The steric hindrances make the tertiary substrates practically inert towards the SN2 mechanism. However, it is observed that these substrates react at an important rate with water, following first order kinetics.
This experimental observation implies proposing a new mechanism, called SN1, which occurs with tertiary substrates and poor nucleophiles, facts that are impossible to explain using the SN2 mechanism.
This reaction is not compatible with an SN2 mechanism, since the substrate is tertiary, the nucleophile is bad, and the rate depends only on the substrate.
In the next sections we will see a new mechanism compatible with these experimental facts.
Other reactions that occur through the SN1 mechanism are:
