Scelta multipla
Which of the following species is the least nucleophilic?
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8. Elimination Reactions
Nucleophiles and Basicity
Scelta multipla
Which of the following reagents is the best choice to convert an alkyl bromide to an alcohol via an S mechanism?
A
Aqueous
B
in ethanol
C
Water () only
D
Concentrated
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Identify the goal: converting an alkyl bromide (a good leaving group) into an alcohol via an S_N2 mechanism, which involves a nucleophilic substitution where the nucleophile attacks the electrophilic carbon and displaces the leaving group in one step.
Recall that for an S_N2 reaction, the nucleophile should be strong and negatively charged to effectively attack the carbon bearing the leaving group. Also, the solvent should ideally be polar aprotic to favor the S_N2 pathway, but aqueous conditions can still work if the nucleophile is strong enough.
Evaluate each reagent option:
- Aqueous NaOH provides hydroxide ions (OH⁻), a strong nucleophile that can attack the alkyl bromide to form the alcohol.
- NaOEt in ethanol provides ethoxide ions (EtO⁻), which are strong nucleophiles but will produce an ether rather than an alcohol.
- Water (H₂O) is a weak nucleophile and would lead to a slower reaction.
- Concentrated H₂SO₄ is acidic and would likely lead to elimination or other side reactions rather than substitution.
Conclude that aqueous NaOH is the best choice because it supplies a strong nucleophile (OH⁻) that can perform a clean S_N2 substitution on the alkyl bromide to yield the alcohol.
Remember that the S_N2 mechanism proceeds with inversion of configuration at the carbon center, so if the alkyl bromide is chiral, the product alcohol will have inverted stereochemistry.
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