Radicals, Reactions, Realism - Philosophy of Chemistry - page 190

main aim in the first place was just to synthesize a new compound, and then to find
evidence for trivalency rather than to find a stable radical and establish the revised
radical theory, at least one thing had become common knowledge in chemistry:
there are radicals out there, which in certain aspects, e.g. structurally, fit to the old
hypotheses, and some of them can even be characterized empirically. About
20 years later theoretical chemists invented their version of radical theory which
was alien to the former versions of the nineteenth century (but not entirely incom-
patible) as it were 38 : a quantum mechanical description of electron configurations
comprising unpaired, “anti-bonding” (“radical”) electrons. 39

12.6 Radicals as Public Hallucinations: The Role
of Experimentation

So to speak, the triphenylmethyl radical and, for comparison, the methyl radical 40
are situated at the opposite ends of a virtual scale from empirical to theoretical
substances or observable to unobservable chemical species 41 : methyl can only be
subjected to experiments if very specific conditions are set by the instrumentation,
whereas triphenylmethyl (and its relatives) in principle can be studied by classical
means (e.g., “wet chemistry”) and - at least in principle - by using unaided human
senses. To find out more about the epistemological status of the radical concept it is
therefore necessary to analyze the particular experimental situation.
Michael Heidelberger suggests a taxonomy of roles of (instrumental) experi-
mentation. 42 According to this functional taxonomy, there are two basic types of
experiments, those to improve or expand knowledge and those to adjust actual
knowledge to a theoretical context. The first type can be differentiated into a
productive, a representative, and a constructive or imitative function. Productive
is an experimental setting that produces phenomena which usually could not

38 The radical concept has run through several significant changes (for discussions of the nine-
teenth century developments see Gomberg 1932 ; Gay 1976 ; Rocke 1984 ). Therefore it is ques-
tionable 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

Early theoretical works in the twentieth century are Pauling and Wheland 1933 ;H ¨ ckel 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

Cf. Paneth and Lautsch 1930 .
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 Cf. Heidelberger 1998 , 2003 .