Question

multiple choice 1 point
which of the following would be the best solvent for an s_n2 reaction involving sodium iodide (nal) and an alkyl bromide?
water
acetone
ethanol
benzene
previous

Explanation:

Step1: Understand the nature of SN2 reaction

SN2 reactions favor polar aprotic solvents. Polar aprotic solvents can solvate cations (like \(Na^+\) from \(NaI\)) but do not strongly solvate anions (like \(I^-\)). This allows the anion (\(I^-\)) to be more "free" and nucleophilic.

Step2: Analyze each solvent

• Water: It is a polar protic solvent. Protic solvents have \( -OH\) groups (in water, \(H - O - H\)). They can hydrogen - bond with anions (\(I^-\)), making the anion less nucleophilic.
• Acetone (\(CH_3COCH_3\)): It is a polar aprotic solvent. It has a polar \(C = O\) group (which can solvate cations) but no \( - OH\) or \( - NH\) groups to hydrogen - bond with anions. So, \(I^-\) remains more nucleophilic.
• Ethanol (\(C_2H_5OH\)): It is a polar protic solvent. The \( - OH\) group can hydrogen - bond with \(I^-\), reducing its nucleophilicity.
• Benzene (\(C_6H_6\)): It is a non - polar solvent. In an SN2 reaction involving \(NaI\) (an ionic compound), \(NaI\) will not dissolve well in a non - polar solvent. Good solubility of reactants (\(NaI\) and alkyl bromide) is required for the reaction to occur. Since \(NaI\) is ionic, a polar solvent is needed for its dissolution.

So, acetone is the best solvent for the given \(S_N2\) reaction.

Answer:

B. Acetone