Organic Chemistry: Elimination Reactions

Elimination Reactions

E1 Mechanism

• A two-step mechanism involving a carbocation intermediate
• Rate-determining step is the formation of the carbocation (first step)
• Second step is the loss of a leaving group to form a π bond
• E1 reactions are typically favored in:
  • Tertiary alkyl halides
  • Polar solvents
  • Higher temperatures

E2 Mechanism

• A one-step mechanism involving a concerted transition state
• Rate-determining step is the simultaneous formation of the π bond and loss of the leaving group
• E2 reactions are typically favored in:
  • Secondary alkyl halides
  • Strong bases (e.g. NaOH, KOtBu)
  • Lower temperatures

Stereochemistry

• Elimination reactions can proceed with either syn or anti periplanar geometry
• Stereoselectivity can be influenced by:
  • Substrate structure
  • Base strength
  • Solvent effects
• Stereospecificity can be observed in certain reactions, where the stereochemistry of the starting material is retained in the product

Organic Synthesis

• Elimination reactions are an important tool in organic synthesis for:
  • Forming alkene bonds
  • Introducing unsaturation
  • Creating complex molecular structures
• Elimination reactions can be used in combination with other reactions to achieve complex synthetic goals

Alkene Reactions

• Alkenes can undergo addition reactions, including:
  • Electrophilic addition (e.g. HCl, Br2)
  • Nucleophilic addition (e.g. H2O, ROH)
• Alkenes can also undergo oxidation reactions, including:
  • Epoxidation (e.g. m-CPBA)
  • Hydroxylation (e.g. OsO4)
• Alkenes can be used as starting materials for further functionalization, such as:
  • Alkyne formation (e.g. Corey-Fuchs reaction)
  • Cycloaddition reactions (e.g. Diels-Alder reaction)