arrow pushing mechanism question

Started by amimi, January 23, 2026, 02:21:11 AM

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amimi

Hello, I would appreciate some help with this!Screenshot 2026-01-22 at 11.21.06 PM.png

uma

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

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