1. Competition among SN2, SN1, E2, and E1 Reactions

2. Competition among SN2, SN1, E2, and E1 Reactions

3. Rate-Determining Steps Revisited
SN2
SN1 E2 E1

4. Nucleophile Strength

5. The Free Energy Diagram

6. Hammond Postulate

7. Hammond Postulate Applied to SN2 Reactions

8. Nucleophile Strength Revisited

9. Effective Electronegativity

10. The Base Strength in E2 and E1 Reactions

11. The Base Strength in E2 and E1 Reactions

12. Steric Hindrance in SN2 Reactions

13. Concentration of the Attacking Species

14. Leaving Group and pKa

15. Leaving Groups and SN2 Rates

16. Leaving Groups and SN1 Rates

17. Leaving Group Ability and SN2/SN1/E2/E1 Reactions
SN1 reactions are more sensitive to leaving group ability than SN2 reactions are.
Excellent leaving groups favor SN1 and E1 reactions over corresponding SN2 and E2 reactions.

18. SN2 Reactions and the Hybridization

19. Effect of Alkyl Groups on the C Bonded to the L

20. Rate of SN2 and Steric Hindrance

21. E2 and Steric Hindrance

22. Rate of SN1 and E1 versus Carbocation Stability

23. Hyperconjugation secondary can do 2x, tertiary can do 3x
The increased stability of a carbocation as methyl or other groups are added to the C+ is due to hyperconjugation. Conjugation: p orbitals overlap. Hyperconjugation: sigma MO overlaps with p orbital. Coplanar but not parallel, so overlap not as good, stabilization not as much as normal conjugation.
secondary can do 2x, tertiary can do 3x

24. Summary of the Influence of the Number of Alkyl Groups on the Carbon

25. Solvent Effects

26. Solvation

27. Solvent Effects
TAB09.10_Karty1_CH09

28. polar solvents especially good for SN1 (OK for some SN2)
We’ve already seen that H-bonding to a nucleophile makes it less reactive. So nucleophiles are more reactive in solvents that cannot H-bond.
aprotic solvents
(no H on O or N)
cannot H-bond to Nu
especially good for SN2

29. So let’s summarize everything.

32. Leaving Group Ability

33. Regioselectivity in Elimination Reactions: Zaitsev’s Rule

34. Another Example of Zaitsev’s Rule

35. Exception to Zaitsev’s Rule

36. Inter- vs Intra- molecular Reaction

37. Inter- vs Intra- molecular Reaction
3 very close, entropy overcomes ring strain
4, not as close, ring strain overcomes entropy
5 and 6, not much strain so entropy helps
7 not as good, but OK
larger rings, entropy not much help
forms ring