Alkene

• Alkenes


  • Properties
  • Nomenclature
  • Stability
  • Addition Reactions

  
• Ethylene


  • Electron Rich p-Bond
  • Cis and Trans
  • No rotation about p-bond

  
• Elements or Degrees of Unsaturation

  1. Bond or Ring

  
• Halogens replace Hydrogens
• C5H10Cl2 is saturated
• C6H9Br has 2 degrees of unsaturation

  
• Saturated compounds with Oxygen and Nitrogen

  • C2H6
  • C2H6O
  • C2H7N

  
• CnH2n+2


  Saturated hydrocarbons
• CnH2n+2O


  Saturated compounds with oxygen
• CnH2n+3N


  Saturated compounds with nitrogen

  
• Determine the # elements of Unsaturation

  1. C8H10Br2O

  2. C8H18 is saturated

  3. Compound is deficient by 6 "H's"

  4. 3 degrees of unsaturation

  
• Alkene Nomenclature


  • Cyclic alkenes
  • Alkyl Groups with p-Bonds
  • Alkylidene Groups
  • Double Bonds Fused to Rings
  • Polyenes

  
• cis-trans Isomers


  • E/Z System
  • Establish Priority of Substituents on Each sp2 Carbon
• Name these Alkenes


  • (Z)-4-ethyl-5-isopropyl-4-nonene

  
• Priorities with Multiple Bonds
• Name These


  • 3,3-dimethyl-1,4-cyclohexadiene
  • 2-butyl-1,5-hexadiene
  • (E) 1-ethylidene-2-methylcyclopentane
  • 3-allylcyclohexene

  
• Hydrogenation Data


  Helps to Determine Stability
• ΔHhydrogenation of Alkenes


  Enthalpy Change Shows Relative Energy of Alkene

  
• Both cis and trans 2-Butene are Hydrogenated to Butane

  
• "E" is More Stable than "Z" by 2.3 KJ/mol
• Relative Stabilities of Alkenes

  • Hyperconjugation
  • p bond associates with adjacent C-H s bond

  
• The Addition Reaction


  1. HBr Addition

  2. Markovnikov's Rule
• Addition of HBr or HCl

  • Markovnikov Addition
• Regiochemistry


  Determined by Stability of Intermediate
• 3o Carbocation forms Preferentially
• Regioisomers


  Two constitutional isomers that could result from an addition reaction
• Regiospecific


  Only one regiosisomer forms at the expense of the other
• Regioselective


  Both regioisomers are formed, but one is formed in preference