Carey Chapter 4 – Alcohols and Alkyl Halides Figure 4.2

4.1 Functional groups – a look ahead

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

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

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

4.5 Bonding in alcohols and alkyl halides Figure 4.1

4.5 Bonding in alcohols and alkyl halides Figure 4.2

4.6 Physical properties – intermolecular forces CH3CH2CH3 CH3CH2F CH3CH2OH propane fluoroethane ethanol b.p. -42oC -32 oC 78oC

4.6 Physical properties – intermolecular forces Figure 4.4

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

4.7 Preparation of alkyl halides from alcohols and HX

4.8 Mechanism of alkyl halide formation

4.8 Energetic description of mechanism – Step 1 : protonation Figure 4.6

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

4.8 Energetic description of mechanism – Step 3 : trapping carbocation Figure 4.9

4.9 Full mechanism “pushing” curved arrows

4.9 Full SN1 mechanism showing energy changes Figure 4.11

4.10 Carbocation structure and stability Figure 4.8 Figure 4.15 Hyperconjugation

4.10 Relative carbocation stability Figure 4.12

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:

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

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

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)

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

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

4.15 Free Radical Chlorination of Methane

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

4.16 Bond Dissociation Energies (BDE)

4.17 Mechanism of Methane Chlorination

4.17 Mechanism for Free Radical Chlorination of Methane

4.18 Free Radical Halogenation of Higher Alkanes

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 radical, formed faster

4.18 Free Radical Halogenation of Higher Alkanes Figure 4.16

4.18 Bromine radical is more selective than chlorine radical Consider propagation steps – endothermic with Br·, exothermic with Cl·

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