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