Is ethoxide a better nucleophile in methanol or acetone?

1 Answer
Aug 3, 2015


Ethoxide is a better nucleophile in acetone.


The solvent affects the nucleophilicity of ethoxide ion.

A polar protic solvent like methanol can participate in hydrogen bonding with a nucleophile like ethoxide ion, creating a “shell” of solvent molecules around the ion.

This decreases the nucleophilicity of the ethoxide, because the nucleophile must push these solvent molecules out of the way in order to attack the substrate.

A polar aprotic solvent like acetone does not hydrogen bond to ethoxide ion to a significant extent.

Polar Aprotic

So the ethoxide ion is almost a "bare" nucleophile.

It is better able to attack the substrate and is therefore a stronger nucleophile.

WARNING: Ethoxide ion is also a strong base, so you will get a competing reaction in acetone — the aldol condensation.