Chapter 3. Reactions of Alkenes 3.1. Electrophilic Addition

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Chapter 3. Reactions of Alkenes

• 3.1. Electrophilic Addition reactions on
  carbon-carbon double bonds
• General reaction pattern
• Incorporation of an electrophile by the CC.
  Result a carbocation
• Incorporation of a nucleophile. Result product
  of the addition reaction.

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General reaction pattern (Continued)

• Reaction Orientation follows Markovnikovs Rule
  In an electrophilic addition to an alkene, the
  electrophile adds in such a way as to form the
  most stable intermediate.
• Markovnikov Product formed following
  Markovnikovs rule

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General reaction pattern (Illustration)
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Electrophilic Additions to CC bonds
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Addition of Hydrogen Halides to CC bonds

• Substrate alkenes. Rxn site CC bond
• Reagents
• Step 1 H() (electrophile). Role formation of
  a Markovnikov carbocation
• Step 2 X(-) (Halide F(-), Cl(-), Br(-), I(-),
  Nucleophile). Role reaction with carbocation
  from step 1. Final Result formation of an alkyl
  halide

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Addition of Hydrogen Halides to CC Bonds
(Examples)
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Hydration of CC bonds

• Substrate alkenes. Rxn site CC bond
• Reagents
• Step 1 H() (electrophile). Role formation of
  a carbocation
• Step 2 H2O or R-OH (Nucleophile). Role
  reaction with carbocation from step 1. Final
  Result formation of an alcohol or an ether

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Hydration of CC bonds (Examples)
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Electrophilic Additions to CC bonds (2)
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Oxy(Alkoxy)mercuration-Demercuration of CC bonds

• Substrate Alkenes. Rxn site CC bond
• Reagents
• Step1 Hg(2) Acetate (electrophile). Role
  Opening the CC bond. Result creation of a
  cyclic cation site mercurinium
• Step 2 H2O or R-OH (Nucleophile). Role
  reaction with cation from step1. Result
  formation of a mercury carrying alcohol or an
  ether
• Step 3 NaBH4, source of H(-). Role Replaces
  the C-Hg bond by a C-H bond. Final result an
  alcohol or an ether

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Oxy(Alkoxy)mercuration of CC bonds (Examples)
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Hydroboration-Oxidation of CC bonds

• Substrate Alkenes. Rxn site CC bond
• Reagents
• Step 1 BH3. Features source of the
  electrophile (B), and the nucleophile (H(-)).
  Events
• - B binds to the least crowded C of CC bond.
• - H binds to the least crowded C of CC bond.
• Result creation of an organoborane product
• Step 2 H2O2 (an oxidizing reagent. Role
  replaces C-B bond by a C-OH bond. Result
  formation of an anti-Markovnikov alcohol

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Hydroboration-Oxidation of CC bonds (Examples)
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Additions to cc bonds (Exercises)

• Textbook problems
• 8-47a, c, n, o
• 8-48 b, c, e
• 8-49 a, b, c, e,

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Addition of Halogens to Alkenes

• Substrate Alkenes. Rxn site CC bond
• Reagents Halogens (F2, Cl2, Br2, I2)
• Step 1 addition of the p-electrons of the
  double bond to one of the atoms of the diatomic
  halogen molecule. Result
• - Heterogeneous cleavage of the halogen bond
• - formation of a halonium ion.
• Step 2 backside attack of the halonium ion by a
  nucleophile ( eg a halogen). Result a vicinal
  dihalo molecule, halohydrin, , in anti
  conformation

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Addition of Halogens to Alkenes (General pathway)
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Addition of Halogens to Alkenes (Examples)
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3.2. Catalytic Hydrogenation of Alkenes

• Substrate Alkenes. Rxn site CC bond
• Reagents H atoms adsorbed on a catalyst (e.g.
  Pt)
• Reaction Syn addition of H atoms on the CC bond

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Catalytic Hydrogenation of Alkenes (Example)
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3.3. Epoxidation of Alkenes

• Substrate Alkenes. Rxn site CC bond
• Reagents
• Peroxy acids R-CO-OH. Feature source of
  atomic oxygen has two single electrons. Event
  syn addition of O to CC bond. Result Epoxide
  rings
• Acidic Water. Role acid-catalysed opening of
  the epoxide ring. Result Diol with the OH groups
  in anti conformation

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Epoxidation of Alkenes (General Pathway)
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Epoxidation of Alkenes (General Pathway Continued)
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Epoxidation of Alkenes and Opening of Epoxides
(Examples)
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3.4. Syn-Hydroxylation of alkenes

• Substrate Alkenes. Rxn site CC bond
• Reagents
• Osmium Tetroxide with H2O2,
• Permanganate ion in hydroxide base solution.
• Role Syn-insertion of O atoms at the CC bond.
  Result 5-atom cycles with two O atoms in
  syn-configuration
• Result Addition of two OH groups at the CC bond
  site in syn-configuration.

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Syn-Hydroxylation of alkenes (General Pathway)
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Syn-Hydroxylation of alkenes (Examples)