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

- Compounds 1 and 2 are both intermediates that could form by a reaction with AgNO₃ in ethanol, but Compound 1 is less stable than Compound 2 because:

Question

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

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Compounds 1 and 2 are both intermediates that could form by a reaction with AgNO₃ in ethanol, but Compound 1 is less stable than Compound 2 because:

Quizplus · Accepted Answer

11ecba2d_1285_b55c_a3bf_4fea114c8fce_MD0008_00 The inductive effect occurs with the donation of electron density through sigma bonds. Electronegative atoms or electron withdrawing groups (EWG) pull electrons away from an adjacent atom, creating a dipole with a partial negative charge on the electronegative atom and a partial positive charge on the adjacent atom. Carbocations are stabilized by electron donating groups (EDG), such as alkyl groups, because they donate electrons toward the positively charged carbon. EWG have the opposite effect: They tend to destabilize carbocations because the electronegative atom pulls electrons toward itself, creating a partial positive charge on the adjacent atom. With two adjacent positive charges, the carbocation is not stable. Methyl (-CH₃) groups are EDG because the carbon atom is more electronegative than the adjacent hydrogen atom, creating a partial negative charge on carbon. This carbon can then donate electrons to the carbocation to stabilize it. The trifluoromethyl (-CF₃) group is an EWG because the fluorine atoms are more electronegative than the adjacent carbon and draw electrons toward themselves, creating a partial positive charge on the carbon next to the positively charged carbocation. Because Compound 1 has one EWG and Compound 2 does not contain any EWG, Compound 1 is less stable than Compound 2 due to the inductive effect from the fluorine atoms on -CF₃. (Choices A and C) The -CH₃ groups in Compound 1 are EDG, which donate electrons to the carbocation and help stabilize the carbocation. It is the -CF₃ group that withdraws electrons and destabilizes the carbocation. (Choice D) The fluorine atoms are highly electronegative and do not cause the carbocation to rearrange. Educational objective: The inductive effect occurs when electron density is donated through sigma bonds. Carbocations are stabilized by electron donating groups because they donate electrons to the positively charged carbon; they are destabilized by electron withdrawing groups because they pull electrons away from the carbocation, creating two adjacent positive charges.

Passage A Group of Students Studied the Reactivity of Four Alkyl