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Passage A Group of Students Studied the Reactivity of Four Alkyl

Question 22

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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 SN2 reaction requires substitution of a leaving group with a nucleophile in a single step (Reaction 1) , and the SN1 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 SN2 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 SN2 Reaction
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<sub>N</sub>2 reaction requires substitution of a leaving group with a nucleophile in a single step (Reaction 1) , and the S<sub>N</sub>1 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↓<strong>Reaction 1</strong>R−X + AgNO<sub>3</sub> → R<sup>+</sup> + AgX↓ + HOCH<sub>2</sub>CH<sub>3</sub> → R−OCH<sub>2</sub>CH<sub>3</sub> + HNO<sub>3</sub><strong>Reaction 2</strong>Experiment 1The students performed the S<sub>N</sub>2 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.<strong>Table 1</strong>  Results of the S<sub>N</sub>2 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 AgNO<sub>3</sub> in ethanol at 25°C.  The results observed for this reaction are shown in Table 2.<strong>Table 2</strong>  Results of the S<sub>N</sub>1 Reaction -Which of the following statements is NOT supported by the results in Tables 1 and 2? A) In Experiment 2, crotyl chloride forms a stable carbocation. B) Primary alkyl halides react more readily in S<sub>N</sub>2 reactions than in S<sub>N</sub>1 reactions. C) Nucleophilic substitution reactions are not dependent on the substrate (alkyl halide) substitution. D) Bromide is a better leaving group than chloride and enhances reactivity in less favorable reactions. 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 SN1 Reaction
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<sub>N</sub>2 reaction requires substitution of a leaving group with a nucleophile in a single step (Reaction 1) , and the S<sub>N</sub>1 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↓<strong>Reaction 1</strong>R−X + AgNO<sub>3</sub> → R<sup>+</sup> + AgX↓ + HOCH<sub>2</sub>CH<sub>3</sub> → R−OCH<sub>2</sub>CH<sub>3</sub> + HNO<sub>3</sub><strong>Reaction 2</strong>Experiment 1The students performed the S<sub>N</sub>2 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.<strong>Table 1</strong>  Results of the S<sub>N</sub>2 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 AgNO<sub>3</sub> in ethanol at 25°C.  The results observed for this reaction are shown in Table 2.<strong>Table 2</strong>  Results of the S<sub>N</sub>1 Reaction -Which of the following statements is NOT supported by the results in Tables 1 and 2? A) In Experiment 2, crotyl chloride forms a stable carbocation. B) Primary alkyl halides react more readily in S<sub>N</sub>2 reactions than in S<sub>N</sub>1 reactions. C) Nucleophilic substitution reactions are not dependent on the substrate (alkyl halide) substitution. D) Bromide is a better leaving group than chloride and enhances reactivity in less favorable reactions.
-Which of the following statements is NOT supported by the results in Tables 1 and 2?


A) In Experiment 2, crotyl chloride forms a stable carbocation.
B) Primary alkyl halides react more readily in SN2 reactions than in SN1 reactions.
C) Nucleophilic substitution reactions are not dependent on the substrate (alkyl halide) substitution.
D) Bromide is a better leaving group than chloride and enhances reactivity in less favorable reactions.

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