The E2 reaction – Second Order Elimination

How does it work?

B = base

X = leaving group

     This is a one step process.  The base attacks a hydrogen on the carbon neighboring the carbon with the leaving group, pushes the electrons to a double bond as the leaving group leaves. 

Does Steric Hinderance affect this reaction?

Steric hinderance does not greatly affect E2 reactions.  Therefore, highly substituted carbon chains, which form the most stable alkenes, will undergo E2 easily.

What must happen for the pi bond to form?

In order for the pi bond to form, the p-orbitals must be parallel. 

What is the geometry of the intermediate?

The intermediate form an anti-periplanar geometry.

Why is it called a second order reaction?

It is called second order because the rate depends on both the substrate and the base.

What type of base does this reaction favor?

A strong base is favored in this reaction because it is better able to remove a proton

What type of substrate works best in this reaction?

Highly substituted substrates will work the best in this reaction:3^o > 2^o > 1^o > methyl

Because a good base has more difficulty reaching the carbon for substitution.

Can rearrangement occur?

Since E2 does not go by carbocation intermediate, no rearrangements can occur.