The question asks which factors determine if a haloalkane undergoes an \(S_{N2}\) or \(S_{N1}\) reaction. Here's a step-by-step explanation of the relevant concepts:
Understanding \(S_{N2}\) and \(S_{N1}\) Reactions:
\(S_{N2}\) (Substitution Nucleophilic Bimolecular) reaction is a single-step process where the nucleophile attacks the substrate and the leaving group departs simultaneously. This type of reaction involves a transition state where the carbon atom is simultaneously bonded to the nucleophile and the leaving group.
\(S_{N1}\) (Substitution Nucleophilic Unimolecular) reaction, on the other hand, is a two-step process. First, the leaving group departs to form a carbocation intermediate, followed by the attack of the nucleophile.
Influence of Solvent on Reaction Type:
\(S_{N2}\) reactions are favored in polar aprotic solvents because these solvents do not form strong interactions with the nucleophile, thus making it more nucleophilic.
\(S_{N1}\) reactions are favored in polar protic solvents which stabilize the carbocation intermediate and the leaving group through hydrogen bonding.
Analyzing Other Options:
Low temperature: While temperature can influence reaction rates, it does not directly determine whether an \(S_{N2}\) or \(S_{N1}\) mechanism is preferred.
The type of halogen atom: The leaving ability of a halogen atom can affect the rate but does not decide the type of nucleophilic substitution (though better leaving groups favor both types).
Stability of the haloalkane: While more stable carbocations (tertiary) favor \(S_{N1}\), stability alone does not determine the mechanism without considering solvent effects.
Conclusion: The most influential factor determining whether a haloalkane undergoes an \(S_{N2}\) or \(S_{N1}\) reaction is the solvent used in the reaction, as it directly influences the mechanisms described above.
