Passage A Group of Students Studied the Reactivity of Four Alkyl

Passage
A group of students studied the reactivity of four alkyl halides (R−X) in two nucleophilic substitution reactions.  Nucleophilic substitution reactions can go through one of two mechanisms.  The S_N2 reaction requires substitution of a leaving group with a nucleophile in a single step (Reaction 1) , and the S_N1 reaction requires elimination of the leaving group and formation of an intermediate before nucleophilic substitution can occur, resulting in a two-step process (Reaction 2) .R−X + NaI → R−I + NaX↓Reaction 1R−X + AgNO₃ → R⁺ + AgX↓ + HOCH₂CH₃ → R−OCH₂CH₃ + HNO₃Reaction 2Experiment 1The students performed the S_N2 reaction (Reaction 1) by the addition of a few drops of each alkyl halide into a separate test tube containing 1 mL of 15% solution of NaI in acetone at 25°C.  After mixing, they monitored the reaction for the formation of a precipitate (sodium halide salt) .  If no precipitate formed after 5 minutes, they raised the temperature of the reaction to 50°C and again checked for the formation of a precipitate.  Formation of a precipitate indicated the substrate underwent nucleophilic substitution.  The results observed for the Finkelstein reaction are shown in Table 1.Table 1  Results of the S_N2 Reaction
Experiment 2The students repeated the procedure followed in Experiment 1 except they added a few drops of each alkyl halide into a separate test tube containing 1 mL of 1% solution of AgNO₃ in ethanol at 25°C.  The results observed for this reaction are shown in Table 2.Table 2  Results of the S_N1 Reaction

-Suppose that Experiment 1 was done in diethyl ether instead of acetone, and NaI was replaced with another nucleophile.  The conjugate base of which of the following compounds would be the most nucleophilic?

A) CH₃(CH₂) ₂CH₃, pK_a = 50
B) (CH₃) ₂NH, pK_a = 40
C) CH₃CH₂OH, pK_a = 15.9
D) HF, pK_a = 3.2

Correct Answer:

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