Question

Would you expect acetate ion (CH3CO2−) to be a better nucleophile in an SN2 reaction with an alkyl halide carried out in methanol or in dimethyl sulfoxide?

Accepted Answer

Understand the role of the solvent in an SN2 reaction: In an SN2 reaction, the nucleophile attacks the electrophilic carbon of the alkyl halide in a single concerted step. The solvent can significantly influence the nucleophilicity of the nucleophile. Polar aprotic solvents enhance nucleophilicity, while polar protic solvents can hinder it by stabilizing the nucleophile through hydrogen bonding. Analyze the solvents given: Methanol (CH3OH) is a polar protic solvent, meaning it has hydrogen atoms capable of forming hydrogen bonds with the nucleophile. Dimethyl sulfoxide (DMSO, (CH3)2SO) is a polar aprotic solvent, meaning it does not have hydrogen atoms that can form hydrogen bonds, but it can stabilize cations without significantly stabilizing the nucleophile. Consider the acetate ion (CH3CO2−): The acetate ion is a negatively charged nucleophile. In a polar protic solvent like methanol, the acetate ion will be stabilized by hydrogen bonding, reducing its nucleophilicity. In contrast, in a polar aprotic solvent like DMSO, the acetate ion will not be stabilized by hydrogen bonding, allowing it to remain more reactive as a nucleophile. Relate solvent effects to the SN2 reaction: Since SN2 reactions are favored by strong nucleophiles, the acetate ion will be a better nucleophile in DMSO (polar aprotic solvent) compared to methanol (polar protic solvent). This is because DMSO does not hinder the nucleophile's reactivity, whereas methanol does. Conclude the comparison: Based on the solvent effects, the acetate ion (CH3CO2−) would be a better nucleophile in an SN2 reaction with an alkyl halide when the reaction is carried out in dimethyl sulfoxide (DMSO) rather than in methanol.

Would you expect acetate ion (CH₃CO₂⁻) to be a better nucleophile in an S_N2 reaction with an alkyl halide carried out in methanol or in dimethyl sulfoxide?

비슷한 문제에 대한 검증된 영상 답변:

주요 개념

Nucleophilicity

Solvent Effects

S<sub>N</sub>2 Mechanism