Chem 125 Lecture 2510/31/05

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Genealogy Top

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

"Structural"Formulae

CH3CH2-OH

CH3-OH

Ethyl Ether

...

CH3CH2-O-CH2CH3

Couper C 12

Glycerine

CH(OH)2

CH2OH

CH2

CH(OH)2

CO2H

CH2

2OH

OH

2OH

OH

English GlucoseCH2OH

CHOH

CHOH

CHOH

CHOH

CH(OH)2O + H2O(HOMO/LUMO Addition Mechanism?)

2OH

English GlucoseCH2OH

CHOH

CHOH

CHOH

CHOH

CH(Typo: Addition of H2, not H2O)

Kekulé age 13

Kekulé age 18 Giessen for architeture

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)3As(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

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

Kekulé on Notation("Benzene" Paper, 1865)

"For greater clarity I am presenting at the end of this note a table giving graphical formulae for most of the substances mentioned. The idea that these formulae are designed to express is rather well known now; so it will not be necessary to dwell upon it. I am keeping the form that I had adopted in 1859 when expressing for the first time my views on the atomic constitution of molecules. This form is nearly identical with that which M. Wurtz used in his beautiful lectures on chemical philosophy. It seems to me preferable to the modifications proposed by MM. Loschmidt and Crum-Brown."

What SHOULDa Formula Show?

Constitution:Nature & Sequence of Bonds

Composition:Elements & number of Atoms

Isomers

Lohschmidt Acetic Acid (1861)

Crum-Brown (1861-1866)

Kekulé's "Preferable" Notation (1865)

Isomers?

MolecularModels

Gaines Models Now, if a class thus instructed be at the recitation bench, and one of them is requested to form carbonic acid, he will walk quickly to the table in front, where the box is open, and place on one of the shelves a cube marked 6, and two marked 8 – carbon, one, and oxygen, two. If requested to form lime, he will place on the shelf a cube marked 20, (calcium,) and another marked 8, (oxygen,) these being the elements of lime. These cubes being all placed in contact, and the pupil being asked, “What have we now?” answers, “Carbonate of lime.”

Another pupil may then be asked to give the proximate analysis for carbonate of lime, and the cubes before him will indicate the answer and fix it in his memory: “It is composed of one equivalent of carbonic acid, (22) and one of lime, (28).” Another may be requested to give the ultimate analysis, and by the same means he is furnished with the answer: “Carbonic acid is composed of one atom of carbon and two of oxygen, and the lime is composed of one atom of calcium and one of oxygen.”

The intelligent educator will see at a glance, that in this chemical alphabet he has the means of at once arresting the attention of his class, and converting what has hitherto been an irksome task into a pleasant recreation. The atomic theory, the characteristics of affinity, the law of multiple proportions, the nomenclature, isomerism, &c., may all be learned in half the time required heretofore, and learned so as not likely ever to be forgotten.

James Dewar'sBrass Strip

Models(1866)

"to make the combination look like an atom, a thin round disc

of blackened brass can be placed under the central nut"

Prepared ~100 yearslater, and called

"Dewar Benzene"

4-center bond?

Hofmann Croquet-Ball Models (1865)

Hofmann Croquet-Ball Models (1865)

Hofmann Croquet-Ball Models (1865)

Cl• •

• •

• ••

•

• •

• •

• •

O• •

• •

• •O

_

etc.good O donors

_

Hofmann Croquet-Ball Models (1865)

Isomer?

No; Models ShowNature & Sequence

Not Position

Substitutions

Hofmann Croquet-Ball Models (1865)Reactivity!

Unfinished orNon-Saturated

Cl2

additionnot

substitution

3 Acetone Mesitylene (Kekulé, 1867)

Dewar had sent Kekulé brass-strip models in 1866.

-H2O

Genealogy Top

End of Lecture 25