E1 Mechanism

Overview:

The general form of the E1 mechanism is as follows:


B: = base
X = leaving group (usually halide or tosylate)

In the E1 mechanism, the the first step is the loss of the leaving group, which leaves in a very slow step, resulting in the formation of a carbocation. The base then attacks a neighboring hydrogen, forcing the electrons from the hydrogen-carbon bond to make the double bond. Since this mechanism involves the formation of a carbocation, rearangements can occur.

An example of the E1 reaction:

E1 Reaction

Base Strength: A strong base not required, since it is not involved in the rate-determining step

Leaving groups: A good leaving group is required, such as a halide or a tosylate, since it is involved in the rate-determining step.

Rearangements: Since the mechanism goes through a carbocation intermediate, rearangements can occur.