Elimination Reactions

E2 Mechanism

• It is a single step reaction.
• The base and the alkyl halide are part of the rate determining step hence it is a bimolecular process and is termed as E2 mechanism. Halogen is the most common leaving group ( others are tosylates, brosylates)
• Base abstracts a proton from the alkyl halide

The first reaction is faster since the base abstracts a proton from the benzylic carbon resulting in a stablised carbanion. The hydrogen at the bezylic carbon is thus more acidic than in the second example.

Note: The carbanion in the first case is stabilized by resonance participation of the adjacent phenyl ring. In the second case the anion is destabilized by the +I effect of the alkyl group, hence the anion may not be formed at all.

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