Towards $CH X_{3} I$ in ethanol, the correct decreasing order of nucleophilic reactivity of the four anions $C X_{6} H X_{5} S X^{-}$ , $C X_{2} H X_{5} O X^{-}$ , $Cl X^{-}$ , $F X^{-}$ is

A $C X_{2} H X_{5} O X^{-} > C X_{6} H X_{5} S X^{-} > F X^{-} > Cl X^{-}$
B $C X_{2} H X_{5} O X^{-} > F X^{-} > C X_{6} H X_{5} S X^{-} > Cl X^{-}$
C $C X_{6} H X_{5} S X^{-} > C X_{2} H X_{5} O X^{-} > Cl X^{-} > F X^{-}$
D $F X^{-} > C X_{2} H X_{5} O X^{-} > Cl X^{-} > C X_{6} H X_{5} S X^{-}$

Answer: C

The thiolate has the large, polarisable sulfur and is the best nucleophile in a protic solvent. Ethoxide is next, because it is a strongly basic and only moderately solvated oxygen anion. Chloride is less nucleophilic than ethoxide. Fluoride is tightly hydrogen bonded in ethanol and is the weakest. Basicity (

F X^{-}

and

C X_{2} H X_{5} O X^{-}

above

Cl X^{-}

) is therefore not a reliable guide in protic solvents.

Practice Organic Reaction Mechanisms III: Nucleophilic Substitution More on SN1 vs SN2: substrate, nucleophile, solvent, leaving group

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Towards CHX3​I in ethanol, the correct decreasing order of nucleophilic reactivity of the four anions CX6​HX5​SX−, CX2​HX5​OX−, ClX−, FX− is

Answer: C

More questions on SN1 vs SN2: substrate, nucleophile, solvent, leaving group

Towards $CH X_{3} I$ in ethanol, the correct decreasing order of nucleophilic reactivity of the four anions $C X_{6} H X_{5} S X^{-}$ , $C X_{2} H X_{5} O X^{-}$ , $Cl X^{-}$ , $F X^{-}$ is