Figure 4.2

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 • 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 -32 oC 78oC 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· Chlorination – early TS looks less like radical Bromination – late TS looks a lot like radical