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Chemistry 125: Lecture 22
Radical and Type Theories
(1832-1850)
Work by Wöhler and Liebig on benzaldehyde inspired a general theory of organic chemistry focusing
on so-called “radicals”, collections of atoms that appeared to behave as elements and to persist
unchanged through organic reactions. Liebig’s French rival, Dumas, temporarily advocated radicals, but
converted to the competing theory of “types”, which could accommodate substitution reactions. These
decades teach more about the psychology, sociology, and short-sightedness of leading chemists than
about fundamental chemistry, but both discredited theories survive in competing schemes of modern
organic nomenclature. The HOMO-LUMO mechanism of addition to alkenes and the SOMO mechanism
of free-radical chain reactions are introduced.
Synchronize when the speaker finishes saying
“…went to work for most of a month with Liebig...”
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1832
Radical Theory
Oil of
Bitter
Almonds
Persistence
of
C7H
Toward
Structure
With
Analysis?
5O
So?
Organic Dualism  Benzoyl Radical
O2
C7H6O
Bz • H
Cl2
Br2
C7H6O2
Bz • OH
Oil of
CBitter
7H5OCl
Bz • Cl
Almonds
KI
NH3
PbS
C7H5OI
Bz • I
C7H7ON
Bz • NH2
A radical can
C14H10O2S
C7H5OBr
be the “base”
Bz2 • S
Bz • Br
of more than
just an acid! Liebig & Wöhler (1832)
During the 1830s compound
radicals were discovered
everywhere:
Liebig: Acetyl
Bunsen:
Piria:
Dumas:
Ethyl (Berzelius)
Cacodyl (Me2As •)
Salicyl
Methyl
Cinnamyl
Cetyl
Ethylene
Dualistic Radical Theory
Survives
in our Nomenclature
Two Words (+ and -)
e.g. Ethyl Chloride
-yl
ether
from
ulh
(wood , matter)
from aiqo (to shine) 1700s

hence ethyl
sky
(Liebig, 1834)

colorless liquid
meth-yl
-ene
from
from
mequ (wine, spirit)
ulh (wood, matter)
from
Greek Feminine
-hnh Patronymic
"daughter of"
hence methylene
(Dumas, 1835)
"Daughter of wood spirits"
CH3OH = CH2 + H2O
(1840)
(1852)
CH3 methyl from methylene
ethylene : ethyl :: methylene : methyl
C2H4 : C2H5 :: CH2 : CH3
C3
C4
From C3 Propionic Acid (1847)
C3H7 Propyl
C3H6 Prop(yl)ene pro (protos first) pin (pion fat)
Derivatives of acids with >C2 were like fats,
unlike C1 (formic) and C2 (acetic)
C4H9 Butyl
C4H8 But(yl)ene
From C4 Butyric Acid (1826)
Lat. butyrum (butter)
from rancid butter
Jean-Baptiste
André
Dumas
(7/14/1800-1884)
Post-Napoleonic
Guardian of
French Chemistry
http://clendening.kumc.edu
Chaired Professor:
Sorbonne 1841École Polytechnique 1835École de Médicine 1839Persistent Opponent
of Liebig and
Berzelius
Note on the Present State of Organic Chemistry
by MM. Dumas and Liebig
(1837)
Sixty years have hardly passed since the ever
memorable time when this same assembly heard the
first discussions of the fertile chemical doctrine which
we owe to the genius of Lavoisier. This short span of
time has sufficed to examine fully the most delicate
questions of inorganic chemistry, and anyone can easily
convince himself that this branch of our knowledge
possesses almost everything that it can with the methods
of observation available.
MYOPIA!
…there barely remain a few cracks here and there
(cf. Lavoisier, “in our own time”)
to fill in.
Note on the Present State of Organic Chemistry
by MM. Dumas and Liebig
(1837)
In a word, how with the help of the laws of inorganic
chemistry can one explain and classify such varied substances as one obtains from organic bodies,
and which nearly always are formed only
of carbon, hydrogen, and oxygen, to which
elements nitrogen is sometimes joined?
printartist
This was the great and beautiful question
of natural philosophy,
Note on the Present State of Organic Chemistry
by MM. Dumas and Liebig
(1837)
a question well designed to excite the highest degree of
competition among chemists; for once resolved the most
beautiful triumphs were promised to science. The
mysteries of plants, the mysteries of animal life would be
unveiled before our eyes; we would seize the key to all
the changes of matter, so sudden, so swift, so singular,
that occur in animals and plants; more importantly we
would find the means of duplicating them in our
laboratories.
Note on the Present State of Organic Chemistry
by MM. Dumas and Liebig
(1837)
Well, we are not afraid to say it, and it is not an assertion which we make lightly: this great and beautiful question is today answered; it only remains to follow through
on all the consequences which its solution entails...
In fact to produce with three or four elements such
varied combinations, more varied perhaps than those
which make up the whole inorganic kingdom, nature has
chosen a path as simple as it was unexpected; for with
elements she has made compounds which behave in all
their properties like elements themselves.
And this, we are convinced, is the entire secret of
organic chemistry.
Note on the Present State of Organic Chemistry
by MM. Dumas and Liebig
(1837)
Thus organic chemistry possesses its own elements,
which sometimes play the role of chlorine or oxygen in
inorganic chemistry and sometimes, on the contrary, play
the role +
of metals. Cyanogen, amide, benzoyl, the radicals
of ammonia, of aliphatics, of alcohol, and analogous
substances, these are the true elements with which organic
chemistry operates…
To discover these radicals, to study them, to characterize
them, this has been our daily study for ten years.
Note on the Present State of Organic Chemistry
by MM. Dumas and Liebig (1837)
Sometimes, none the less, our opinions have appeared
to differ, and then, with each of us drawn on by the heat
of our battle with nature, there arose between us
discussions whose liveliness we both regret.
Actually when we were able to discuss questions which
separated us in several friendly meetings, we soon
realized that we were in agreement on the principles...
We then understood that united we could undertake a
task before which either of us in isolation would have
recoiled…
We will analyze every organic substance…to establish
reliably what sort of radical it refers to…
Note on the Present State of Organic Chemistry
by MM. Dumas and Liebig (1837)
Each of us has, in fact, opened his laboratory to all
young men who were motivated by true love of science;
they have seen all, understood all. We have worked under
their eyes, and have had them work under ours, in such a
way that we are surrounded by young rivals, who are the
hope of science, and whose work will be added to ours
and mingle with ours, for it will have been conceived in
the same spirit and carried out by the same methods…
This is not an effort conceived for personal gain or in the
interest of narrow vanity. No, and in a collaboration
which is perhaps unheard of in the history of science, this
is an undertaking in which we hope to interest every
(unimaginative megalomania)
chemist in Europe.
The electronic character of radicals was
Trouble in Paradise
troublesome for Coulombic dualism.
e.g. preparation of benzoyl chloride
C7H5O • H + Cl = C7H5O • Cl + H • Cl
+
+
+
- + -
?
1840s - 1850s
Substitution
or Type or Unitary
Theory
Tuileries
cough!
Musée d'Orsay (www.histoire-image.org)
choke!
Violently irritating
fumes from wax
candles spoil soirée
at the Tuileries
Palace (~1830)
Dumas identifies
the culprit as HCl
from wax that had
been bleached
by Cl2.
 organic
compounds can
"fix" chlorine gas!
Bal costumé au Palais des Tuileries. 1867
Two ways wax could "fix" chlorine:
HOMO / LUMO
*
Cl
p
CH2
“olefiant gas”
Cl CH2
CH2
+ ••
Cl
*+
••
CH2
••
Cl
CH2
Cl
CH2 Cl
“oil of Dutch
(actually
both
once)
(1795)
Addition
ofsteps
Cl2 toatan
Alkenechemists”
(HOMO/LUMO)
HOMO
LUMO
HOMO
LUMO
n
Cl
Two ways wax could "fix" chlorine:
Cl
Cl
single-electrons

single-barbed
arrows SOMO
•
Cl
CH2
CH2
Cl CH2
CH2
+
Cl
CH2
Cl
CH2 Cl
Addition of Cl2 to an Alkene (HOMO/LUMO)
•
"free-radical chain"
lots of product from one initial photolysis
Cl H CH3
•
CH3 Cl Cl
•
Cl
weak bond No
“make-as“make-ashigh HOMO!
Use light to promote an electron to *Cl-Cl
(58 kcal/mole) you-break”
you-break”
H Cl
Still hard to break!
CH3Cl
Free-Radical Substitution of Cl • for H • (SOMO)
1830s - 1850s
“Substitution”
or “Type”
or “Unitary”
Theory
More Trouble for Radicals - Dumas (1839)
Photochlorination of acetic acid
transmuted the acetyl "element".
C2H3O • OH + Cl = C2H2ClO • OH + H • Cl
Similar Acids!
C2HCl2O • OH
C2Cl3O • OH
Hydrogen may be substituted by an
equivalent amount of halogen, oxygen, etc.
without changing molecular type.
Four Types Recognized by 1853
O
O
H
H
H
H
Cl
H
C2H5
C2H5
K
H
+
I
= O
C2H5
+ KI
C2H5
Williamson Ether Synthesis (1850)
H
N H
H
C2H5
N C
H2H5
C
H2H5
Unitary (not Dualistic) Theory
[Molecules are like] planetary systems held together
by a force resembling gravitation, but acting in accord
with much more complicated laws.
Dumas (1840)
Formulae…may be used as an actual image of
what we rationally suppose to be the arrangement of
constituent atoms in a compound, as a orrery is an
image of what we conclude to be the arrangement of
our planetary system. A. W. Williamson (age 27, 1851)
Butyl_Bromide
Bromobutane
Two-Word Relic
One-Word Relic
of Radical
Dualism
Theory
A Philosopher
lecturing
on the Orrery of "Unitary"
Joseph Wright of Derby (1766)
Berzelius (1838)
“By reacting chlorine with ordinary ether [Dumas] produced a very interesting compound which he reckoned,
according to the theory of substitutions, to be an ether in
which 4 atoms of chlorine replace 4 atoms of hydrogen.
An element as eminently electronegative as chlorine
would never be able to enter into an organic radical :
this idea is contrary to the first principles of chemistry…”
A neutral anhydrous tartrate loses an atom of water at
+190°; it has ceased to be a tartrate and has become
another salt
first use of “R” to denote a generalized radical
On the Reaction of Chlorine
Remarks
onofthe
Previous Paper
On
thethe
Law
Substitutions
and
with
Chlorides
of Ethanol
Theory of
andthe
Methanol
andTypes.*
Several
Points of the Ether Theory.
amLaw
a farofcry
from sharingand
OnIthe
Substitutions
the
thatof
M.Types.
Dumas
theideas
Theory
has linked to the
so-called laws of
the substitution theory.
“Liebig’s
Annalen”
Can one substitute the elements
that play their role in any
simple or compound substance
equivalent for equivalent ?
On the YES!
Substitution Law
Justus Liebig
of M. Dumas.
1840
*) Letter to J.L.
On the Substitution Law and the Theory of Types
(letter to Justus Liebig)
Paris, 1 March 1840
Monsieur!
I am eager to communicate to you one of the most
striking facts of organic chemistry. I have confirmed
the substitution theory in an extremely remarkable and
completely unexpected manner. Only now can one
appreciate the great value of this theory and foresee the
immense discoveries that it promises to reveal.
manganese acetate [MnO + C4H6O3]
[MnCl2 + C4Cl6O3]
[MnO + C4Cl6O3]
[Cl2Cl2 + C4Cl6O3]
[Cl2Cl2 + Cl8Cl6Cl6]
On the Substitution Law and the Theory of Types
(letter to Justus Liebig)
For all I know, in the decolorizing action of chlorine,
hydrogen is replaced by chlorine, and the cloth, which is
now being bleached in England, preserves its type according to the substitution laws.** I believe, however, that
atom-for-atom substitution of carbon by chlorine is my
own discovery. I hope you will take note of this in your
journal and be assured of my sincerest regards, etc.
S. C. H. Windler
* I have just learned that there is already in the London shops
a cloth of chlorine thread, which is very much sought after and
preferred above all others for night caps, underwear, etc.
In 1849 Kolbe Prepared
Free Methyl Radical
(electrolysis)
CH3 • CO2H
CH3 + CO2 + H
but molecular weight would show
he had its dimer H3C-CH3
(Cannizzaro, 1860)
Ironically the key reactions of both radical
and type theories did involve free radicals
(SOMO not HOMO/LUMO)
O
C
C
•
H
O
H3 C
C
OH
O
H3 C
C
O
O2
O-
O
C
OH
O
O
Cl
2
•
H2 C C
Cl CH2 C
OH
OH
-e• CH3
CH3 CH3
End of Lecture 22
Oct. 27, 2008
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