Química Orgânica 2 · Acetais, iminas e equilíbrios relacionados
Recover a ketone from its acetal
Condições: Acetone dimethyl acetal in excess acidic water; follow hydrolysis to acetone and two methanol molecules. Counterions are not drawn; no stereochemistry is assigned without bond markers.
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Arraste dos elétrons que se movem até onde eles vão, ou toque em um e depois no outro. Cada seta é verificada; Dica ajuda quando você travar. Não precisa de conta.
O mecanismo, passo a passo
Próximo mostra as setas curvas de cada passo e as explica. Os passos escritos estão abaixo.
Ler todos os 8 passos escritos
Move the electrons
Protonate an acetal oxygen so it can leave as methanol.
As setas curvas
- The base uses a lone pair to accept a proton from the O–H bond.
- The bond to hydrogen breaks, and its electrons stay on the atom losing the proton.
Move the electrons
One alcohol departs while the remaining ether oxygen stabilizes the oxocarbenium contributor.
As setas curvas
- A lone pair forms the new π bond.
- The leaving group takes the electrons from the single bond.
Move the electrons
Water captures the cationic carbon and becomes the carbonyl oxygen in the eventual ketone.
As setas curvas
- The nucleophile uses a lone pair to form the new single bond.
- The π electrons move off carbon, keeping eight electrons around it.
Move the electrons
Solvent deprotonates the water-derived oxonium to give a hemiacetal.
As setas curvas
- The base uses a lone pair to accept a proton from the O–H bond.
- The bond to hydrogen breaks, and its electrons stay on the atom losing the proton.
Move the electrons
The remaining methoxy oxygen becomes an alcohol leaving group.
As setas curvas
- The base uses a lone pair to accept a proton from the O–H bond.
- The bond to hydrogen breaks, and its electrons stay on the atom losing the proton.
Move the electrons
Water-derived oxygen reforms the carbonyl as the second methanol molecule leaves.
As setas curvas
- A lone pair forms the new π bond.
- The leaving group takes the electrons from the single bond.
Move the electrons
The carbonyl oxonium loses its remaining proton and returns hydronium.
As setas curvas
- The base uses a lone pair to accept a proton from the O–H bond.
- The bond to hydrogen breaks, and its electrons stay on the atom losing the proton.
Products
The ketone oxygen comes from incoming water, not either original acetal oxygen. Both original C–O bonds are cleaved while both O–methyl bonds survive; hydronium is regenerated.
O que você vai praticar
Follow both leaving alcohols and identify the water-derived carbonyl oxygen.
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