# Which of the following mechanisms feature carbocation intermediates: SN1 only, SN2 only, E1 only, E2 only or both SN1 and E1?

May 20, 2015

Both $\text{S"_"N} 1$ and $\text{E1}$ reactions feature carbocation intermediates.

The first step in both reactions is the same: departure of the leaving group to form an intermediate carbocation.

This is the rate determining step. It is a unimolecular reaction, and that accounts for the "$1$" in the names $\text{S"_"N} 1$ and $\text{E1}$.

$\text{S"_"N"1 }$ Reaction

If the nucleophile attacks and bonds to the cationic carbon atom, we have a nucleophilic substitution ($\text{S"_"N}$) reaction.

$\text{E} 1$Reaction

If, instead, a base attacks the β hydrogen to form an alkene, we have an elimination ($\text{E1}$) reaction.