SN1
Introduction
The SN1 mechanism is a substitution reaction, hence the S. The N stands for nucleophilic, and the 1 stands for unimolecular.
Reagents
Substrate: 3˚>2˚>>1˚>>CH3
Solvent: polar protic is best. A polar protic solvent can act as the nucleophile (solvolysis). A polar protic solvent can stabilize any charges that form throughout the SN1 reaction (for example, the carbocation and leaving group).
Can use good/poor nucleophile
3D Sense
If the electrophilic site is a chirality center, the SN1 reaction will occur with conservation of configuration.
Mechanism
There are two core steps (in bold) and three other possible steps in an SN1 reaction:
Proton transfer
Loss of leaving group
Carbocation rearrangement
Nucleophilic attack
Proton transfer
The slow (rate-determining step) is the loss of the leaving group, which only has one reactant (the substrate), hence the unimolecular in the reaction name.
The reaction of 3,3,4-trimethylpenten-1-ol with HCl
This reaction has the following steps:
Proton transfer
Loss of leaving group
Carbocation rearrangement
Nucleophilic attack