E2 mechanism (E-elimination, 2-second order) is one of the three limiting mechanisms of 1,2-elimination. It is a one step mechanism.
* Only the leaving group and one beta hydrogen are shown for clarity.
A 1,2-elimination occurring via E2 mechanism is called and E2 reaction. The rate law of an E2 reaction is
rate = k [substrate][base]
According to the rate law, an E2 reaction is second order overall, and the concentrations of both substrate and base affect the rate of reaction, which is consistent with the single-step mechanism.