Addition Reactions of Alkenes

1
Addition Reactions of Alkenes

• Section 12.4 Pages 332-339

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Addition Reaction

• Addition of two atoms or groups of atoms to a
  double bond.
• R can be carbon or hydrogen.

3
Types of Addition Reactions

• The major alkene addition reactions include
• Addition of hydrogen (H2) hydrogenation
• Addition of halogens (Cl2 or Br2) halogenation
• Addition of water (H2O) hydration
• Addition of hydrogen halides (HBr or HCl)
  hydrohalogenation
• Note Double bond becomes a single bond.

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Hydrogenation Adding H2

• Double bond is broken
• H atom added to both sides of double bond
• Platinum, palladium, or nickel catalyst required
• Heat and/or pressure may also be needed

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Examples of Hydrogenation

• Hydrogenation of 1-propene to propane
• Hydrogenation of trans-2-butene

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YOU TRY THESE!

• Write hydrogenation reactions for
• 1-pentene
• 2-methyl-2-butene
• ethene

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Halogenation Adding Br2 or Cl2

• This reaction occurs easily and does not require
  a catalyst.

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Examples of Halogenation

• Bromination of 1-propene to form
  1,2-dibromopropane
• Chlorination of trans-2-butene to form
  2,3-dichlorobutane

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YOU TRY THESE!

• Write halogenation reactions for
• 1-pentene with bromine
• 2-methyl-2-butene with chlorine
• Ethene with chlorine

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Hydration Addition of H2O

• Requires a trace of acid (H) as a catalyst
• The product is an alcohol
• Markovnikovs rule applies

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Markovnikovs Rule

• A mixture of products is formed when an
  unsymmetrical alkene is hydrated.
• One product is always favored over the other.
• Vladimir Markovnikov came up with a rule to
  determine the major product formed.
• The carbon of the carbon-carbon double bond that
  originally has more hydrogen atoms receives the
  hydrogen atom being added.
• The rich get richer.

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Example of Markovnikovs Rule

• Hydration of 1-propene to form 2-propanol (major)
  and 1-propanol (minor)

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YOU TRY THESE!

• Write the hydration equation for each of the
  following molecules. Indicate the major and
  minor products for the reactions where
  applicable.
• 1-pentene
• 2-methyl-2-butene
• ethene

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Hydrohalogenation Adding HCl or HBr

• Follows Markovnikovs rule

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Examples of Hydrohalogenation

• Hydrobromination of 1-propene to form
  2-bromopropane (major) and 1-bromopropane (minor)

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YOU TRY THESE!

• Write the hydrohalogenation equation for each of
  the following molecules. Indicate the major and
  minor products for the reactions where
  applicable.
• 1-pentene with HCl
• 2-methyl-2-butene with HBr
• Ethene with HCl