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Step-by-step mechanism (acid-catalyzed acetal hydrolysis of cyclic acetal
Cyclic Acetal breaking mechanism in acidic condtion .jpg )
Protonation of one acetal oxygen (O gets H⁺)
This makes that C–O bond easier to break.
C–O bond cleavage (ring opening) → oxocarbenium ion
The acetal carbon becomes an oxocarbenium-like electrophile (strongly activated carbon attached to oxygen).
Water attacks the oxocarbenium carbon
Water adds to that carbon, giving a protonated hemiacetal intermediate.
Proton transfer / deprotonation
This neutralizes the intermediate and prepares the second C–O group to leave.
Protonation of the second acetal oxygen
Now the remaining "OR" part becomes a good leaving group.
Second C–O cleavage forms the carbonyl (aldehyde)
As the second C–O bond breaks, the C=O (aldehyde) is re-formed, and the second oxygen becomes an alcohol (–OH).
Deprotonation gives the final neutral product