Chemistry Reference
In-Depth Information
break of the quadrivalence doctrine was the main criterion for a substance to be
classified as a radical. Consistently, he used the notion “radical” right from the start
of his investigations.
11
Although Gomberg not only failed to synthesize the desired entity, and although
he initially characterized the found products incorrectly and incompletely - the
substance he found was actually the dimeric peroxide
12
of triphenylmethyl -
he eventually found his path into a distinguished professional career because he
systematically and steadily kept working in that field which he entered - by chance.
The main concern of his research concept from 1900 on was the proof of the
possible trivalency of carbon atoms rather than to install radical chemistry
(as modern chemistry has it
13
). He even used the careful term “radicle” in his
Gomberg 1901 which was used to address molecular groupings (like “methyl”,
CH
3
, in methylchloride or “methylen”, CH
2
, in methylenchloride), at least if we
follow Ostwald
s
Grundlinien der Anorganischen Chemie
from 1900.
14
“It was
against this background of uninterrupted progress [using the hypothesis of quadri-
valent carbon atoms in synthetic organic chemistry] that for almost half a century a
publication appeared with the startling title ›Triphenylmethyl, an Instance of
Trivalent Carbon‹. The original intention of the experimenter was to prepare a
new substance of the composition (C
6
H
5
)
6
C
2
...
'
”
15
More than 10 years of scientific
argument were necessary before the concept of what was called “free radicals” -
although only very few of them could have been characterized or isolated - was
accepted in the community of organic chemists.
16
As to the main arguments for
this acceptance, Gomberg mentioned particularly two: the “hexaphenylethane
riddle”,
17
that is the problem of the impossibility to prepare this compound, and
the successful synthesis of the trisbiphenylylmethyl radical by Wilhelm Schlenk in
1910.
18
The latter compound showed comparable properties like the Gomberg
“radical” and thus helped to foster the central hypothesis. Finally, Gomberg
claimed the following:
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
The formation of which is reversible (expressed by color changes). (C
6
H
5
)
6
C
O
O
C
(C
6
H
5
)
6
comes to 88.0 % C and 5.8 % H.
13
Gilbert Lewis (1875-1946) seems to have introduced the radical concept of unpaired electrons
and the paramagnetism of such radicals (Lewis
1923
).
14
Note that the original “Radikal” with the description referred to here was translated into
“radicle”, see the 2nd ed. (Ostwald
1904
, 406).
15
Gomberg
1928
, 163. Presumably Gomberg
'
s formulation inspired Ihde when he wrote his
statement cited at the introduction of the present contribution.
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
Cf. the title of McBride
1974
.
18
A surveying account of work and life of Wilhelm Schlenk is given in Tidwell
2001
.
