1. Chemistry 250-02 Organic Chemistry I Fall, 2014 Day 32 Chapter 11
Organic Chemistry I
Fall, 2014
Day 32
Chapter 11
Substitution and Elimination
Chem Act 13 C & D (Today) then 14 A & B (Wed)

2. McMurry Problem 11.26 A “Walden” cycle
What is the purpose for making B ? Why is [α]D for B positive ? What kind of reaction is B -> C and what is the mechanism ? What is the optical purity of C and what are the %’s of the two enantiomers of C ?
How could you make C from B with 100 % enantiomeric excess (i.e. optically pure) ? What kind of reaction is D -> E and what is the mechanism ? How can you convert A into CH3-CHCl-CH2 -Phenyl ?

3. SN2 It’s not always straight inversion. R. Wester, M. Weidem-ller (U
SN2 It’s not always straight inversion ! R. Wester, M. Weidem-ller (U. Freiburg), W. Hase (Texas Tech) Science 2008, 319, 183

4. Chem Activity 14A Elimination as the reverse of addition

5. An Elimination Reaction

6. Two-Step Elimination (E1)
Carbocation intermediate formed (r.d.s.)
Rate = k [RX] 1 Unimolecular
Unimolecular elimination = E1
Must have β-hydrogen available
Weak “patient” base
Regiochemistry: Zaitsev’s rule
Stereochemistry: E/Z alkenes formed (slight preference for E)

7. SN1 vs. E1

9. Chem Activity 14B

10. One-Step Elimination (E2)
Rate = k [RX]1 [Base]1 Bimolecular
Bimolecular elimination = E2
Must have β-hydrogen available
Strong “impatient” base (RO-, R2N-)
Regiochemistry:
Zaitsev product with small base
Hofmann product with large base
Stereochemistry: anti elimination (usually)

11. The E2 Elimination Reaction

12. E2 Eliminations

13. What are the products ?

14. What are the products ? E1 K+ E2

15. SN1 SN2 E1 E2 or E2cB ? What other products are possible ?

16. SN2 vs. E2

17. What is the product and why ?

18. What is the product and why ?

19. What is the product? Points to consider: What kind of substrate?
Do temperature conditions favor E vs. S?
Good or poor nucleophile?
Strong or weak base?
Big or small base?

20. Hint: you’ve seen this behavior from carbocations before…
What happened here?
Hint: you’ve seen this behavior from carbocations before…

21. Assess the possibilities
Points to consider:
What kind of substrate?
Do temperature conditions favor E vs. S?
Good or poor nucleophile?
Strong or weak base?
Big or small base?

22. Summary

23. Chem Activity 14C E2 via anti periplanar conformer

24. E2 via Anti Stereochemistry

25. Which compound would serve as the best starting material for the transformation shown below?1. 2. 3. 4. 5.

26. Including stereoisomers, how many products are possible from the following reaction?1 2 3 4 5

27. What is the major elimination product?B C D

28. What is the major elimination product?B C D

29. What is the major elimination product? Hint: Memorization Task 14.4B C D

30. What is the major product of the following reaction?1. 2. 3. 4. 5.

31. What is the best base for this reaction?
NaOH
NaOCH3
NaOCH2CH3 Na

32. E1 and E2 Eliminations

33. What is the most likely mechanism for this reaction?
SN1
SN2 E1 E2

34. CA 14C Stereochemistry of E2
Read Model 8 and answer CTQ 36.

35. T/F: Configurational stereoisomers can interconvert via a chair flip.
True; a chair flip converts cis to trans.
True; a chair flip converts axial to equatorial but not tBu.
False; a chair flip does not convert cis to trans.
False; configurational stereoisomers are constitutional isomers.

36. CA 14C Stereochemistry of E2
Read Model 9 and answer CTQ
Note: Pg. 215, CTQ 45 the last product has an –OCH3 group, not –OH.

37. Explain this result

39. What product is formed? A B C

41. What is the most likely product of the following reaction?1. 2. 3. 4. 5.

42. What mechanism is most likely to operate for the following reaction?
SN1
SN2 E1 E2
E1cB

43. Chem Act 14 Table page 220 Favored Mech. Base/Nuc R-X
Rate dependent on [??]
Solvent
Temp
SN1
SN2 E1 E2