Why are acetals stable to bases and nucleophiles?

Question

> Why are acetals stable to bases and nucleophiles? Could it be due to electronic effects? Lone pairs on the two oxygen atoms create an unfavorable environment for the approaching nucleophiles and bases. Or could it also be steric factors?

Answer 1

It's because alkoxides are bad leaving groups, similar to hydroxide ion. Good leaving groups are weak bases. Worse leaving groups are stronger bases. Without strong acid, the leaving group cannot be deprotonated prior to departing.

Simple ethers have similar reactivity to acetals under basic/nucleophilic conditions. In acid, acetals are usually more reactive because they can form resonance stabilized oxocarbenium ions.