E2-Elimination

The E2 elimination reaction is a one-step reaction in which the leaving group leaves as the same time as the base attacks.

• Typically 1 and 2 alkyl halides and tosylates undergo E2 elimination in the presence of a strong base.
• Rate is proportional to the base and alkyl halide concentration.
  • Rate = -k [B^-][RX]
  • 2nd order kinetics
  • The following animation illustrates the elimination of H-Cl from chloroethane to yield ethene.

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• The alkyl halide must be able to adopt anti-periplanar geometry.
  • Anti-Periplanar means that the H-C-C-X atoms are in the same plane with a dihedral angle of 180^o.
  • The following applet demonstrates Anti-periplanar and Syn-periplanar configurations.

Anti-periplanar Syn-periplanar

• • The stereochemical outcome is controlled by the anti-periplanar geometry.