Addition Reactions of Alkenes Section 12.4 Pages

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 Addition of halogens (Cl 2 or Br 2 ) – halogenation Addition of water (H 2 O) – hydration Addition of hydrogen halides (HBr or HCl) – hydrohalogenation Note: Double bond becomes a single bond.

Hydrogenation: Adding H 2 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

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

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

Halogenation: Adding Br 2 or Cl 2 This reaction occurs easily and does not require a catalyst.

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

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

Hydration: Addition of H 2 O Requires a trace of acid (H+) as a catalyst The product is an alcohol Markovnikov’s rule applies

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.”

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

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

Hydrohalogenation: Adding HCl or HBr Follows Markovnikov’s rule

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

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