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Addition Reactions of Alkenes

Addition Reactions of Alkenes. Section 12.4 Pages 332-339. Addition Reaction. Addition of two atoms or groups of atoms to a double bond. R can be carbon or hydrogen. Types of Addition Reactions. The major alkene addition reactions include Addition of hydrogen (H 2 ) – hydrogenation

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Addition Reactions of Alkenes

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  1. Addition Reactions of Alkenes Section 12.4 Pages 332-339

  2. 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.

  4. 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

  5. Examples of Hydrogenation • Hydrogenation of 1-propene to propane • Hydrogenation of trans-2-butene

  6. YOU TRY THESE! • Write hydrogenation reactions for: • 1-pentene • 2-methyl-2-butene • ethene

  7. Halogenation: Adding Br2 orCl2 • This reaction occurs easily and does not require a catalyst.

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

  9. YOU TRY THESE! • Write halogenation reactions for: • 1-pentene with bromine • 2-methyl-2-butene with chlorine • Ethene with chlorine

  10. Hydration: Addition of H2O • Requires a trace of acid (H+) as a catalyst • The product is an alcohol • Markovnikov’s rule applies

  11. Markovnikov’s 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.”

  12. Example of Markovnikov’s Rule • Hydration of 1-propene to form 2-propanol (major) and 1-propanol (minor)

  13. 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

  14. Hydrohalogenation: Adding HCl or HBr • Follows Markovnikov’s rule

  15. Examples of Hydrohalogenation • Hydrobromination of 1-propene to form 2-bromopropane (major) and 1-bromopropane (minor)

  16. 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

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