I was reading about Substitution and Elimination Reactions and I came across the following on MasterOrganicChemistry:
Polar protic solvents tend to favor elimination (E2) over substitution (SN2). Polar aprotic solvents tend to favor substitution (SN2) relative to elimination (E2).
I understand the first part. But I have trouble understanding the part with the polar aprotic solvents.
Consider the following example (from the same website):
Why is E2 not favoured? I can understand why polar aprotic solvents favour SN2:
A polar aprotic solvent like acetone or dimethylformamide preferentially solvates cations, leaving an almost "bare" nucleophile. This increases its nucleophilicity
But I could find no explanation as to why E2 does not happen because of the solvent. What keeps the nucleophile (cyanide anion here) from abstracting a beta hydrogen?