Chemical Education Today
Nobel Centennial Essays
A Century of Chemical Dynamics Traced through the Nobel Prizes
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1981: Fukui and Hoffmann by J. Van Houten
Nobel Prize in Chemistry 1981 Kenichi Fukui (1918–1998) Roald Hoffmann (1937– )
for their theories, developed independently, concerning the course of chemical reactions This is the seventh in a series of essays written in commemoration of the centennial of the Nobel Prize, examining the history of chemical dynamics in the 20th century. During the first eight decades of the 20th century only six Nobel Prizes (1) were awarded for work related to chemical dynamics. Those first six prizes could be divided chronologically into two groups—three in the first decade of the century focus on developments that are fundamental to our understanding of the rates and mechanisms of chemical reactions (1 a–c), and three in the middle decades of the century for work on isotope tracers (1d), on chain reaction mechanisms (1e), and on methods of monitoring reactions in the sub-millisecond time regime (1f ). The 1981 Nobel Prize awarded to Kenichi Fukui and Roald Hoffmann represents the first of three Prizes for work in chemical dynamics during the decade of the 1980s. Unlike all the previous awards in chemical dynamics, the 1981 award recognized work that was more theoretical and that allowed chemists to predict in advance the course and the ultimate products of certain reactions. As their official Nobel citation (2 ) states, the 1981 Laureates developed theories independently that led to what has come to be known collectively as the theory of conservation of orbital symmetry. Fukui, working in Japan, developed “frontier orbital theory” beginning in 1952. Hoffmann, working initially with Robert Burns Woodward at Harvard in 1964, developed a principle of conservation of orbital symmetry in chemical reactions that was first described in a series of communications (3) appearing in the Journal of the American Chemical Society in 1965. The correlation diagrams that are often associated with the so-called “Woodward–Hoffmann rules” appeared in 1965 in backto-back papers in JACS authored by H. C. Longuet-Higgins and E. W. Abrahamson (4) and by Hoffmann and Woodward (3b). The name “Woodward–Hoffmann rules” has led some to the misconception that Woodward and Hoffmann shared a Nobel Prize. Woodward did win a Nobel Prize in 1965 for “outstanding achievements in the art of organic synthesis” (5), but his untimely death in 1979 made him ineligible for a second Prize in 1981. Hoffmann has observed that all the award nominations prior to Woodward’s death were for the two of them together. He is certain (6) that had Woodward
lived, he would have won a share of the 1981 Prize, thereby becoming only the second person to win two chemistry Nobel Prizes.1 The 1981 Nobel citation (2) notes that “a characteristic feature of Fukui’s and Hoffmann’s method of attacking difficult and complicated problems is that they succeeded in making generalizations through simplifications.” The citation goes on to say that the “theories are milestones in the development of our understanding the course of chemical reactions” and that they “provide guidance for experimental researchers and save them time.” The idea of orbital symmetry as a diagnostic tool for reaction pathways has today become a mainstay in the teaching of mechanistic organic chemistry. Of course, Fukui’s frontier orbitals, and the Woodward–Hoffmann rules are not limited to organic reactions, and chemists in a variety of sub-disciplines utilize them. In 1970 Woodward and Hoffmann published their book, The Conservation of Orbital Symmetry, (7 ) which was, in fact, an unchanged reprint of a long article they had published in Angewante Chemie (6, 8 ) the previous year. Fukui summarized his work in an article in Accounts of Chemical Research (9 ) the next year. A book edited by Fukui and Hiroshi Fujimoto (10), published shortly before Fukui’s death, discusses the basic concepts of his theory and describes up-to-date applications. The Woodward– Hoffmann rules have been discussed a number of times in the pages of this Journal—as early as 1968 and 1970 with two articles by Vollmer and Servis (11 , 12), and as recently as 1999 with back-to-back articles by David and Patterson (13, 14 ). An article in this Journal by R. F. Langler in 1996 (15 ) compared and contrasted Fukui’s frontier orbital approach and Woodward and Hoffmann’s correlation diagrams with a third approach proposed by Zimmerman and Dewar (16). Kenichi Fukui was the first—and until the awards in 2000 and 2001 to Hideki Shirakawa and Ryoji Noyori (17), the only—Japanese chemist to win a Nobel Prize. Fukui graduated from Kyoto Imperial University in 1941 and was engaged in research on synthetic fuels for the Japanese Army during World War II. He became a lecturer in Fuel Chemistry at Kyoto Imperial University in 1943, received his Ph.D. in engineering in 1948 and was named professor in 1951 (2, 18, 19). In his Nobel autobiography (2) Fukui stated that his “first scientific delight came in 1952 when [he] found a correlation between the frontier electron density and the chemical reactivity in aromatic hydrocarbons.” He went on to comment that his 1952 paper was published in the same year as the important paper on the
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charge transfer force in donor-acceptor complexes by Robert Mulliken, who won the 1966 chemistry Nobel Prize for developing the molecular orbital method that is named for him (20), and that the influence of Mulliken’s paper provided the theoretical foundation to Fukui’s “consideration of the importance of electron delocalization between the frontier orbitals of reactant species.” Fukui published 137 papers in Japanese on experimental organic chemistry and reaction engineering and on catalytic engineering between 1944 and 1972, but he stated (2) that his main work in chemistry was best “represented by more than 280 English publications, of which roughly 200 concern the theory of chemical reaction and related subjects.” Nevertheless, his JCE Online biography (18) notes that “the first publication of his theoretical work on the relationship between molecular orbitals and chemical reactivity in 1954 was largely ignored because many experimental chemists at that time did not have the necessary mathematical background to understand its potential; also, many theoretical chemists thought the theory too simplistic.” In addition to his accomplishments as an experimentalist and a theoretician, Fukui was recognized for his efforts to promote science education in Japan (19). In May 1988 the Ministry of Education, Science and Culture of Japan opened the Institute for Fundamental Chemistry in Kyoto, with Fukui as its first director (21). Roald Hoffmann is the second Polish emigrè to receive the chemistry Nobel Prize—the first was Marie Sklodowska Curie (22). He was born in 1937 in Zloczow. (The town was part of Austria–Hungary when his parents, Hillel Safran and Clara Rosen, were born, was in Poland at the time of his birth, became part of the Soviet Union after World War II, and is now part of the Ukraine.) In his Nobel autobiography (2), Hoffmann provides many intimate details of his experiences as a young member of a Jewish family in Nazi-occupied Poland and his later education in the United States. The 668
photo: Clemens A. Loew
Nobel Centennial Essays
Roald Hoffmann (above) and Kenichi Fukui (right)
Nazis executed his father in 1943; afterwards his mother married Paul Hoffmann, a Polish Jew who had survived the Holocaust (6). The family came to the United States in 1949 where Hoffmann learned English as his sixth language while attending public schools in Brooklyn and at New York’s Stuyvesant High School. He did his undergraduate work at Columbia and his graduate work at Harvard, receiving his Ph.D. in 1962. After completing his doctorate, Hoffmann remained at Harvard as a Junior Fellow working with R. B. Woodward investigating electrocyclic reactions. They were seeking an explanation of the mechanistic details of one reaction in the complicated sequence by which Woodward and Albert Eschenmoser and co-workers were attempting to synthesize vitamin B (2, 3, 6, 23 ). Woodward and Hoffmann shared the American Chemical Society’s A. C. Cope Award in Organic Chemistry in 1973. Hoffmann also received the ACS Award in Pure Chemistry in 1969, the ACS Award in Inorganic Chemistry in 1982, the Priestley Medal in 1990, the National Medal of Science in 1983, and the ACS George C. Pimentel Award in Chemical Education in 1996. He has also been recognized by his native Poland and is a prominent member of
the Polish Institute of Arts and Sciences in America (23). In 1965 Hoffmann joined the faculty at Cornell University where he remains. He is the John A. Newman Professor of Physical Science, but like the 1956 Nobel Laureate, Cyril Hinshelwood (1e), he is also a man of letters: he is the Frank H. T. Rhodes Professor of Humane Letters at Cornell and is a Fellow of the American Philosophical Society and the American Academy of Arts and Sciences (24). He has published a number of volumes of poetry; three popular-science books (25, 26, 27); and numerous articles in American Scientist. He participated in the production of a series of 26 halfhour television episodes entitled “The World of Chemistry” that aired on PBS in 1990. He is co-author of the play, Oxygen, which describes a plan to present “retro-Nobel Prizes” to the discoverers of oxygen on the occasion of the Nobel Prize centennial (28). In his 1996 Pimentel Award lecture entitled “Teach to Search” (29), Hoffmann spoke in detail about the important connections between research and teaching. He observed that the primary requisite for being a good teacher—the ability to communicate difficult material to a variety of audiences—is the same as that required to become a world-class researcher.
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The 1981 Nobel citation (2) for Fukui and Hoffmann concludes: “Good theoretical models provide guidance for experimental researchers and save them time. Fukui’s and Hoffmann’s theories are milestones in the development of our understanding of the course of chemical reactions. This development has, however, by no means been brought to a halt by the prizewinning work. This work has provided inspiration for new lines of development. Fukui and Hoffmann are among the most active researchers in these areas.” Except for the fact of Fukui’s death in 1998, those words would remain true today. Also remaining true are the concluding sentences of Woodward and Hoffmann’s seminal text, The Conservation of Orbital Symmetry (7, 8): “Since every elementary step in any chemical reaction is a concerted process, correlative ideas must be applicable to all reactions. … [O]nly the imagination sets limits upon the number and variety of new and fascinating molecules which may be designed to favor reactions as yet undiscovered, but now known to be feasible.” W
Supplemental Material
A list of all recipients of the Nobel Prize in Chemistry, their affiliations, and the work for which the award was made, is available in this issue of JCE Online. Note 1. The only double chemistry Laureate is Frederick Sanger, in 1958 and 1980. Some readers may recall that Linus Pauling and Marie Curie each won two Nobel Prizes. Pauling’s 1954 Prize was in chemistry, however his 1962 award was the Peace Prize. Curie shared the 1903 physics Prize with her husband, Pierre, and with Henri Becquerel; she was the sole recipient of the 1911 chemistry Prize. See the Nobel e-Museum at http://www.nobel.se for more information.
Literature Cited 1. a. Van Houten, J. J. Chem. Educ. 2001, 78, 1572–1573; b. ibid, 2002, 79, 21–22; c. ibid, 2002, 79, 146–148; d. ibid, 2002, 79, 301–304; e. ibid, 2002, 79, 414–416; f. ibid, 2002, 79, 548–550. 2. Nobel e-Museum–Chemistry 1981 (with links to Prize Presentation and Biography pages). http://www.nobel.se/chemistry/ laureates/1981/index.html (accessed Feb 2002). 3. a. Woodward, R. B.; Hoffmann, R. J. Am. Chem. Soc. 1965, 87, 395–397; b. Hoffmann, R.; Woodward, R. B. ibid, 1965, 87, 2046–2048; c. Hoffmann, R.; Woodward, R. B. ibid, 1965, 87, 4389–4390. 4. Longuet-Higgins, H. C.; Abrahamson, E. W. J. Am. Chem. Soc. 1965, 87, 2045–2046. 5. Nobel e-Museum–Chemistry 1965 (with links to Prize Presentation and Biography pages). http://www.nobel.se/chemistry/ laureates/1965/index.html (accessed Feb 2002).
6. Hoffmann, R. personal communication. 7. Woodward, R. B.; Hoffmann, R. The Conservation of Orbital Symmetry; Verlag-Chemie: Weinheim, 1970. 8. Woodward, R. B.; Hoffmann, R. Angew. Chemie (Int. Engl. Ed.) 1969, 8, 781–853. 9. Fukui, K. Acc. Chem. Res. 1971, 4, 57. 10. Fukui, K.; Fujimoto, H. Frontier Orbitals and Reaction Paths, Selected Papers of Kenichi Fukui, World Scientific Series in the 20th Century, Vol. 7, World Scientific Publ.: London, 1996. 11. Vollmer, J. J.; Servis, K. L. J. Chem. Educ. 1968, 45, 214– 220; Errata, p 790. 12. Vollmer, J. J.; Servis, K. L. J. Chem. Educ. 1970, 47, 491. 13. David, C. W. J. Chem. Educ. 1999, 76, 999–100; and references therein to ibid, 1982, 59, 288 and ibid, 1991, 68, 129. 14. Patterson, R. T. J. Chem. Educ. 1999, 76, 1002–1007. 15. Langler, R. F. J. Chem. Educ. 1996, 73, 899–903. 16. a. Dewar, M. J. S. Angew. Chemie (Int. Engl. Ed.) 1971, 10, 761; b. Zimmerman, H. E. Accts. Chem. Res. 1971, 4, 272; c. Zimmerman, H. E. Tetrahedron, 1982, 38, 753. 17. Nobel e-Museum–Chemistry 2000, 2001. http://www.nobel.se (accessed Feb 2002). 18. JCE Online Biographical Snapshots–Kenichi Fukui. http:// jchemed.chem.wisc.edu/JCEWWW/Features/eChemists/Bios/ Fukui.html (accessed Feb 2002). 19. Columbia Electronic Encyclopedia–Fukui entry. http:// www.encyclopedia.com/articlesnew/17835.html (accessed Feb 2002). 20. Nobel e-Museum–Chemistry 1966. http://www.nobel.se/chemistry/laureates/1966/index.html (accessed Feb 2002). 21. Institute for Fundamental Chemistry press release. http:// www.ifc.or.jp/seturitu/ifc-e.html (accessed Feb 2002). 22. Nobel e-Museum–Physics 1903, Chemistry 1911. http:// www.nobel.se (accessed Feb 2002). 23. Science in Poland–Roald Hoffmann. http://hum.amu.edu.pl/ ~zbzw/ph/sci/rh.htm (accessed Feb 2002). 24. Hoffmann, R. Autobiography, Cornell University. http:// www.chem.cornell.edu/department/Faculty/Hoffmann/ hoffmann.html (accessed Feb 2002). 25. Hoffmann, R.; Torrence, V. Chemistry Imagined: Reflections on Science; Smithsonian Institution Press: Washington, DC, 1993. 26. Hoffmann, R. The Same and Not the Same; Columbia University Press: New York, 1997. 27. Hoffmann, R.; Schmidt, S. L. Old Wine, New Flasks: Reflections On Science and Jewish Religious Tradition; Freeman: New York, 1997 28. Djerassi, C.; Hoffmann, R. Oxygen; Wiley–VCH: New York, 2001. 29. Hoffmann, R. J. Chem. Educ. 1996, 73, A202–A209.
J. Van Houten is a member of the Department of Chemistry, Saint Michael’s College, Colchester, VT 05439;
[email protected].
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