Chemistry Reference
In-Depth Information
12.5 The Existence of Radicals as Problem
of Scientific Realism
As to the central statement of
scientific realism
Bas van Fraassen cites Wilfrid
Sellars as follows: “To have good reason to accept a theory is to have good reason to
believe that the entities it postulates are real.”
32
Existence criteria might be formu-
lated scientifically like the Latvian-German chemist and historian of chemistry
(and former student of Ostwald) Paul Walden (1863-1957) communicated in his
monograph on radicals from
1924
. He differentiated three possible cases:
1. radicals are
preparable
chemical
individuals [
isolierbare Individuen
] bearing all
properties of
free and stable molecules [
freier und best
€
andiger Molekeln
], or,
contrasting this,
2. radicals are
not preparable
, but occur intermediary as unsaturated fragments of mole-
cules which react with each other in order to come together immediately to build more
stable chemical entities as end products, or
3. radicals do exist in our imagination only but not as stuff kinds [
Stoffarten
]; mentally we
consider them to be aids in the interpretation of chemical reactions.
33
Hence, according to Walden, the radical concept in chemistry has a continuous
history: he used the same term, be it in a theoretical sense or in an empirical context.
The bridging idea is obviously that of something unsaturated in the sense organic
chemists gave this property at least since the nineteenth century. This “unsaturated
something” is imagined as a structural or substantial entity which is part of a
(or several) more stable structure(s) or substance(s). Intriguingly, Walden described
Gomberg
s triphenylmethyl as a radical of the first kind, although he discussed all
the “classical” problems addressed in the present study in detail. In fact, the free
radical triphenylmethyl (which is the reference of the structure shown in Fig.
12.1
)
cannot be prepared. Rather it exists in solution only where it carries some stabiliz-
ing ligands.
As we have already seen, Gomberg as well considered his radical to be an
existing, real entity that is he believed that he had found an example of a trivalent
carbon compound.
34
A very useful threefold scheme for the taxonomy of scientific theories and
entities from a realist point of view has been proposed by Rom Harr
´
.
35
According
to Harr
´
,
type 1 theories
are cognitive objects with pragmatic properties which refer
to observable entities like snooker balls, the planet Mars, mammal livers,
type
'
32
van Fraassen
1984
, 250.
33
Walden
1924
,3
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
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.” (Harr´
1986
, 70)
