1. Chem 125 Lecture 25 10/31/05 Projected material This material is for the exclusive use of Chem 125 students at Yale and may not be copied or distributed further. It is not readily understood without reference to notes from the lecture.

2. Genealogy Top

3. 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

4. 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.

5. 1858 Tetravalence and Self-Linking of Carbon

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

8. "Structural" Formulae

9. CH 3 CH 2 -OH CH 3 -OH

10. Ethyl Ether... CH 3 CH 2 -O-CH 2 CH 3

11. Couper C  12

12. Glycerine CH(OH) 2 CH 2 OH CH 2 CH(OH) 2 CO 2 H CH 2 2 OH OH 2 OH OH

13. English Glucose CH 2 OH CHOH CH(OH) 2 O + H 2 O (HOMO/LUMO Addition Mechanism?)

14. 2 OH English Glucose CH 2 OH CHOH CH (Typo: Addition of H 2, not H 2 O)

15. Kekulé age 13

16. Kekulé age 18 Giessen for architeture

17. 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 know the life of a great city, but there you will not learn chemistry!

18. Kekulé in Heidelberg (1856-58) Performed Research on (CH 3 ) 3 As (Prof. Bunsen's cacodyl radical) in his apartment's kitchen! 1857 - Proposed a new type "Marsh Gas" HHHHHHHH C 1858 - Proposed self-linking of Carbon

19. 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."

20. Ghent (1865) Structure of Benzene Kekulé

21. Bonn (1872) Kekulé

22. Nomenclature Facts, Ideas, and Words  Notation  Models

23. Hofmann's Systematic Hydrocarbon Nomenclature for Radicals (1866) Quartane, (C 4 H 10 )° Quartyl (C 4 H 9 )' Quartene, (C 4 H 8 )'' Quartenyl, (C 4 H 7 )''' Quartine, (C 4 H 6 )iv Quartinyl, (C 4 H 5 )v Quartone, (C 4 H 4 )vi Quartonyl, (C 4 H 3 )vii Quartune, (C 4 H 2 )viii Quartunyl, (C 4 H) ix

24. 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."

25. What SHOULD a Formula Show? Constitution: Nature & Sequence of Bonds Composition: Elements & number of Atoms Isomers

26. Lohschmidt Acetic Acid (1861)

27. Crum-Brown (1861-1866)

28. Kekulé's "Preferable" Notation (1865) Isomers?

29. Molecular Models

30. 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.

31. James Dewar's Brass 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 years later, and called "Dewar Benzene" 4-center bond?

32. Hofmann Croquet-Ball Models (1865)

34. Cl O O _ etc. good O donors _

35. Hofmann Croquet-Ball Models (1865) Isomer? No; Models Show Nature & Sequence Not Position Substitutions

36. Hofmann Croquet-Ball Models (1865) Reactivity! Unfinished or Non-Saturated Cl 2 addition not substitution

37. 3 Acetone  Mesitylene (Kekulé, 1867) Dewar had sent Kekulé brass-strip models in 1866. -H 2 O

38. Genealogy Top

39. End of Lecture 25