CHEM 102 Lecture Notes - Lecture 4: Elimination Reaction, Leaving Group, Molecularity
Document Summary
There is two mechanisms for elimination: e1 describes an elimination reaction (e) in which the rate-determining step is unimolecular (1) and does not involve the base. The leaving group leaves in this step, and the proton is removed in a separate second step: e2 describes an elimination (e) that has a bimolecular (2) rate-determining step that must involve the base. Loss of the leaving group is simultaneous with removal of the proton by the base. There are a number of factors that affect whether an elimination goes by an e1 or e2 mechanism. One is immediately obvious from the rate equations: only the e2 is affected by the concentration of base, so at high base concentration e2 is favoured. If you see a strong base being used for an elimination, it is certainly an e2 reaction. We have already mentioned the bulky t-butoxide ideal for promoting e2 as it"s both bulky and a strong base (pkah = 18).
