Chemistry 125: Lecture 22October 26, 2009

Type Theory, Valence Theory & Constitutional Structure (1858)

By mid-century there was serious conflict between the French advocates of type theory

and the Germanic advocates of radical theory. Youthful chemists Couper and Kekulé

replaced both radical and type theories with a new approach involving atomic valence and

molecular structure, and based on the tetravalence and self-linking of carbon. Valence

structures offered the first clear explanation for isomerism, and led to the invention of

nomenclature, notation, and molecular models closely related to those in use today.

For copyright notice see final page of this file

1830s - 1850s

“Substitution”or “Type”

or “Unitary”Theory

C2H3O • OH C2H2ClO • OH

Photochlorination of acetic acid

Cl H • Cl+ = +C2H3O • OH C2H2ClO • OH

More Trouble for Radicals - Dumas (1839)

Hydrogen may be substituted by anequivalent amount of halogen, oxygen, etc.

Similar Acids! C2HCl2O • OH

C2Cl3O • OH

without changing molecular type.

transmuted the acetyl "element".

Four Types Recognized by 1853

H

H

H

Cl

H

HO

H

HN H

C2H5

HO

C2H5

HN H

KC2H5

C2H5

C2H5

I+ =

C2H5

C2H5

O + KI

Williamson Ether Synthesis (1850)

Butyl_BromideTwo-Word Relic

of Radical Dualism

BromobutaneOne-Word Relic

of "Unitary" Theory

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)

A Philosopher lecturing on the Orrery Joseph Wright of Derby (1766)

A neutral anhydrous tartrate loses an atom of water at +190°; it has ceased to be a tartrate and has become another salt

Berzelius (1838)

“By reacting chlorine with ordinary ether [Dumas] pro-duced 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…”

first use of “R” to denote a generalized radical

“Liebig’s Annalen”

I am a far cry from sharing the ideas that M. Dumas

has linked to the so-called laws of

the substitution theory.

1840

On the Reaction of Chlorine with the Chlorides of Ethanol

and Methanol and Several Points of the Ether Theory.

On the Substitution Lawof M. Dumas.

Remarks on the Previous Paper

Can one substitute the elements that play their role in any

simple or compound substance equivalent for equivalent ?

On the Law of Substitutions andthe Theory of Types.

Justus Liebig

*) Letter to J.L.

On the Law of Substitutions andthe Theory of Types.*

YES!

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]

[Cl2Cl2 + Cl8Cl6Cl6]

[MnCl2 + C4Cl6O3]

[Cl2Cl2 + C4Cl6O3]

[MnO + C4Cl6O3]

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 accor-ding 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 showhe had its dimer H3C-CH3

(Cannizzaro, 1860)

CO

HC

O

OH

O2

CO

OHC

O

OH

Cl2H3C CH2Cl

CO

OCH3

-e-

H3C CH3-CH3•

Ironically the key reactions of both radical and type theories did involve free radicals

(SOMO not HOMO/LUMO reactions)

CO

•

CO

OHH2C

•

Genealogy Top

Archibald Scott

Couper(1831-1892)

1851-1856 Dilettante Edinburgh/Berlin

Classics, MetaphysicsLogic, Moral Philosophy,

Concerts

1855 Chemist Berlin

1856 Chemist Paris (Wurtz) - Salicylic Acid

Fired

1859-1892 Mental Invalid

1858

Kirkintilloch

(near Glasgow)

Endrick Waterwhere Couper (age 28) suffered sunstroke

while fishing during recuperation

“Laurel Bank”Kirkintilloch

where his mother cared for him during his final 33 years

Theory and Types

p. 106 - on the French Type Theory

Should the principle which is therein adopted be applied to the common events of life, it will be found that it is simply absurd. Suppose that some one were to systematize the formation of letters into words that formed the contents of a book.

p. 106 - on the French Type Theory

Were he to begin by saying that he had discovered a certain word which would serve as a type, and from which by substitution and double decomposition all the others are to be derived, - that he by this means not only could form new words, but new books, and books almost an infinitum, - he would state certainly an empirical truth.

p. 106 - on the French Type Theory

At the same time, however, his method would, judged by the light of common sense, be an absurdity. But a principle which common sense brands with absurdity, is philosophically false and a scientific blunder.

p. 107 - on the German Radical Theory

I can only remark that it is not merely an unprofitable figure of language, but is injurious to science, inasmuch as it tends to arrest scientific inquiry by adopting the notion that these quasi elements contain some unknown and ultimate power which it is impossible to explain.

p. 107 - on the German Radical Theory

It stifles inquiry at the very point where an explanation is demanded, by putting the seal of elements, of ultimate powers, on bodies which are known to be anything but this.

but stated undiplomatically,especially for a newcomer.

Absolutely true

Science demands the strict adherence to a principle in direct contradiction to this view. That first principle, without which research cannot advance a step, dare not be ignored; namely, that a whole is simply a derivative of its parts.

p. 108 - Look to the Elements

[?]

As a consequence of this, it follows that it is absolutely necessary to scientific unity and research to consider these bodies as entirely derivative, and as containing no secret ultimate power whatever, and that the properties which these so-called quasi elements possess are a direct consequence of the properties of the individual elements of which they are made up.

p. 108 - Look to the Elements

p. 109 - Focus on Carbon In applying this method, I propose at present to consider the single element carbon. This body is found to have two highly distinguishing characteristics: -

1. It combines with equal numbers of hydrogen, chlorine, oxygen, sulfur, &c.

2. It enters into chemical union with itself.

These two properties, in my opinion, explain all that is characteristic of organic chemistry.

1858

Tetravalenceand Self-Linking

of Carbon

C2 as nucleus H = 1 C = 6 O = 8 Cl = 35.5

(Cf. Wöhler/S.C.H.Windler hoax)

"Structural"Formulae

CH3CH2-OH

CH3-OH

Ethyl Ether

...

CH3CH2-O-CH2CH3

There is a Printer’s Error.(This was unfamiliar territory.)

Couper C 12

Glycerine

CH(OH)2

CH2OH

CH2

CH(OH)2

CO2H

CH2

2OH

OH

2OH

OHguessed

a bit wrong

English GlucoseCH2OH

CHOH

CHOH

CHOH

CHOH

CH(OH)2O + H2OTry 2- or 3-step HOMO/LUMO

scheme for H2O + R2C=O

guessedright forhydrate!

2OH

English GlucoseCH2OH

CHOH

CHOH

CHOH

CHOH

CH(Typo: Adds H2, not H2O, to C=O)

French version of same paper.

Lines for C-C Bonds

Old Aisle CemeteryKirkintillochOct. 28, 2008 Special thanks

to our agentSusan Frew

from K. HafnerAngew. Chem. Int. Ed.

18, 641 (1979)

Drawing by Kekulé age 13

By Kekulé age 18 Giessen for architeture

from K. HafnerAngew. Chem. Int. Ed.

18, 641 (1979)

Liebig's advice to Paris-bound graduate August Kekulé (1851)

There you will broaden your horizons,

there you will learn a new language,

there you will learn to knowthe life of a great city,

but there you will not learn chemistry!

Kekulé in Heidelberg (1856-58)

Performed Research on (CH3)2As(Prof. Bunsen's cacodyl radical)

in his apartment's kitchen!

1857 - Proposed a new type, "Marsh Gas"

HHHH

C

1858 - Proposed self-linking of Carbon

(tetravalence)

Kekulé Claims Priority (1858)Observations on Mr. Couper's New Chemical Theory

"In fact, in two memoirs which have appeared in Liebig's Annalen...I have put forward different views, which, in my opinion, should furnish a clearer insight into the constitution of chemical compounds.

I may be allowed to indicate that [my first paper] lays down the principle…which I have called the basicity of atoms [we would say 'valence']. If Mr. Couper thinks he has discovered the cause of this difference of basicity in the existence of a special kind of affinity, I am the first to admit that I have no right to contest his priority in this."

Ghent (1865) Structure of Benzene

Kekulé

Bonn (1872)

Kekulé

Nomenclature

Facts, Ideas, and Words

Notation

Models

Hofmann's

SystematicHydrocarbonNomenclaturefor Radicals

(1866)

Quartane, (C4H10)° Quartyl (C4H9)' Quartene, (C4H8)'' Quartenyl, (C4H7)''' Quartine, (C4H6)iv Quartinyl, (C4H5)v Quartone, (C4H4)vi Quartonyl, (C4H3)vii Quartune, (C4H2)viii Quartunyl, (C4H) ix

End of Lecture 22Oct. 26, 2009

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