Dimethylformamide (DMF), HCON(CH3)2, is an example of a polar aprotic solvent, aprotic meaning it has no hydrogen atoms attached to highly electronegative atoms.
(c) DMF, when used as the reaction solvent, greatly enhances the reactivity of nucleophiles (e.g., CN- from sodium cyanide) in reactions like this:
NaCN + CH3CH2Br → CH3CH2C≡N + NaBr
Suggest an explanation for this effect of DMF on the basis of Lewis acid–base considerations. (Hint: Although water or an alcohol solvates both cations and anions, DMF is only effective in solvating cations.)