Basics of E2 elimination reaction

The E2 elimination is a type of elimination reaction in organic chemistry. It takes place in only 1 step, but the rate of the reaction is limited by two of the reactants. Figure 1 here provides an example of an E1 elimination.

The leaving group takes the electrons and detaches from the main molecule as a base simultaneously abstracts a proton. Notice there is no intermediate formation of a carbocation.

Figure 1. Example of an E2 elimination reaction, using 2-bromobutane as the main reactant.

Important factors that influence E2 reactivity

E2 eliminations are for many factors influenced in a similar way for as for the E1 type.

Noteworthy differences are:

  • Degree of substitution: Even though elimination reactions are generally more favored in highly substituted molecules, E2 reactions can also take place with secondary and even primary carbon atoms.

  • It usually requires a strong base.

Stereochemistry of the reaction product

As the E2 reaction takes place in a single step, the reaction product will all have the same configuration, and the product with trans configuration will be far more dominant. This iis due to the fact that the leaving group and the base-removed hydrogen will tend to be antiperiplanar, that is, on opposite sides of the bond of the two carbons that the involved groups are connected to. This is a special trait of the E2 reaction.