How a First-Order Substitution Reaction Occurs
A first-order (or SN1) substitution reaction occurs when one group on an organic molecule leaves and is later substituted by another group. This reaction goes through a carbocation intermediate. The SN1 mechanism is analogous to breaking up with your current significant other, staying single for a while, and only after you’ve been single, becoming attached to a new romantic partner.
The likelihood of an SN1 reaction occurring depends on the solvent, the nature of the substrate, and the substituting group (called the nucleophile, or nucleus lover, sometimes abbreviated Nuc). As the name SN1 indicates, it requires a Substitution by a Nucleophile in which 1 reactant determines the rate of the reaction. The SN1 mechanism is shown here.