The Controversy Between Erich Hückel and Linus Pauling over the Benzene Problem

Karachalios, Andreas

doi:10.1007/978-90-481-3560-8_3

Andreas Karachalios²

Part of the book series: Boston Studies in the Philosophy of Science ((BSPS,volume 283))

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Abstract

Shortly after Hückel’s quantum-theoretical work on the problem of aromatic compounds was published, the first paper on the same subject by the American Linus Pauling also appeared. It was the fifth installment of a total of seven that Pauling published between April 1931 and July 1933 under the general title The Nature of the Chemical Bond.This fifth part was the first coauthored with his pupil George Wheland, a National Research Fellow in Pasadena. In their quantum mechanical treatment of benzene, naphthaline and free organic radicals, they applied a “VB” approximation slightly different from Hückel’s “first method” yet sharing some resemblance with it. The two subsequent parts of Pauling’s series were copublished with John Sherman. These authors analysed thermochemical data to calculate the resonance energies of a large number of organic molecules, aromatic and conjugated systems

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Notes

1.
Pauling, L., Wheland, G.: The Nature of the Chemical Bond. V. The Quantum Mechanical Calculation of the Resonance Energy of Benzene and Naphthalene and the Hydrocarbon Free Radicals, in: JCP 1 (1933), 362–374.
2.
Pauling, L.: The Nature of the Chemical Bond. Application of Results Obtained from the Quantum Mechanics and from a Theory of Paramagnetic Susceptibility to the Structure of Molecules, in: JACS 53 (1931), 1367–1400; The Nature of the Chemical Bond. II. The One – Electron Bond and the Three – Electron Bond, in: JACS 53 (1931), 3225–3237; The Nature of the Chemical Bond. III. The Transition from one Extreme Bond Type to Another, in: JACS 54 (1932), 988–1003; The Nature of the Chemical Bond. IV. The Energy of Single Bonds and the Relative Electronegativity of Atoms, in: JACS 54 (1932), 3570–3582; Pauling, L., Sherman, J.: The Nature of the Chemical Bond. VI. The Calculation from Thermochemical Data of the Energy of Resonance of Molecules Among Several Electronic Structures, in: JCP 1 (1933), 606–617; The Nature of the Chemical Bond. VII. The Calculation of Resonance Energy in Conjugated Systems, in: JCP1 (1933), 679–686.
3.
Pauling, L., Wheland, G.: The Nature of the Chemical Bond. V., p. 363.
4.
Hückel, E.: Grundzüge der Theorie ungesättigter und aromatischen Verbindungen, in: Zeitschr. Elektrochem. 43 (1937), 752–788, p. 759.
5.
Ibid.
6.
Pauling, L., Wheland, G.: The Nature of the Chemical Bond. V., p. 364.
7.
Pauling, L.: The Calculation of Matrix Elements for Lewis Electronic Structures of Molecules, in: JCP 1 (1931), 280–283.
8.
At the end of his paper Pauling underscored the usefulness of the above-mentioned methods: “The methods developed in this paper have been applied in a discussion of the structure of aromatic substances, free radicals, etc., to be published soon…” Ibid., p. 283. In the subsequent literature, the approximative method Pauling used is referred to as the valence-bond (VB) or Heitler-London-Slater-Pauling (HLSP) method.
9.
See Section 2.2.1.
10.
Born, M.: Zur Quantentheorie der chemischen Kräfte, in: ZP 64 (1930), 729–740.
11.
Heitler, W.: Zur Gruppentheorie der homöopolaren chemischen Bindung, in: ZP 47 (1928), 835–858.
12.
About Heitler’s interest about group theory and their applications to the problems of chemical valence see: Gavroglu, K.: Fritz London: A Scientific Biography. Cambridge University Press, Cambridge, 1995, Chap. 2, Polyelectronic Molecules and the Application of the Group Theory to Problems of Chemical Valence, pp. 53–57; Gavroglu, K., Simoes, A.: The Americans, the Germans, and the Beginnings of Quantum Chemistry: The Confluence of Diverging Traditions, in: Historical Studies in the Physical Sciences 25(1) (1994), 47–110, Polyelectronic Molecules and Group Theory, pp. 66–70.
13.
Born, M.: Zur Quantentheorie der chemischen Kräfte, p. 729.
14.
Heitler, W., Rumer, G.: Quantentheorie der chemischen Bindung für mehratomige Moleküle, in: ZP 68 (1931), 12–41. A preliminary version of the paper appeared under the title “Quantenchemie mehratomiger Moleküle” in: Nachrichten von der königlichen Gesellschaft der Wissenschaften zu Göttingen. Mathematisch-physikalische Klasse aus dem Jahre, 1930, pp. 277–284.
15.
Ibid., p. 24.
16.
Weyl, H.: Zur quantentheoretischen Berechnung molekularer Bindungsenergien, in: Nachrichten von der königlichen Gesellschaft der Wissenschaften zu Göttingen. Mathematisch-physikalische Klasse aus dem Jahre, 1930, pp. 285–294; Zur quantentheoretischen Berechnung molekularer Bindungsenergien. II, in: Nachrichten von der königlichen Gesellschaft der Wissenschaften zu Göttingen. Mathematisch-physikalische Klasse aus dem Jahre, 1931, pp. 33–39.
17.
Heitler, W., London, F.: Wechselwirkung neutraler Atome und homöopolare Bindung nach der Quantenmechanik, in: ZP 44 (1927), 455–472.
18.
London, F.: Zur Quantentheorie der homöopolaren Valenzzahlen, in: ZP 46 (1928), 455–477; Zur Quantenmechanik der homöopolaren Valenzchemie, in: ZP 50 (1928), 24–51. Heitler, W.: Zur Gruppentheorie der homöopolaren chemischen Bindung, in: ZP 47 (1928), 835–858. See also Heitler’s summary: Heitler, W.: Der gegenwärtige Stand der quantenmechanischen Theorie der homöopolaren Bindung, in: PZ 31 (1930), 185–204. In these papers Heitler formulated an approximation for the binding energy between two arbitrary atoms that, as he emphasized, corresponded to the formation of an electron pair of two electrons belonging to different atoms, hence corresponding to the “chemical valence line”: A series of states result in which one, two or more pairs of electrons become saturated until all of an atom’s valence electrons are used up.
19.
Weyl, H.: Zur quantentheoretischen Berechnung molekularer Bindungsenergien. II, in: Nachrichten von der königlichen Gesellschaft der Wissenschaften zu Göttingen. Mathematisch-physikalische Klasse aus dem Jahre (1931), 33–39, p. 36 (Original emphasis.)
20.
Much earlier, various 19th-century mathematicians had noticed this formal similarity between the valence-line diagram in chemistry and binary invariant theory. They realized that the combinatorics of valences used in the construction of chemical formulas, particularly in determining possible isomers, was the same as the combinatorial techniques in the mathematical area of invariant theory of binary forms. The first papers along these lines were written by the American Jean Joseph Sylvester and the English mathematician William Kingdon Clifford, who published the results of their research 1878 in the first volume of the journal Sylvester had founded, American Journal of Mathematics Pure and Applied, at the Johns Hopkins University in Baltimore. They were succeeded by the German theoretician of invariants Paul Gordan and the Russian chemist W. Alexejeff. Cf. Sylvester, J. J.: On the Application of the New Atomic Theory to the Graphical Representation of the Invariants and Covariants of Binary Quantics, in: American Journal of Mathematics 1 (1878), 64–90; Clifford, W. K.: Extract of a Letter to Mr. Sylvester from Prof. Clifford of University College, London, in: American Journal of Mathematics 1 (1878), 126–128; Gordan, P., Alexejew, W.: Übereinstimmung der Formeln der Chemie und der Invariantentheorie, in: ZPC 35 (1900), 610–633; Alexejeff, W.: Über die Bedeutung der symbolischen Invariantentheorie für die Chemie, in: ZPC 36 (1901), 741–743. Sylvester first noticed a similarity between invariant theory and the then still young atomistic theory of chemistry. Clifford elaborated on this insight and developed his own symbolical representation for various molecular compositions. Gordan and Alexejeff, for their part, expanded on the relation between the concepts and formulas used in chemistry and formulas of invariant theory. They showed that the formal methods of the symbolical theory of invariants were well suited to addressing the formal questions of modern chemistry and had close associations with the methods employed by atomistic structural theory in chemistry. Alexejeff’s analyses offer this latter theory new tools for solving some formal questions, such as calculating the number of isomers and their structures. Chemists took little notice of these papers, however. Weyl provides the following reason: “Nevertheless, chemists stood by their familiar valence diagrams, for there was no physical interpretation for the addition of invariants and for dynamic laws by which the binding powers and the real stationary states could be determined. Today we can see that only such a radical new direction as the quantum mechanics can reveal the significance of the picture that Sylvester discovered as a purely formal, albeit very impressive mathematical analogy.” See Weyl, H.: Philosophie der Mathematik und Naturwissenschaft. R. Oldenburg Verlag, München, 1990, Anhang D: Die chemische Valenz und die Hierarchie der Strukturen, p. 351. The papers by Weyl and Rumer mentioned above were actually the primary movers toward this “radical new direction.”
21.
This interpretation is entirely valid for diatomic molecules and for the special class of polyatomic molecules with additive binding energies. But difficulties immediately arise with other polyatomic molecules with nonadditive energies. Cf. Heitler, W.: Quantentheorie und homöopolare chemische Bindung, in: Handbuch der Radiologie Band VI, Quantenmechanik der Materie und Strahlung, Teil II Moleküle. Akademische Verlagsgesellschaft M. B. H., Leipzig, 1934, pp. 485–586.
22.
Weyl, H.: footnote 19, p. 36.
23.
The Karpov Institute of Physical Chemistry was founded on October 4, 1918 in Moscow as a central chemistry laboratory. It was named after the first director of the Soviet chemical industry, Lev Jakovlevich Karpov. This institute enjoyed much political support because the research conducted at the institute was considered of military and economic importance for the development of the nation. During the 1930s there were eight different departments of physical chemistry. Rumer worked in the theoretical department. Since 1934 it was directed by the German pioneer of quantum chemistry Hans G. A. Hellmann (1903–1938) who had emigrated from Germany for political reasons to Moscow. His wife was Jewish. In March 1938 he was arrested in a Stalinist purge as a purported Germany spy, condemned to death in May and shot on May 29, 1938. On October 15, 1957, he and his family were exonerated. Hellmann’s scientific career and personal fate is covered in Schwarz, W. H. E., Karachalios, A. u. a.: Hans G. A. Hellmann (1903–1938) I. Ein Pionier der Quantenchemie, in: Bunsen-Magazin 1 (1999), 10–21; II. Ein deutscher Pionier der Quantenchemie in Moskau, in: Bunsen-Magazin 1 (1999), 60–70.
24.
Rumer, G.: Zur Theorie der Spinvalenz, in: Nachrichten von der königlichen Gesellschaft der Wissenschaften zu Göttingen. Mathematisch-physikalische Klasse aus dem Jahre, 1932, pp. 337–341. Rumer’s paper was presented before the society at the meeting on July 22, 1932 by H. Weyl.
25.
Ibid., p. 338 (emphasis mine). By this method one obtains a complete system of independent valence states. Rumer later provided the mathematical basis in a paper written together with Teller and Weyl. See Rumer, G., Teller, E., Weyl, H.: Eine für die Valenztheorie geeignet Basis der binären Vektorinvarianten, in: Nachrichten von der königlichen Gesellschaft der Wissenschaften zu Göttingen. Mathematisch-physikalische Klasse aus dem Jahre, 1932, pp. 449–504.
26.
Rumer, G.: Zur Theorie der Spinvalenz, p. 338.
27.
The conceptual differences and specifics mentioned above play a decisive role in Hückel’s criticism of Pauling’s concept of resonance. See Section 3.3 below.
28.
For more details on this problem see Born, M.: Chemische Bindung und Quantenmechanik, in: Ergebnisse der Exakten Naturwissenschaften, 10 (1931), 387–444. Born’s survey article sought to introduce physicists and chemists to Weyl’s basic ideas sketched above. This purpose is spelled out in the introduction: “Weyl apparently views these results as quite insignificant side-products of his major papers on group theory, and he also published them in so brief and inconspicuous a form that it is hard to understand. For us physicists and chemists they are, on the other hand, so important that it would seem appropriate to describe the conclusions at least in an easily comprehensible form. The proofs are not suitable for this because Slater and the author have not managed here to completely avoid the “group plague.” But I suppose the practitioner will be able to suffer this if the concepts and calculational methods are offered in an understandable and usable form: the chemist conducts his experiments according to prescribed rules and recipes, so he will be willing to calculate according to prescribed rules as well.”
In an effort to promote the new quantum theory of chemical bonds among chemists, Born also delivered two talks: the first on June 23, 1932, at the district affiliate in Hannover of the Verein Deutscher Chemiker and the second on February 11, 1933 in Berlin before the Deutschen Chemischen Gesellschaft. Cf. Born, M.: Zur Theorie der homöopolaren Valenz bei mehratomigen Molekülen, in: Angewandte Chemie 45 (1932), 6–8; Welche Vorstellung von der chemischen Bindung vermittelt die Quantenmechanik?, in: Angewandte Chemie 46 (1933), 179–180.
29.
Ibid.
30.
The formalisms were later simplified and presented in a more understandable form in order also to serve chemists. It was later shown, however, that the simplified version of the theory was inconsistent and a few parts were conspicuously wrong, causing this avenue to become irrelevant. Cf. Kutzelnigg, W.: Einführung in die Theoretische Chemie, Band 2, 1994, pp. 3–4.
31.
AHQP, Interview with Heitler, 19 March 1963, p. 2.
32.
Heitler, W.: Quantum Theory and Electron Pair Bond, in: Physical Review 38 (1931), 243–247.
33.
Ibid., p. 243 (original English, emphasis mine).
34.
Ibid., p. 244 (emphasis in the original English).
35.
Ibid., p. 245f.
36.
Cf. Heitler, W.: Quantentheorie und homöopolare chemische Bindung, in: Handbuch der Radiologie Band VI, Quantenmechanik der Materie und Strahlung, Teil II Moleküle. Akademische Verlagsgesellschaft M. B. H., Leipzig, 1934, pp. 485–586.
37.
Ibid., p. 572.
38.
Pauling, L.: The` Calculation of Matrix Elements for Lewis Electronic Structures of Molecules, in: JCP 1 (1933), 280–283, p. 281.
39.
Ibid.
40.
Pauling, L.: The Nature of the Chemical Bond. V., p. 364.
41.
In their paper Pauling and Wheland point out in this regard: “Hence the extra energy of the molecule resulting from resonance among the five independent structures is 1.1055α. It is interesting to see how much of this extra energy is due to resonance between the two Kekulé structures and how much is contributed by the excited structures C, D and E. A simple calculation shows that 0.9α or approximately 80 percent of the resonance energy comes from the Kekulé structures alone and only about 20 percent from the three excited structures.” Ibid., pp. 364–365.
42.
Kutzelnigg, W.: Friedrich Hund und die Chemie, in: Angewandte Chemie 108 (1996), 629–643, p. 631. About Pauling’s bold simplifications, contradictory and sometimes confused descriptions as well as the ambiguity about the physical reality of “canonical structures,” see Park, B. S.: Chemical Translators: Pauling, Wheland and their Strategies for Teaching the Theory of Resonance, in: British Journal for the History of Science 32 (1999), pp. 21–46; Simoes, A.: Converging Trajectories, Diverging Traditions, p. 169.
43.
Pauling and Wheland stated: “The results of the calculation for benzene are (...) identical with those obtained by Hückel.” Cf. Pauling, L., Wheland, G.: The Nature of the Chemical Bond. V., p. 365.
44.
SBPK, Papers of Erich Hückel, Box 6, Folder 5. 213, Letter Hückel to Pauling, Stuttgart (Bad Cannstatt), 28.12.1933.
45.
Hückel, E.: Gründzüge der Theorie ungesättigter und aromatischer Verbindungen, in: Z. Elektrochem. 43 (1937), 752–788, p. 759.
46.
SBPK, Papers of Erich Hückel, Box 6, Folder 5. 213, Letter Hückel to Pauling, Stuttgart (Bad Cannstatt), 28.12.1933.
47.
SBPK, Papers of Erich Hückel, Box 6, Folder 5. 115, Letter Pauling to Hückel, California Institute of Technology, Pasadena, April 17, 1934. (original English).
48.
Pauling, L., Wheland, G.: The Nature of the Chemical Bond. V., p. 365.
49.
SBPK, Papers of Erich Hückel, Box 6, Folder 5. 12, Letter Sir William Bragg to Hückel, 18 May, 1934.
50.
Hückel, E.: Aromatic and Unsaturated Molecules: Contributions to the Problem of their Constitution and Properties, in: International Conference on Physics, Paper and Discussions, The Physical Society, London, 1935. The University Press, Cambridge, 1935, vol. II, pp. 9–35.
51.
Hund, F.: Description of the Binding Forces in Molecules and Crystal Lattices on Quantum Theory, in: International Conference on Physics, Paper and Discussions, The Physical Society, London, 1935. The University Press, Cambridge, 1935, vol. II, 36–45.
52.
Hückel, E.: Aromatic and Unsaturated Molecules, p. 15. (original English).
53.
Ibid., pp. 15–20. Hückel had conveyed some of his points of criticism to Pauling prior to the conference in London in a letter dated July 25, 1934, requesting “a prompt reply.” No documentation has yet been found on whether Pauling wrote in reply.
54.
Hund, F.: Description of the Binding Forces in Molecules and Crystal Lattices on Quantum Theory, in: International Conference on Physics, Paper and Discussions, The Physical Society, London, 1935. The University Press, Cambridge, 1935, vol. II, 37–38 (emphasis mine.)
55.
From among the abundant literature on this aspect, we refer to the following important paper and further references there. Francoeur, E.: Molecular Models and the Articulation of Structural Constraints in Chemistry, in: Tools and Modes of Representation in the Laboratory Sciences, ed. by Ursula Klein. Kluwer Academic Publishers, Dordrecht/Boston/London, 2001, pp. 95–115; Hoffmann, R. und Laszlo, P.: Darstellungen in der Chemie – die Sprache der Chemiker, in: Angewandte Chemie 103 (1991), 1–16.
56.
Cf. Gavroglu, K., Simoes, A.: The Americans, the Germans and the Beginning of Quantum Chemistry (1994).
57.
Nye, M. J.: Paper Tools and Molecular Architecture in the Chemistry of Linus Pauling, in: Tools and Modes of Representation in the Laboratory Sciences, edited by Ursula Klein. Kluwer Academic Publishers, Dordrecht/Boston/London, 2001, pp. 117–132.
58.
Slater, J. C.: Discussion on the Structure of Molecules and of the Ideal Lattice, in: International Conference on Physics, Paper and Discussions, The Physical Society, London, 1935. The University Press, Cambridge, 1935, vol. II, p. 53.
59.
Ibid.
60.
SBPK, Papers of Erich Hückel, Box 6, Folder 5. 117, Letter Richter to Hückel, Berlin, 28 Oktober, 1935.
61.
Ibid.
62.
Ibid.
63.
Pauling formulated this postulate in his paper: The Additivity of the Energies of Normal Covalent Bonds, which he submitted on 9 May 1932 to the Proceedings of the National Academy of Sciences of the United States of America: “In the wave function representing the bond between unlike atoms A and B, the ionic term A⁺B^– and A^–B⁺ will occur with the same coefficient, of the order of magnitude of those for A:A and B:B, if the two atoms have the same degree of electronegativity. We propose to call such a function a normal covalent bond wave function, and the bond a normal covalent bond; and to make the postulate that the energies of normal covalent bonds are additive, that is, A:B = 1/2 (A:A + B:B), where the symbols A:B, etc., mean the energies of the normal covalent bonds. This postulate requires that the energy change for a reaction such as 1/2 A₂ + 1/2 B₂ = AB involving only normal covalent substances with single bonds be zero.” Cf. Pauling, L., Yost D. M.: The Additivity of the Energies of Normal Covalent Bonds, in: Proceedings of the National Academy of Sciences of the United States of America 18 (1932), 414–416 (original emphasis). Details about the importance of this postulate in the development of Pauling’s research agenda on the nature of chemical bonding and his theory of resonance are given in Weininger, S. J.: Affinity, Additivity and the Reification of the Bond, in: Tools and Modes of Representation in the Laboratory Sciences, edited by Ursula Klein. Kluwer Academic Publishers, Dordrecht/Boston/London, 2001, pp. 237–251; Simoes, A.: Converging Trajectories, Diverging Traditions (1993), pp. 156–158.
64.
Hückel enclosed with his letter to Ritter a separatum of his London talk in which he laid out in detail the experimental data used to calculate the energy content of the various aromatic compounds.
65.
SBPK, Papers of Erich Hückel, Box 6, Folder 5. 214, Letter Hückel to Richter, Stuttgart, 31 Oktober, 1935.
66.
Hückel, E.: Grundzüge der Theorie ungesättigter und aromatischer Verbindungen, in: Z. Elektrochem. 43 (1937), 752–788; 43 (1937), 827–849.
67.
With it are meant the [p]_h-Elektronen or π-Elektronen.
68.
Hückel, E.: Grundzüge der Theorie ungesättigter und aromatischer Verbindungen, p. 758 (original emphasis).
69.
For more details see Section 2.2.2 above.
70.
Hückel, E.: Grundzüge der Theorie ungesättigter und aromatischer Verbindungen, p. 758.
71.
As Pauling’s concept of resonance has already been thoroughly discussed by Gavroglu, Park and Simones, this section will only be concerned with Hückel’s critique against Pauling. Cf. Park, B. S.: Chemical Translators: Pauling, Wheland and their Strategies for Teaching the Theory of Resonance, in: British Journal for the History of Science 32 (1999), 21–46; Computations and Interpretations: The Growth of Quantum Chemistry, 1927–1967, Dissertation, John Hopkins University, Baltimore, Maryland, 1999; Simoes, A.: Coverging Trajectories, Diverging Traditions (1993); Simoes, A., Gavroglu, K.: Issus in the History of Theoretical and Quantum Chemistry, 1927–1960, in: Chemical Sciences in the 20th Century, edited by Carsten Reinhardt. Wiley-VCH, Weinheim, 2001; Mosini, V.: A Brief History of the Theory of Resonance and its Interpretation, in: Studies in History and Philosophy of Modern Physics 31B(4) (2000), 569–581.
72.
Hückel, E.: Grundzüge der Theorie ungesättigter und aromatischer Verbindungen, p. 763.
73.
Ibid.
74.
Ibid.
75.
Ibid.
76.
Ibid., p. 767.
77.
Ingold, C. K.: Principles of an Electronic Theory of Organic Reactions, in: Chemical Reviews 15 (1934), 225–274; Mesomerism and Tautomerism, in: Nature 133 (1934), 946–947. On Ingold’s career in science and his contributions to the concept of “mesomerism” as well as to structures and mechanisms in organic chemistry as a whole, see Shoppee, C. W.: Christopher Kelk Ingold, in: Biographical Memoirs of Fellows of the Royal Society 18 (1972), 349–411; Nye, M. J.: From Chemical Philosophy to Theoretical Chemistry, Chap. 8, Reaction Mechanisms: Christopher Ingold and the Integration of Physical and Organic Chemistry, 1920–1950, pp. 196–225; Remodeling a Classic: The Electron in Organic Chemistry, 1900–1940, in: Histories of the Electron, The Birth of Microphysics, edited by Jed Z. Buchwald and Andrew Warwick. The MIT Press, Cambridge, Massachusetts, 2001; Schofield, K.: The Development of Ingold’s System of Organic Chemistry, in: Ambix 41 (1994), 87–107; Brock, W. H.: The Norton History of Chemistry, Chap. 14; Saltzmann, M.: C. K. Ingold’s Development of the Concept of Mesomerism, in: Bulletin for the History of Chemistry 19 (1996), 25–32.
78.
Arndt, F., Eistert, B.: Über den “Resonanz” – und “Zwischenstufen” – Begriff bei organischen Substanzen mit mehrfachen Bindungen und die Elektronenformeln, in: ZPC-B 31 (1935), 125–131.
Fritz Arndt, born in Hamburg on July 6, 1885, was one of the few organic chemists in Germany occupied with theoretical issues on chemical bonding. From 1919 he was supernumerary professor of organic chemistry at Breslau, receiving tenure in 1928, only to be dismissed in 1933 as a “non-Aryan.” Soon afterwards, the Turkish state officially invited German professors seeking asylum to come to Istanbul. Arnst was one of 19 German professors whose scientific exchanges with Turkey date back to after World War I, when the German and Ottoman Empires were allies. He received an appointment to the newly founded “Istanbul Universitesi” on August 1, 1933, where he built up a laboratory of organic chemistry. He and his students examined tautomerizable systems, proving the effectiveness of methylation with diazomethane. These analyses led to a distinction between static and dynamic acidity.
Eistert was a long-time collaborator of Arndt, maintaining contacts with him after his emigration. They copublished a number of papers until 1941. One was the paper just mentioned, in which the “resonance concept” was described in terms of a theory of “intermediate stages” that Arndt had derived 11 years earlier out of purely chemical considerations. In his paper “On dipyrylenes and on the binding relations in pyrone ring systems,” published in the Berichte of 1924, he found that the chemical behavior of pyrones could not be correctly expressed either by formula I or by the “bonding isomers” zwitterion formula II. It was an “intermediate state” between the two extremes represented by the formulas:
Fig 3

Cf. Arndt, F., Scholtz, E., Nachtwey, P.: Über Dipyrylene und über die Bindungsverhältnisse in Pyron-ringsystemen, in: B 57 (1924), 1903–1911. Arndt imagined this state as an “intermediate stage” between formulas I and II. Arndt’s proposed theory of “intermediate stages” proved fruitful in explaining the chemical and physical behaviors of many other organic categories of substances, such as the carbon amide and thiamide groups and polybonded cations. See Walter, W., Eistert, B.: Fritz Arndt (1885–1969), in: CB 108 (1975), I–XLIV; Campaigne, E.: The Contributions of Fritz Arndt to Resonance Theory, in: Journal of Chemical Education 36 (1959), 336–339; Üstün, A.: Zweites Vaterland – deutsche Chemiker im türkischen Exil, in: Nachrichten aus der Chemie 51 (2003), 152–155; Burk, L. A.: Fritz Arndt and his Chemistry Books in the Turkish Language, in: Bulletin for the History of Chemistry 28 (2003), 42–52.
79.
Bernd Eistert was born on November 9, 1902 in the regional Slask town of Ohlau near Breslau. 1922 he took up the study of chemistry at the University of Breslau. The director and chair of the institute there was the inorganic chemist Heinrich Biltz. Julius Meyer was extraordinary professor of inorganic chemistry and Fritz Arndt was a private lecturer in the faculty. Eistert took his doctorate under Arndt 1927 on chain extension in carboxylic acids. On Arndt’s recommendation he became assistant of the complex chemist Paul Pfeifer in Bonn on November 1, 1928, and in 1929 he was employed at the main laboratory of BASF in Ludwigshafen. He remained in touch with Arndt and continued to work on such theoretical problems as tautomerism and mesomerism, the chemism of Claisen condensation, etc. Eistert’s interest in theory prompted exchanges with Erich Hückel about Hückel’s survey article “Grundzüge der Theorie ungesättigter und aromatischer Verbindungen” mentioned above as well as on Eistert’s own successful book “Tautomerie und Mesomerie”. Cf. Regitz, M., Heydt, H., Schank, K. und Franke, W.: Bernd Eistert (1902–1978), in: Chemische Berichte 113 (1980), XXIX–LVIII.
80.
Hückel, E.: Grundzüge der Theorie ungesättigter und aromatischer Verbindungen, p. 764. Hückel cited in his article the following papers by Ingold, Arndt and Eistert: Ingold, C. K.: Principles of an Electronic Theory of Organic Reactions, in: Chemical Reviews 15 (1934), 225–274, insbesondere S. 250–252; Arndt, F., Eistert, B.: Über den Chemismus der Claisen-Kondensation, in: B 69 (1936), 2381–2398.
81.
Ibid. (emphasis mine).
82.
Pauling, L.: The Nature of the Chemical Bond and the Structure of Molecules and Crystals: An Introduction to Modern Structural Chemistry. Cornell University Press, New York, 1939, p. 10, footnote 1. Hückel then criticized the previously quoted passage from Pauling’s book, emphasizing the contradictory meaning of the term “structure”: “Here in one and the same sentence Pauling uses two meanings for the word ‘structure’: once with the meaning a diagram that is assigned to a specific function that can (but does not have to!) be used as one of the initial functions for the perturbation calculation; the other time, to designate the real state of the molecule; for such functions are not changed anymore. Only specific linear combinations are sought, in particular those that lead to the lowest energy in the perturbation calculation.” Cf. Hückel, E.: Zur modernen Theorie ungesättigter und aromatischer Verbindungen, in: Z. Elektrochem. 61 (1957), 866–890, p. 873. (original emphasis).
83.
Ibid.
84.
Hückel, E.: Zur modernen Theorie ungesättigter und aromatischer Verbindungen, in: Z. Elektrochem. 61 (1957), 866–890.
85.
Ibid., pp. 872–873.
86.
Ibid., p. 873 (emphasis mine).
87.
Ibid., p. 871 (emphasis mine).
88.
Ibid., p. 871, footnote 19.
89.
According to Slater, they can be written in the form of determinants. Thus they are also known as “Slater functions” or “Slater determinants.”
90.
Ibid.
91.
Cf. Heitler, W.: Quantum Chemistry: The Early Period, in: International Journal of Quantum Chemistry 1 (1967), 13–36, p. 34, footnote 4.

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Andreas Karachalios

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Karachalios, A. (2010). The Controversy Between Erich Hückel and Linus Pauling over the Benzene Problem. In: Erich HÜckel (1896–1980). Boston Studies in the Philosophy of Science, vol 283. Springer, Dordrecht. https://doi.org/10.1007/978-90-481-3560-8_3

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DOI: https://doi.org/10.1007/978-90-481-3560-8_3
Published: 06 November 2009
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