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The E2 Reaction

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E2 Rate and Transition State

The rate law of the above E2 reaction follows:

In the E2 reaction, a base removes a β -hydrogen, forms a double bond and kicks out the leaving group. The reaction occurs through a concerted mechanism and requires a β -hydrogen. This mechanism is also called β -elimination.

The E2 rate law is first order for both reactants. Here's the simplest possible transition state:

E2 Stereochemistry

As in the SN2 reaction, the mechanism of transition state formation can be deduced using a stereocenter. There are two possible modes of reactivity that yield two different stereoisomers.

In syn elimination, the base attacks the β -hydrogen on the same side as the leaving group.

In anti elimination, the base attacks the β -hydrogen on the opposite side of the leaving group.

It has been experimentally determined that E2 elimination occurs through an anti mechanism.