- Protonation of the carbonyl oxygen strongly polarizes the carbonyl group and ...
- ... actives the carbonyl group for nucleophilic attact by oxygen lonepair eletrons from alchol
- Loss of a proton yields a neutral hemiacetal tetrahedral intermediate.
- Protonation of the hemiacetal hydroxyl converst it into a good leaving group
- Dehydration yields an intermediate oxonium ion.
- Addition of a second equivalent of alcohol gives protonated acetal.
- Loss of a proton yields neutral acetal product.