Kenichi Fukui Nobel Lecture
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- Chemistry 1981
- A191, 39; A192
- K. Fukui
K Fukui 21 Fig. 5. A comparison of HOMO and the interaction frontier orbital for protonation in styrene. FRONTIER ORBITALS IN RELATED FIELDS Theoretical treatments of the property of solid crystals, or chemisorption on a solid surface, appear to have hitherto been almost monopolistically treated by the methodology of physics. But the orbital pattern technique has also ad- vanced gradually in this field. The “cluster approach, ” 81, 82 in which a portion of the metal crystal is drawn out as the form of a cluster of atoms and its catalytic actions or other properties are investigated, has contributed to the development of the orbital pattern approach, because the physical methods mentioned above can hardly be applied to such sizable systems. It is expected that, if clusters of various sizes and various shapes are studied to look into the characteristic feature of their HOMO’s (high-lying occupied MO’s) and LUMO’s (low-lying unoccupied MO’s), the nature of chemisorption and catalytic action, the mode of surface chemical reaction, and several related subjects of interest can be investigated theoretically. As is the case of molecular interactions in usual chemical reactions, only the HOMO- and LUMO-bands lying in the range of several electron volts near the Fermi level can participate in the adsorption of molecules and surface reactions on solid crystals. You may recollect here that, in the BCS (Bardeen-Cooper- Schrieffer) theory of superconductivity, too, only the HOMO’s and LUMO’s in close proximity to the Fermi surface can be concerned in forming electron pairs as the result of interaction with lattice vibration. In the case of solid catalysts mentioned above, the discrimination of particular orbitals and elec- trons from the others have made the situation much easier. Consider a system composed of a regular repetition of a molecular unit, for instance, a one-dimensional high polymer chain or a one-dimensional lattice, in which a certain perturbation is imposed at a definite location. Sometimes it is convenient to discuss the influence of this perturbation by transforming the 22 Chemistry 1981 orbitals belonging to the HOMO-band to construct the orbitals localized at that place. One such technique was proposed by Tanaka, Yamabe and my- self.
83 This method is expected to be in principle applied to a local discussion of such problems as the adsorption of a molecule on the two-dimensional surface of catalysts, surface reactions, and related matters. This approach may be called a little more chemical than the method using the function of local density of states 84 or similar ones, in that the former can be used for the argument of the reactivity of molecules on a catalyst surface in terms of the phase relationship of localized orbitals. What is called low-dimensional semiconductors and some superconductors have also been the objects of application of the orbital argument. In these studies, the dimerization of S 2 N 2 to S
4 N 4 85 and the high-polymerization to ( S N ) x
were discussed, and the energy band structure of (SN) x polymer chain was analyzed to investigate the stable nuclear arrangement and the mode of inter-chain interactions. 87 The modern technique employed in solid state physics to interpret the interesting characteristic behaviours of noncrystalline materials, in particular of amorphous materials, in which the nuclear arrangements were not regular, was certainly striking. Anderson showed generally that in a system of random lattice the electron localization should take place. 56 Mott, stating in his 1977 Nobel lecture that he thought is the first prize awarded for the study of amorphous materials, answered the question, “How can a localized electron be conducted?” with the use of the idea of hopping. Here, too, the HOMO- LUMO interaction - in this case the consideration of spin is essential - would play an important part. Here in a few words, I want to refer to the meaning and the role of virtual orbitals. The LUMO, which has been one of the stars in orbital arguments hitherto discussed, is the virtual orbital which an external electron is consid- ered to occupy to be captured by a molecule to form an anion. Virtual orbitals always play an essential part in producing metastable states of molecules by electron capture. 88
To discuss such problems generally, Tachibana et al. 89 systematized the theory of resonant states from the standpoint of complex eigenvalue problem. The idea of resonant states will take a principal part in chemical reactions, particularly in high-energy reactions which will be devel- oped more in the future. PROSPECT
In introducing above a series of recent results of the studies carried out mainly by our group, I have ventured to make those things the object of my talk which are no more than my prospective insight and are not yet completely estab- lished. This is just to stimulate, by specifying what are the fields I believe promising in the future, the intentional efforts of many younger chemists in order to develop them further. In my opinion, quantum mechanics has two different ways of making partici- pations in chemistry. One is the contribution to the nonempirical comprehen- K. Fukui 23 sion of empirical chemical results just mentioned. However, we should not overlook another important aspect of quantum mechanics in chemistry. That is the promotion of empirical chemistry from the theoretical side. But, also for this second purpose, as a matter of course, reliable theoretical foundations and computational methods are required. The conclusions of theories should be little affected by the degree of sophistication in approximations adopted. On the other hand, for theoreticians to make the second contribution, the cases where predictions surpassing the experimental accuracy are possible by very accurate calculations are for the present limited to those of a very few, extremely simple molecules. In order to accomplish this object in regard to ordinary chemical problems, it becomes sometimes necessary to provide quali- tative theories which can be used even by experimental chemists. If one can contribute nothing to chemistry without carrying out accurate calculations with respect to each problem, one can not be said to be making the most of quantum mechanics for the development of chemistry. It is certainly best that the underlying concepts are as close to experience as possible, but the sphere of chemical experience is steadily expanding. Quantum chemistry has then to perform its duty by furnishing those concepts with the theoretical basis in order to make them chemically available and serviceable for the aim of promoting empirical chemistry. Even the same atoms of the same element, when they exist in different molecules, exhibit different behaviours. The chemical symbol H even seems to signify atoms of a completely different nature. In chemistry, this terrible individuality should never be avoided by “averaging,” and, moreover, innu- merable combinations of such atoms form the subject of chemical research, where it is not the “whole assembly of compounds of different kinds but each individual kind of compounds” that is of chemical interest. On account of this formidable complexity, chemistry possesses inevitably one aspect of depending on the analogy through experience. This is in a sense said to be the fate alloted to chemistry, and the source of a great difference in character from physics. Quantum chemistry, too, so far as it is chemistry, is required to be useful in promoting empirical chemistry as mentioned before. ACKNOWLEDGEMENTS Lastly, I want to mention at this opportunity out of a sense of gratefulness the names of many people in our group who have been walking on the same road as mine since my first paper (1952) on quantum chemistry, particularly Drs. T. Yonezawa, C. Nagata, H. Kato, A. Imamura, K. Morokuma, T. Yamabe and H. Fujimoto, and also I can not forget the names of younger doctors mentioned in the text who made a contribution in opening new circumstances in each field. Among them, Prof. T. Yonezawa was helpful in performing calculations in our 1952 paper, and also, it is to be mentioned with appreciation that the attractive title “frontier orbitals” of my lecture originated from the terminology I adopted in that paper by the suggestion of Prof. H. Shingu, who kindly participated in that paper as an organic chemist to classify the relevant experi-
24 Chemistry 1981 mental results. Furthermore, many other collaborators are now distinguishing themselves in other important fields of chemistry, which, however, have not been the object of the present lecture. It was the late Prof. Yoshio Tanaka of the University of Tokyo and Prof. Masao Horio of Kyoto University who recognized the existence and signifi- cance of my early work in advance to others. I owe such a theoretical work, which I was able to carry out in the Faculty of Engineering, Kyoto University, and moreover in the Department of Fuel Chemistry, to the encouragement and kind regard of Prof. Shinjiro Kodama, who fostered the Department. What is more, it was the late Prof. Gen-itsu Kita, my life-teacher, and the founder of the Department, who made me enter into chemistry, one of the most attractive and promising fields of science, and led me to devote my whole life to it. For all of these people no words of gratitude can by any means be sufficient. R E F E R E N C E S I. For instance, see Ingold, C. K., Structure and Mechanism in Organic Chemistry, Cornell University Press (1953), Ithaca, N.Y. 2. For instance, see Lewis, G. N., Valence and the Structure of Atoms and Molecules, Chemical Catalog Co. (1923), New York, N.Y. 3. Wheland, G. W. and Pauling, L., J. Am. Chem Soc. 57, 2086 (1935). 4. Coulson, C. A. and Longuet-Higgins, H. C., Proc. Roy. Soc. (London)
(1947).
5. Wheland, G. W., J. Am. Chem. Soc. 64, 900 (1942). 6. Fukui, K., Yonezawa, T. and Shingu, H., J. Chem. Phys. 20, 722 (1952). 7. For instance, see Parr, R. G., The Quantum Theory of Molecular Electronic Structure, Benjamin (1963), New York, N.Y. and references cited therein. 8. Mulliken, R. S., J. Am. Chem. Soc. 74, 811 (1952). 9. Picket, L. W., Muller, N. and Mulliken, R. S., J. Chem. Phys. 21, 1400 (1953). 10. Fukui, K., Yonezawa, T. and Nagata, C., Bull. Chem. Soc. Jpn. 27, 423 (1954); Fukui, K., Kato, H. and Yonezawa, T., ibid. 34, 1112 (1961). 11. Mulliken, R. S., Rec. Trav. Chim. 75, 845 (1956). 12. Fukui, K., Yonezawa, T., Nagata, C. and Shingu, H., J. Chem. Phys. 22, 1433 (1954). 13. For instance, see Fukui, K., Theory of Orientation and Stereoselection, Springer (1970), Berlin.
14. Fukui, K. In: Molecular Orbitals in Chemistry, Physics and Biology, Löwdin, P.-O. and Pullman, B. eds., Academic (1964), New York, N.Y., p. 513. 15. Woodward, R. B. and Hoffmann, R., Angew. Chem. 81, 797 (1969); The Conservation of Orbital Symmetry, Academic Press (1969), New York, N.Y.; see papers In: Orbital Symmetry Papers, Simmons, H. E. and Bunnett,J. F., eds., ACS (1974), Washington D.C. 16. Woodward, R. B. and Hoffmann, R., J. Am. Chem. Soc. 87, 395 (1965). 17. Havinga, E., de Kock, R. J. and Rappoldt, M. P., Tetrahedron 11, 276 (1960); Havinga, E. and Schlatmann, J. L. M. A., ibid. 15, 146 (1961). 18. Hückel, E., Z. Phys. 70, 204 (1931); 76,628 (1932). 19. Fukui, K., Imamura, A., Yonezawa, T. and Nagata, C., Bull. Chem. Soc. Japan 33, 1501 (1960). 20. Heilbronner, E., Tetrahedron Lett., 1964, 1923. 21. Fukui, K., Acc. Chem. Res. 4, 57, (1971). 22. Fujimoto, H., Inagaki, S. and Fukui, K., J. Am. Chem. Soc. 98,2670 (1976). 23. Salem, L., J. Am. Chem. Soc. 90, 543, 553 (1968). 24. Devaquet, A. and Salem, L., J. Am. Chem. Soc. 91, 3743 (1969). K. Fukui 25
26. Bader, R. F. W., Can., J. Chem. 40, 1164 (1962). 27. Pearson, R. G., Symmetry Rules for Chemical Reactions, John Wiley (1976), New York, N.Y. and references cited therein. 28. Klopman, G., J. Am. Chem. Soc. 90, 223 (1968). Also see Klopman, G., Chemical Reactivity and Reaction Paths, John Wiley (1974), New York, N.Y. 29. Herndon, W. C., Chem. Rev. 72, 157 (1972). 30. Hudson, R. F., Angew. Chem. Int. Ed. Eng.
31. For instance, see Dewar, M. J. S. and Dougherty, R. C., The PMO Theory of Organic Chemistry, Plenum (1975), New York, N.Y. and many papers cited therein; see also Dewar, M. J. S., Thetrahedron S8, Part I, p. 85 (1966). 32. Fukui, K. and Fujimoto, H., Bull. Chem. Soc. Japan 41, 1989 (1968). 33. Fukui, K. and Fujimoto, H., Bull. Chem. Soc. Japan 42, 3392 (1969). 34. Fukui, K. In: The World of Quantum Chemistry, Daudel, R. and Pullman, B. eds., Reidel (1974), Dordrecht, p. 113. 35. Fujimoto, H., Yamabe, S. and Fukui, K., Bull. Chem. Soc. Japan 45, 1566 (1972). 36. Fujimoto, H., Yamabe, S. and Fukui, K., Bull. Chem. Soc. Japan 45, 2424 (1972). 37. Yamabe, S., Minato, T., Fujimoto, H. and Fukui, K., Theoret. Chim. Acta (Berl.) 32, 187 (1974).
38. Fujimoto, H., Kato, S., Yamabe, S. and Fukui, K., J. Chem. Phys. 60, 572 (1974). 39. Kato, S., Fujimoto, H., Yamabe, S., Fukui, K., J. Am. Chem. Soc. 96, 2024 (1974). 40. Yamabe, S., Kato, S., Fujimoto, H. and Fukui, K., Bull. Chem. Soc. Japan 46, 3619 (1973); Yamabe, S., Kato, S., Fujimoto, H. and Fukui, K., Theoret. Chim. Acta (Berl.) 30, 327 (1973). 41. Fujimoto, H., Yamabe, S., Minato, T. and Fukui, K., J. Am. Chem. Soc. 94, 9205 (1972). 42. Minato, T., Yamabe, S., Fujimoto, H. and Fukui, K., Bull. Chem. Soc. Japan 51, 1 (1978); Minato, T., Yamabe, S., Fujimoto, H. and Fukui, K., Bull. Chem. Soc. Japan 51, 682 (1978). 43. Baba, H., Suzuki, S. and Takemura, T., J. Chem. Phys. 50, 2078 (1969). 44. Henri-Rousseau, O. and Texier, F., J. Chem. Education 55,437 (1978). 45. For instance, see Hammett, L. P., Physical Organic Chemistry, McGraw-Hill (1940), New York, N.Y. 46. Houk, K. N., Acc. Chem. Res. 8, 361 (1975) and references cited therein. 47. Inagaki, S., Fujimoto, H. and Fukui, K., J. Am. Chem. Soc. 97,6108 (1975). 48. See Fleming, I., Frontier Orbitals and Organic Chemical Reactions, John Wiley (1976), New York, N.Y.; Gilchrist, T. L. and Storr, R. C., Organic Reactions and Orbital Symmetry, Cambridge Univ. Press, 2nd ed. (1979), London. 49. Fukui, K. and Tanaka, K., Bull. Chem. Soc. Japan 50, 1391 (1977). 50. Fukui, K. and Inagaki, S., J. Am. Chem. S OC . 97,4445 (1975) and many papers cited therein. 51. Inagaki, S., Fujimoto, H. and Fukui, K., J. Am. Chem. Soc. 98,4693 (1976). 52. Inagaki, S. and Fukui, K., Chem. Lett. 1974, 509; Inagaki, S., Fujimoto, H. and Fukui, K., J. Am. Chem. Soc. 98, 4054 (1976). 53. Dewar, M. J. S., The Molecular Orbital Theory of Organic Chemistry, McGraw-Hill (1969), New York, N.Y.
55. Fukui, K., Kagaku to Kogyo 29,556 (1976); Hosoya, H., Symposium on Electron Correlation in Molecules, Res. Inst. for Fund. Phys., Dec. 18, 1976. 56. Anderson, P. W., Phys. Rev. 109, 1492 (1958); cf. 1977 Nobel Lectures in Physics by Anderson, P. W., and by Mott, N. F. 57. Goldstein, M. J., J. Am. Chem. Soc. 89,6357 (1967). 58. Simmons, H. E. and Fukunaga, T., J. Am. Chem. Soc. 89, 5208 (1967). 59. Goldstein, M. J. and Hoffmann”, R., J. Am. Chem. Soc. 93,6193 (1971). 60. Hoffman”, R., Imamura, A. and Zeiss, G., J. Am. Chem. Soc. 89, 5215 (1967). 61. For instance, see Hehre, W. J. and Pople, J. A., J. Am. Chem. Soc. 97,694l (1975). 62. Hehre, W. J., Acc. Chem. Res. 8, 369 (1975). 63. For instance, see Glasstone, S., Laider, K. J. and Eyring, H., The Theory of Rate Processes, McGraw-Hill (1941), New York, N.Y. and references cited therein.
26 Chemistry 1981 64. Wang, I. S. Y. and Karplus, M., J. Am. Chem. Soc. 95, 8060 (1973) and references cited therein. 65. Fukui, K., J. Phys. Chem. 74, 4161 (1970). 66. Fukui, K., Kato, S. and Fujimoto, H., J. Am. Chem. Soc. 97, 1 (1975). 67. Kato, S. and Fukui, K., J. Am. Chem. Soc.98,6395 (1976). 68. Tachibana, A. and Fukui, K., Theoret. Chim. Acta (Berl.) 49, 321 (1978). 69. Tachibana, A. and Fukui, K., Theoret. Chim. Acta (Berl.) 51, 189, 275 (1979). 70. Tachibana, A. and Fukui, K., Theoret. Chim. Acta (Berl.) 5, (1979). 71. Fukui, K., Rec. Trav. Chim., Pays-Bas 98, 75 (1979). 72. Joshi, B. D. and Morokuma, K., J. Chem. Phys. 67,488O (1977). 73. Ishida, K., Morokuma, K. and Komornicki, A., J. Chem. Phys. 66, 2153 (1977). 74. Fukui, K., Tachibana, A. and Yamashita, K., Intern. J. Quant. Chem., Quant. Chem. Symp. 15,621 (1981). 75. Miller, W. H., Handy, N. C. and Adams, J. E., J. Chem. Phys. 72, 99 (1980); Gray, S. K., Miller, W. H., Yamaguchi, Y. and Schaefer, H. F., III., ibid. 73, 2732 (1980). 76. Fukui, K., Intern. J. Quant. Chem., Quant. Chem. Symp.
77. Fukui, K., Act. Chem. Res. 14, 363 (1981). 78. Fukui, K., Koga, N. and Fujimoto, H., J. Am. Chem. Soc.
79. Fujimoto, H., Koga, N., Endo, M. and Fukui, K., Tetrahedron Letters 22, 1263; 3427 (1981). 80. Fujimoto, H., Koga, N. and Fukui, K., J. Am. Chem. Soc. 103, 7452 (1981). 81. For instance, see Johnson, K. H. In: The New World of Quantum Chemistry, Pullman, B. and Parr, R. G. eds., Reidel (1976), Dordrecht, p. 317 and references cited therein. 82. Kobayashi, H., Kato, H., Tarama, K. and Fukui, K., J. Catalysis 49, 294 (1977); Kobayashi, H., Yoshida, S., Kato, H., Fukui, K. and Tarama, K., Surface Science 79, 189 (1979). 83. Tanaka, K., Yamabe, T. and Fukui, K., Chem. Phys. Letters 48, 141 (1977). 84. For instance, Schrieffer, J. R. In: The New World of Quantum Chemistry, Pullman, B. and Parr, R. G. eds., Reidel, D., Dordrecht (1976), p. 305; Danese, J. B. and Schrieffer, J. R., Intern. J. Quant. Chem., Quant. Chem. Symp. 10, 289 (1976). 85. Tanaka, K., Yamabe, T., Noda, A., Fukui, K. and Kato, H., J. Phys. Chem. 82, 1453 (1978). 86. Yamabe, T., Tanaka, K., Fukui, K. and Kato, H., J. Phys. Chem. 81, 727 (1977). 87. Tanaka, K., Yamabe, T. and Fukui, K., Chem. Phys. Letters 53, 453 (1978). 88. For instance, see Ishimaru, S., Yamabe, T., Fukui, K. and Kato, H., J. Phys. Chem. 78, 148 (1974); Ishimaru, S., Fukui, K. and Kato, H., Theoret. Chim. Acta (Berl.) 39, 103 (1975). 89. Tachibana, A., Yamabe, T. and Fukui, K., J. Phys. B. Atom. Molec. Phys.
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