Textbook Question
SN1 substitution and E1 elimination frequently compete in the same reaction.
b. Compare the function of the solvent (methanol) in the E1 and SN1 reactions.
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8. Elimination Reactions
Nucleophiles and Basicity
Multiple Choice
Which of the following species is most likely to react as a nucleophile rather than as a base?
A
B
C
D
Verified step by step guidance1
Step 1: Understand the difference between a nucleophile and a base. A nucleophile donates an electron pair to an electrophile to form a bond, while a base abstracts a proton (H+). Both nucleophilicity and basicity involve electron pair donation, but their preferences differ based on the reaction context.
Step 2: Analyze the species given: \(\mathrm{OH_2^-}\) (hydroxide ion), \(\mathrm{Br^-}\) (bromide ion), \(\mathrm{CH_3^-}\) (methyl anion), and \(\mathrm{NH_2^-}\) (amide ion). Consider their charge density, electronegativity, and stability.
Step 3: Recognize that strong bases like \(\mathrm{CH_3^-}\) and \(\mathrm{NH_2^-}\) have high charge density and are more likely to abstract protons rather than attack electrophilic centers, making them stronger bases than nucleophiles.
Step 4: Consider \(\mathrm{Br^-}\), a larger, less basic ion with a more diffuse charge and higher polarizability, which makes it more likely to donate its electron pair to an electrophile (nucleophilic behavior) rather than abstract a proton (basic behavior).
Step 5: Conclude that among the given species, \(\mathrm{Br^-}\) is most likely to act as a nucleophile rather than as a base due to its lower basicity and higher nucleophilicity.
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