ones you have just mentioned, but what other parts of chemistry should we be looking at? If you were in charge of a major budget for funding chemistry research, what areas would you give grants to?

   Hoffmann: I am not sure I would want to be in such a position... but knowing for sure that the best works would be different from what I would invest in, I would support the following areas: (1) ways to achieve control in synthesis in two and three dimensions, by which I mean the making of thermodynamically unstable, but persistent molecules; (2) environmentally more benign syntheses; (3) solid-state compounds of carbon and metals, so-called metal carbides; and (4) surface chemistry of water.

Some of these clearly would be of commercial interest, and that brings me to another point. Industrialists complain that too few young people today want to study chemistry. What can we do about it?

   Hoffmann: I disagree that we need more chemists. Where are the jobs for them? Are the salaries for chemists rising? I actually think we are in a situation of a decent balance between supply and demand of highly trained personnel in chemistry. Some people claim that if we had more research it would generate more jobs for scientists, but that sort of exponential growth can't go on. You also need intelligent merchants, nurses, city councillors, teachers, garbage collectors, etc.

But what about them being intelligently trained to understand chemistry? Surely we need more people in society who can understand chemistry issues.

   Hoffmann: I agree that we need a general public that is knowledgeable about chemistry so that people in the various approximations of democracy that the world aspires to can make intelligent decisions, unseduced by "experts" who can be found for any side on an issue. In particular I am thinking of issues with a chemical content, such as the control over automobile emissions, the placement of chemical plants, the directions of research, the use of animals and people, etc. Without such knowledge, the brilliant young chemists–these seekers after deep molecular knowledge, the transformers of matter of the future–will never be able to work at their potential. For it is society, made up of nonchemists, that supports what chemists do, and I think this is right. But I want people to understand what we do, at least enough not to be afraid of our science.

Let me turn to the side of your life that particularly interests me: Hoffmann the writer and poet. In your book Chemistry Imagined you have a poem called "Giving In" that is about xenon gas becoming metallic at 1.4 million atmospheres. In it you successfully capture the emotion of very high pressure with powerful analogies of torture in Argentina and the death of a deep-sea diver. Chemistry and poetry seem worlds apart, yet you manage to combine the two. What's your secret?

   Hoffmann: I believe the secret is twofold: firstly, I love the English language and its hidden, associative ways; and secondly, I try–and I am not afraid of exposing my failures in trying to write. Poetry and chemistry have like value, for they are both deep, human ways to understand the same and not the same, to live in this beautiful and terrible world.

Finally, and perhaps the hardest question of all: if you had to choose between a career as a scientist or artist, which would you choose?

   Hoffmann: As I finished my undergraduate career at Columbia I was caught between the wonders of chemistry and the sweet seduction of the humanities, especially art history. I decided–an existential act–for chemistry. And I've had a wonderful time, wending my way, trying to understand and connect all of chemistry, and teaching what I've learned. If I had to choose, I'd choose chemistry again. For I know that I can do both science and art (at least writing), art in science, science in art. But I'd have a harder time doing chemistry if I were primarily a writer or artist. And besides, society, for the wrong reasons, pays chemists better.

Dr. John Emsley, FRSC, is Science Writer in Residence at the Department of Chemistry, Imperial College, London, U.K.