PRPM112: ALKENES AND ALKYNES

• alkenes and alkynes


  unstaturated hydrocarbons
• unsaturated hydrocarbons

  Fewer hydrogens per carbon than alkanes
• olefins


  also called as alkenes
• ethylene


  ripening of fruits
• α-pinene

  major component of turpentine
• β-carotene


  orange pigment, source of Vit A
• CnH2n


  general formula of alkenes
• isobutylene


  2-methylpropene
• ethylene


  ethene
• propylene


  propene
• isoprene


  2-methylbuta-1,3-diene
• ethylene

  C2H4


  fewer hydrogens-unsaturated
• ethane

  C2H6


  more hydrogen-saturated
• trans alkenes


  Question: Which is more stable?

  
  

  trans alkenes or cis alkenes
• steric (spatial)


  cis are less stable because the large substituents on the same side of the double bond which is called __________
• hydrohalogenation

  Alkyl halide, RX


  addition of HX to alkenes
• chloroethane


  ethylene reacts with HCl to give this product
• Markovnikov's Rule

  orientation of alkene addition reactions
• Markovnikov's Rule


  In the addition of HX to an alkene, the H attaches

  to the carbon with fewer alkyl substituents, and the X attaches to the carbon with more alkyl substituents (more branched).
• with more alkyl substituents (more branched)


  Markovnikov's Rule

  
  

  in the addition of HX to an alkene, c attaches to the carbon with _________
• with fewer alkyl substituents

  Markovnikov's Rule

  
  

  in the addition of HX to an alkene, the H attaches to the carbon with ____________
• regiospecific


  when only one of the two possible orientation of addition occurs
• hydration


  addition of H2O to alkenes
• Alcohols, ROH


  Alkene + Water
• H3PO4 catalyst in 250 C


  reaction of ethylene and water to ethanol
• Markovnikov addition

  oxymercuration-demercuration
• oxymercuration-demercuration

  Mercury (II) acetate in aqueous THF (tetrahydrofuran)

  
  

  Sodium borohydride
• hydroboration

  borane

  
  

  basic hydrogen peroxide
• enzymatic hydration

  fumarase
• 1,2-dihaloalkanes


  Alkene + X2
• halogenation


  addition of X2 to alkenes
• 1,2-dihaloalkanes


  Alkene + X2
• Test for Unsaturation


  Addition of Br2
• disappearance of reddish color


  positive result of test for unsaturation (addition of Br2)
• hydrogenation


  addition of H2 to Alkenes
• Alkane


  Alkenes + H2
• double bond


  this bond is hydrogenated or reduced
• reduction


  addition of H, removal of O
• palladium metal or platinum (as PtO2 )


  used as catalyst in hydrogenation
• hydroxylation


  oxidation of alkenes in addition of -OH

  
  

  **example of oxidation