For each pair, choose the haloalkane that would react most quickly in an S_N1 or E1 reaction.
(b)

Sₙ1 (nucleophilic substitution unimolecular) and E1 (elimination unimolecular) reactions are two types of reactions that involve a two-step mechanism. In Sₙ1 reactions, the rate-determining step is the formation of a carbocation intermediate, while in E1 reactions, the same intermediate is formed before the elimination of a leaving group. Both reactions are favored by tertiary haloalkanes due to their ability to stabilize the carbocation.

Carbocation stability is a crucial factor in determining the rate of Sₙ1 and E1 reactions. Tertiary carbocations are more stable than secondary or primary ones due to hyperconjugation and inductive effects from surrounding alkyl groups. The more stable the carbocation, the faster the reaction will proceed, making the structure of the haloalkane significant in predicting reactivity.

The ability of a leaving group to depart from the haloalkane is essential in both Sₙ1 and E1 reactions. Good leaving groups, such as iodide or bromide, can stabilize the transition state and facilitate the formation of the carbocation. The strength of the leaving group can significantly influence the reaction rate, with weaker bases generally being better leaving groups.