Final answer:
SN1 reactions occur on tertiary alkyl halides in a two-step process where a carbocation intermediate is formed and then attacked by a nucleophile, resulting in substitution of the halogen atom.
Step-by-step explanation:
SN1 reactions occur on tertiary alkyl halides. The reaction involves a two-step process. In the first step, the alkyl halide undergoes heterolysis, forming a carbocation. In the second step, a nucleophile attacks the carbocation, resulting in the substitution of the halogen atom with the nucleophile. One important characteristic of SN1 reactions is that they proceed through a carbocation intermediate, which can lead to the formation of a racemic mixture when the reaction occurs on a chiral carbon. Secondary and primary alkyl halides do not undergo SN1 reactions.