8. Elimination Reactions

Which of the following charged nucleophiles is most reactive in $\mathrm{DMSO}$ solvent?

Which of the following molecules is a negatively charged nucleophile?

In aqueous solution, rank the following species in order of increasing nucleophilicity: $F_{-}$, ${\mathrm{Cl}}_{-}$, ${\mathrm{Br}}_{-}$, $I_{-}$.

Which of the following correctly ranks the nucleophilicity of the species $F_{-}$, ${\mathrm{Cl}}_{-}$, ${\mathrm{Br}}_{-}$, and $I_{-}$ in water from greatest to least?

Which of the following species is most likely to react as a nucleophile rather than as a base?

Which of the following reagents is the best choice to convert an alkyl bromide to an alcohol via an S$N_2$ mechanism?

Which of the following species is the least nucleophilic?

Which is a better nucleophile?

c. CH₃O⁻ or CH₃OH in H₂O

For each pair, predict the stronger nucleophile in the SN2 reaction (using an alcohol as the solvent). Explain your prediction.

e. (CH₃)₃N or (CH₃)₂O

f. CH₃COO^– or CF₃COO^–

For each pair, predict the stronger nucleophile in the SN2 reaction (using an alcohol as the solvent). Explain your prediction.

c. NH₃ or PH₃

d. CH₃S^– or H₂S

[FIGURE: KEY MECHANISM 7-1]

Show what happens in step 2 of the example if the solvent acts as a nucleophile (forming a bond to carbon) rather than as a base (removing a proton).

a. Which is a stronger base: RO⁻ or RS⁻?

b. Which is a better nucleophile in an aqueous solution?

c. Which is a better nucleophile in DMSO?

Which is a better nucleophile?

e. HO⁻ or ^-NH₂ in NH₃

f. HO⁻ or ^-NH₂ in DMSO

Which member of each pair is a better nucleophile in methanol?

e. I⁻ or Br⁻

f. Cl⁻ or Br⁻

Rank the following species in each set from best nucleophile to poorest nucleophile.

c. H₂O and NH₃ in methanol

d. Br⁻, Cl⁻, I⁻ in methanol