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Radicals, Reactions, Realism

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Philosophy of Chemistry

Part of the book series: Boston Studies in the Philosophy and History of Science ((BSPS,volume 306))

Abstract

Since Lavoisier, the notion of radical has been used – and is still being used – in chemistry. It first was assigned to the assumed “acidic” core of acids, later to certain assumed fragments of substances or molecules (some of which became “functional groups”), and today – after the introduction of electronic configurations and quantum chemistry – every chemical entity with unpaired electrons is called a radical. Most radicals (in the modern sense) are unstable and at best intermediate chemical species but no proper substances at all. However, in the historical archives of organic chemistry Moses Gomberg is described as the very first researcher who (in 1900) synthesized a stable radical, namely triphenylmethyl. Although (or just because) this in fact was not really true, the episode of that synthesis is an interesting target to investigate in order to draw lessons from it regarding the history and philosophy of chemistry, particularly the understanding of chemical substances. This study delivers an attempt to clarify the epistemological status of the radical concept during the “synthetic period” at the beginning of the twentieth century, the related existence claims, and the specific role of the applied experimentation.

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Notes

  1. 1.

    I will call the period of empirical and preparative success which begins with Gomberg’s work the synthetic period, which came after the speculative period and was followed by the electronic period of radical chemistry.

  2. 2.

    Ihde 1967, 5. Reference is made to Gomberg 1900a, the English version of which is Gomberg 1900b. Gay 1976 offers an investigation of what is called the prehistory of the radical concept here. She critically accounts for the methodological approaches of Popper and Lakatos referring to the historical example mentioned here.

    It has been suggested – to add another note referring to the history of radical theory from an extremely modernistic point of view – to consider and accept Michael Faraday as the discoverer of free radicals, see Acheson 1996.

  3. 3.

    Cf. the biographical entries in Schoepfle and Bachmann 1948; Bailar 1970; Rüchardt 2000.

  4. 4.

    The experimental setup is described in Gomberg 1897.

  5. 5.

    Gomberg 1914, 1156.

  6. 6.

    In his well-known textbook on reaction mechanisms, Peter Sykes states: “Hexaphenylethane has not, indeed, ever been prepared, and may well be not capable of existing under normal conditions due to the enormous steric crowding that would be present.” (Sykes 1986, 301)

  7. 7.

    C.f. Fieser and Fieser 1968, 410.

  8. 8.

    See Lankamp et al. 1968. See also Nair et al. 2006.

  9. 9.

    Cf. in the preface of his chemistry textbook Berzelius 1825.

  10. 10.

    Well-known examples (from modern chemistry) are the nitrogen oxides NO and NO2. The most fascinating exception of the group of instable or intermediate radicals is dioxygen, O2. The molecules of this (normal) allotrope of oxygen contain two unpaired electrons and are reasonably stable. Accordingly most modernist attempts to set up a historical order for the development of the radical concept look like the following of Rüchardt 1992: 1787–1900 Period of the clarification of notion; 1900–1945 Period of discoveries; 1945 – today Period of theoretical achievement and successful application. In another article the same author even classifies a single electron as radical (Rüchardt and Mayer-Ruthardt 1969, 41).

  11. 11.

    From a modern point of view the trivalency is not a prerequisite for a radical status of a substance. Carbon monoxide, CO, for example, is described as having a triple bond in quantum chemistry, and nevertheless it is not a radical (e.g. it is diamagnetic in the ground state).

  12. 12.

    The formation of which is reversible (expressed by color changes). (C6H5)6C − O − O − C(C6H5)6 comes to 88.0 % C and 5.8 % H.

  13. 13.

    Gilbert Lewis (1875–1946) seems to have introduced the radical concept of unpaired electrons and the paramagnetism of such radicals (Lewis 1923).

  14. 14.

    Note that the original “Radikal” with the description referred to here was translated into “radicle”, see the 2nd ed. (Ostwald 1904, 406).

  15. 15.

    Gomberg 1928, 163. Presumably Gomberg’s formulation inspired Ihde when he wrote his statement cited at the introduction of the present contribution.

  16. 16.

    Gomberg gives an account of this scientific struggle in Gomberg 1914. That paper is the first in which he used the expression radical in a title.

  17. 17.

    Cf. the title of McBride 1974.

  18. 18.

    A surveying account of work and life of Wilhelm Schlenk is given in Tidwell 2001.

  19. 19.

    Gomberg 1928, 164. In his monograph on philosophy of chemistry, the Dutch philosopher Jaap van Brakel refers to a similar view. In a footnote referring to discussions of USSR philosophers of chemistry such as Kedrov he states: “Here, the material carriers of chemical change are assumed to be atoms, molecules, radicals and ions (both of atoms and atom groups)”, van Brakel 2000, 25.

  20. 20.

    Note that in fact any analytical work incorporates necessary synthetic steps, that is, the “analytical” methodology like in Schummer’s description should be read theoretically rather than empirically.

  21. 21.

    Note that this is the case for many pure substances, for example the chemical elements during the very first occasion of their discovery or preparation.

  22. 22.

    Timmermans 1940, 5.

  23. 23.

    Here of course reference is made to Hacking’s entity realism and van Fraassen’s constructive empiricism. We will return to both later. – It has to be noted that the mentioned ethyl radical – at least what might be called its empirically adequate correlate – eventually came into life in the 1930s, when Friedrich Paneth and his co-workers arranged to have determined short-lived methyl and ethyl radicals in ingenious experimental set-ups (Paneth and Lautsch 1930). This intriguing story and its specific philosophical background will be discussed elsewhere.

  24. 24.

    Van Brakel stresses this classical empiricist claim in his textbook van Brakel 2000.

  25. 25.

    In his survey, Gomberg, referring to the “uninterrupted progress” of fixed quadrivalence of carbon, cites this passage (Gomberg 1932, 443).

  26. 26.

    Cf. Ruthenberg 2008b for a short discussion of this episode from the history of the philosophy of chemistry.

  27. 27.

    The author has not found an explicit reference of Ostwald’s to Gomberg’s radical. In his Principles from 1909, Ostwald still referred critically to the expression radical as a formal and structural grouping concept without mentioning concrete examples (Ostwald 1909, 325).

  28. 28.

    Ostwald said that if two bodies have some specific properties in common then all other specific properties will turn out to be identical, too: “…wenn bei zwei Körpern einige spezifische Eigenschaften übereinstimmen, dann erweisen sich auch alle anderen spezifischen Eigenschaften übereinstimmend.” (Ostwald 1907, 74–75)

  29. 29.

    Cf. van Brakel 2013.

  30. 30.

    Ruthenberg 2009, 75–76.

  31. 31.

    Ruthenberg 2008a, 59 (emphases original).

  32. 32.

    van Fraassen 1984, 250.

  33. 33.

    Walden 1924, 3

  34. 34.

    See, for example, Gomberg 1925. Even more so in modern scientific papers: “The experimental demonstration of the existence of the triphenylmethyl radical by Gomberg is a milestone in the development of mechanistic organic chemistry.” (Nair et al. 2006)

  35. 35.

    The author writes: “I believe that science disposes of three different methodologies, each appropriate to the study of a specific domain of beings, both natural and cultural.” (Harré 1986, 70)

  36. 36.

    Harré 1986, 70–71. The author claims that the vast majority of scientific theories are of type 2.

  37. 37.

    A fact that lets the approach of constructive empiricism of Bas van Fraassen appear sympathetic, because to care for empirical adequacy is less ambitious than to change his or her belief whenever a theory develops or changes. Cf. van Fraassen 2001.

  38. 38.

    The radical concept has run through several significant changes (for discussions of the nineteenth century developments see Gomberg 1932; Gay 1976; Rocke 1984). Therefore it is questionable to speak about “the one” radical theory due to “translation” problems (not to speak of possible incommensurabilities). There is indeed no significant sense to describe this history as linear story of success (as textbooks and modern literature sometimes do).

  39. 39.

    Early theoretical works in the twentieth century are Pauling and Wheland 1933; Hückel 1934; Ingold 1934. Intriguingly, the latter explicitly discusses “chemical” vs. “physical” explanations of the radical phenomenon. The first account of unpaired electrons in radicals and their paramagnetic properties was published by Gilbert Lewis (1923).

  40. 40.

    Cf. Paneth and Lautsch 1930.

  41. 41.

    I apply the terminology of Bas van Fraassen here. According to the latter, the expression “observable” refers to unaided acts of perception only and is object-related (e.g., van Fraassen 2001). Hence, and contrasting for example Hacking 1981, the use of even the smallest lens or optical microscope yields representations.

  42. 42.

    Cf. Heidelberger 1998, 2003.

  43. 43.

    Meyer and Rimbach (1921): “Die Chemie ist die Wissenschaft vom Stoffe und seinen Änderungen.”

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Acknowledgements

Parts of this study were presented at different international meetings on the history and philosophy of chemistry in Coburg, Berlin, Philadelphia, and Uppsala over the last few years. I gratefully acknowledge invitations to Berlin (Max-Planck-Institute for the History of Science) and Philadelphia (Chemical Heritage Foundation) and all pertinent comments, particularly those of Carsten Reinhardt (Philadelphia) and Ursula Klein (Berlin). Special thanks go to Jaap van Brakel (Leuven) for his comments on an earlier version of the present text. I am very grateful to Barney Craven (Coburg) for amending grammar and style of the manuscript.

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  1. Faculty of Science and Centre for Science and Culture, Coburg University of Applied Sciences and Arts, Coburg, Germany

    Klaus Ruthenberg

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  1. Department of Chemistry and Biochemistry, University of California, Los Angeles, California, USA

    Eric Scerri

  2. Center for Philosophy and History of Science, Boston University, Boston, Massachusetts, USA

    Lee McIntyre

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Ruthenberg, K. (2015). Radicals, Reactions, Realism. In: Scerri, E., McIntyre, L. (eds) Philosophy of Chemistry. Boston Studies in the Philosophy and History of Science, vol 306. Springer, Dordrecht. https://doi.org/10.1007/978-94-017-9364-3_12

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