Addition Reactions of Alkenes Section 12 4 Pages
- Slides: 16
Addition Reactions of Alkenes Section 12. 4 Pages 332 -339
Addition Reaction n Addition of two atoms or groups of atoms to a double bond. n R can be carbon or hydrogen.
Types of Addition Reactions n The major alkene addition reactions include n Addition of hydrogen (H 2) – hydrogenation n Addition of halogens (Cl 2 or Br 2) – halogenation n Addition of water (H 2 O) – hydration n Addition of hydrogen halides (HBr or HCl) – hydrohalogenation n Note: Double bond becomes a single bond.
Hydrogenation: Adding H 2 n Double bond is broken n H atom added to both sides of double bond n Platinum, palladium, or nickel catalyst required n Heat and/or pressure may also be needed
Examples of Hydrogenation n Hydrogenation of 1 -propene to propane n Hydrogenation of trans-2 -butene
YOU TRY THESE! n Write hydrogenation reactions for: n 1 -pentene n 2 -methyl-2 -butene n ethene
Halogenation: Adding Br 2 or Cl 2 n This reaction occurs easily and does not require a catalyst.
Examples of Halogenation n Bromination of 1 -propene to form 1, 2 - dibromopropane n Chlorination of trans-2 -butene to form 2, 3 - dichlorobutane
YOU TRY THESE! n Write halogenation reactions for: n 1 -pentene with bromine n 2 -methyl-2 -butene with chlorine n Ethene with chlorine
Hydration: Addition of H 2 O n Requires a trace of acid (H+) as a catalyst n The product is an alcohol n Markovnikov’s rule applies
Markovnikov’s Rule n A mixture of products is formed when an unsymmetrical alkene is hydrated. n One product is always favored over the other. n Vladimir Markovnikov came up with a rule to determine the major product formed. n The carbon of the carbon-carbon double bond that originally has more hydrogen atoms receives the hydrogen atom being added. n “The rich get richer. ”
Example of Markovnikov’s Rule n Hydration of 1 -propene to form 2 -propanol (major) and 1 -propanol (minor)
YOU TRY THESE! n Write the hydration equation for each of the following molecules. Indicate the major and minor products for the reactions where applicable. 1 -pentene n 2 -methyl-2 -butene n ethene n
Hydrohalogenation: Adding HCl or HBr n Follows Markovnikov’s rule
Examples of Hydrohalogenation n Hydrobromination of 1 -propene to form 2 - bromopropane (major) and 1 -bromopropane (minor)
YOU TRY THESE! n 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 n 2 -methyl-2 -butene with HBr n Ethene with HCl n
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