The main difference between SN1 and SN2 reactions is the rate of reaction. SN1 reactions are unimolecular, meaning they involve only one molecule, and are therefore faster than SN2 reactions, which are bimolecular and involve two molecules. SN1 reactions typically occur in a single step, while SN2 reactions usually occur in two steps.
SN1 reactions are favored by polar, protic solvents, and are usually reversible. SN2 reactions, on the other hand, are favored by polar, aprotic solvents, and are usually irreversible.
The rate of SN1 reactions is dependent on the concentration of the reactants, while the rate of SN2 reactions is dependent on the concentration of both the reactants and the nucleophile.
In terms of stereochemistry, SN1 reactions can result in racemization, while SN2 reactions usually result in inversion of configuration.
Finally, SN1 reactions are typically used for the synthesis of tertiary and secondary alcohols, while SN2 reactions are typically used for the synthesis of primary alcohols.