In which of the solvents below would the reaction shown take place at the fastest rate?
A. ethanol B. acetic acid C. dimethyl sulfoxide
This is a substitution reaction since we replace Br with CN. The substrate is primary ( Br is attached to carbon which is attached to one carbon only). SN2 prefers a primary substrate. Therefore, this reaction is an SN2 reaction. SN2 reaction wants polar aprotic solvents such as: acetone, DMSO, DMF, and ethers. Polar aprotic solvents do not have acidic hydrogens. Dimethyl sulfide is the only polar aprotic solvent, choice C.