Alkenes

• Alkenes

  • Unsaturated hydrocarbons
  • CnH2n
  • Doubles bonds have ‘high electron density’ - reactive
• Electrophilic addition


  • Alkenes attacked by electrophiles due to their double bond
  • Double bond has a high density of electrons
  • Electrophiles adds to the molecule
• What is an electrophile

  • An electron pair acceptor
  • Deficient in electrons & attracted to double bond
• Colour change when bromine is added to an alkene

  Brown-orange —> colourless
• Electrophillic addition of Alkenes with H-Br :

  
• Major & Minor products :

  Most stable. Least stable

  Tertiary > secondary > primary

  
• Electrophilic addition in Alkenes:

  
• What type of hydrocarbons are alkenes?

  Unsaturated hydrocarbons
• What is the general formula for alkenes?

  C$n$H$2n$
• What does the general formula for alkenes apply to?

  One double bond in the molecule
• How do alkenes differ from alkanes?

  Alkenes contain double bonds
• What type of reactions do alkenes undergo?

  Addition reactions
• What is the structural formula for ethene?

  • Ethene: C$2$H$4$
  • Structural formula: H$2$C=CH$2$
• What is the structural formula for buta-1,3-diene?

  • Buta-1,3-diene: C$4$H$6$
  • Structural formula: H$2$C=CH-CH=CH$2$
• Why are alkenes reactive?

  They have high electron density in double bonds
• What are cycloalkenes?

  Cyclic alkenes with two fewer hydrogens
• What is an electrophile?

  An electron pair acceptor
• What are examples of electrophiles?

  H⁺, NO₂⁺
• What do curly arrows represent in reaction mechanisms?

  Movement of electron pairs
• What happens when bromine water is added to an alkene?

  It decolorizes from brown to colorless
• What is formed when bromine adds to an alkene?

  Di-bromoalkane
• What is a carbocation?

  A positively charged carbon intermediate
• How does the stability of a carbocation affect product formation?

  More stable carbocations lead to more products
• What type of carbocation is more stable?

  Tertiary carbocation
• What is the mechanism for the addition of hydrogen halides to alkenes?

  1. Electrophile attacks double bond
  2. Carbocation intermediate forms
  3. Halide ion attacks carbocation
  4. Halogenoalkane product formed
• What is the product when alkenes react with sulfuric acid?

  Alkyl hydrogen sulfate
• What is the formula for sulfuric acid?

  H₂SO₄
• What is the role of sulfuric acid in alkene reactions?

  • Acts as a catalyst
  • Converts alkenes to alcohols
• What is the product formed when alkenes react with cold concentrated sulfuric acid?

  Alkyl hydrogen sulfates
• What role does sulfuric acid play in the reaction with alkenes?

  It acts as a catalyst
• What is produced when alkyl hydrogen sulfate is hydrolyzed?

  Ethanol
• What is the mechanism that shows how sulfuric acid interacts with alkenes?

  It forms an intermediate called alkyl hydrogen sulfate
• What is the chemical formula for sulfuric acid?

  H₂SO₄
• What happens to the double bond in alkenes during the reaction with sulfuric acid?

  The double bond becomes a single bond
• What is the term for the process of adding water to alkyl hydrogen sulfate to form ethanol?

  Hydrolysis
• What does the term "hydrolysis" mean in this context?

  Breaking a bond using water
• What is the overall reaction when alkenes react with sulfuric acid and water?

  Alkene + H₂SO₄ + H₂O → Ethanol + H₂SO₄
• What type of alkenes can produce two products during reactions?

  Asymmetric alkenes
• What are alkenes considered in the context of plastics?

  They are monomers
• What process do monomers undergo to form polymers?

  Addition polymerization