What solvent is used in the SN2 reaction of an alkyl bromide with cyanide in the described example?

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Multiple Choice

What solvent is used in the SN2 reaction of an alkyl bromide with cyanide in the described example?

In SN2 with cyanide, the speed hinges on how reactive the cyanide ion remains as a nucleophile. Polar aprotic solvents are best because they don’t form strong hydrogen bonds with the anion, so CN− stays highly nucleophilic and attacks the alkyl halide efficiently. Water and ethanol are protic solvents; they hydrogen-bond to the cyanide and greatly reduce its nucleophilicity, slowing the SN2 process. Acetone is polar aprotic, which would seem suitable, but cyanide salts don’t dissolve well in it, limiting the reaction. DMF is a polar aprotic solvent that dissolves both inorganic cyanide salts and the alkyl bromide well, while not heavily solvating CN−. This keeps CN− highly reactive and facilitates a rapid SN2 attack, which is why it’s the solvent described in this example.

In SN2 with cyanide, the speed hinges on how reactive the cyanide ion remains as a nucleophile. Polar aprotic solvents are best because they don’t form strong hydrogen bonds with the anion, so CN− stays highly nucleophilic and attacks the alkyl halide efficiently.

Water and ethanol are protic solvents; they hydrogen-bond to the cyanide and greatly reduce its nucleophilicity, slowing the SN2 process. Acetone is polar aprotic, which would seem suitable, but cyanide salts don’t dissolve well in it, limiting the reaction.

DMF is a polar aprotic solvent that dissolves both inorganic cyanide salts and the alkyl bromide well, while not heavily solvating CN−. This keeps CN− highly reactive and facilitates a rapid SN2 attack, which is why it’s the solvent described in this example.

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