1. Carey Chapter 4 – Alcohols and Alkyl Halides
Figure 4.2

2. 4.1 Functional groups – a look ahead

3. 4.2 IUPAC nomenclature of alkyl halides 2-chloro-5-methylheptane
Functional class nomenclature
pentyl chloride
cyclohexyl bromide
1-methylethyl iodide
Substitutive nomenclature
2-bromopentane
3-iodopropane
2-chloro-5-methylheptane

4. 4.3 IUPAC nomenclature of alcohols
2-propanol
1-pentanol
cyclohexanol
2-pentanol
1-methyl cyclohexanol
5-methyl-
2-heptanol

5. 4.4 Classes of alcohols and alkyl halides
Primary (1o)
Secondary (2o)
Tertiary (3o)

6. 4.5 Bonding in alcohols and alkyl halides
Figure 4.1

7. 4.5 Bonding in alcohols and alkyl halides
Figure 4.2

8. 4.6 Physical properties – intermolecular forces
CH3CH2CH3 CH3CH2F CH3CH2OH
propane fluoroethane ethanol
b.p. -42oC oC oC
Figure 4.4

9. 4.6 Physical properties – water solubility
alcohols
Figure 4.5
Alkyl halides are generally insoluble in water (useful)

10. 4.7 Preparation of alkyl halides from alcohols and HX

11. 4.8 Mechanism of alkyl halide formation

12. 4.8 Energetic description of mechanism
Step 1 - protonation
Figure 4.6

13. 4.8 Energetic description of mechanism
Step 2 – carbocation formation
Figure 4.7

14. 4.8 Energetic description of mechanism
Step 3 – trapping the carbocation
Figure 4.9

15. 4.9 Full mechanism “pushing” curved arrows

16. 4.9 Full SN1 mechanism showing energy changes
Figure 4.11

17. 4.10 Carbocation structure and stability
Figure 4.8
Figure 4.15
Hyperconjugation

18. 4.10 Relative carbocation stability
Figure 4.12

19. 4.11 Relative rates of reaction of R3COH with HX
Relative Rates of Reaction for Different Alcohols with HX
Related to the stability of the intermediate carbocation:

20. 4.11 Relative rates of reaction of R3COH with HX
Figure 4.16
Rate-determining step involves formation of carbocation

21. 4.12 Reaction of methyl and 1o alcohols with HX – SN2

22. 4.12 Substitution Reaction Mechanism - SN2
Transition state
Alternative pathway for alcohols that cannot form a good carbocation
Rate determining step is bimolecular (therefore SN2)
Reaction profile is a smooth, continuous curve (concerted)

23. 4.13 Other methods for converting ROH to RX
Convenient way to halogenate a 1o or 2o alcohol
Avoids use of strong acids such as HCl or HBr
Usually via SN2 mechanism

24. 4.14 Free Radical Halogenation of Alkanes
R-H + X2 R-X + H-X
Types of bond cleavage:
heterolytic
homolytic

25. 4.15 Free Radical Chlorination of Methane

26. 4.16 Structure and stability of Free Radicals
Orbital hybridization models of bonding in methyl radical (Figure 4.17)

27. 4.16 Bond Dissociation Energies (BDE)

28. 4.17 Mechanism of Methane Chlorination

29. 4.17 Mechanism for Free Radical Chlorination of Methane

30. 4.18 Free Radical Halogenation of Higher Alkanes
Radical abstraction of H is selective since the stability of the ensuing radical is reflected in the transition state achieved during abstraction.
Lower energy, formed faster

31. 4.18 Free Radical Halogenation of Higher Alkanes
Figure 4.16

32. 4.18 Bromine radical is more selective than chlorine
Consider propagation steps – endothermic with Br·, exothermic with Cl·
Bromination – late TS looks a lot like radical
Chlorination – early TS looks less like radical