Reactions Involving Alkenes Section 12.5 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

Oxidation Reactions Carbon-carbon double bonds are very susceptible to attack by oxidizing agents, such as potassium permanganate.

Oxidation of Ethene Because of the dramatic color change from purple to brown, this is an easy test for the presence of alkenes. (alkanes do NOT undergo the oxidation reaction and remain purple).