Química Orgánica 1 · Adición a alquenos y regioquímica
Follow an oxygen-substituted alkene to a carbonyl
Condiciones: Methyl vinyl ether in aqueous acid. Hydronium and water are shown; the acid counterion is omitted. Follow acetaldehyde plus methanol formation. The original ether oxygen becomes methanol oxygen; solvent oxygen becomes carbonyl oxygen.
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Arrastra desde los electrones que se mueven hasta donde van, o toca uno y luego el otro. Cada flecha se revisa; Pista te ayuda cuando te atascas. No necesitas cuenta.
El mecanismo, paso a paso
Siguiente reproduce las flechas curvas de cada paso y las explica. Los pasos escritos están abajo.
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Enter the acid pathway
The oxygen-adjacent cation is stabilized by lone-pair donation; its carbon-cation contributor is used for capture.
Nota: Any of hydronium’s three hydrogens can be transferred.
Las flechas curvas
- The alkene π pair forms a bond to the hydrogen.
- The acid O–H bond pair stays on oxygen.
Add the solvent molecule
Retain the original methoxy group.
Nota: Either water can attack.
Las flechas curvas
- Water bonds to the oxygen-stabilized cation.
Resolve the first oxonium
The first addition product is a hemiacetal.
Nota: Water removes a proton from the positive oxygen.
Las flechas curvas
- Water uses a lone pair to take a proton from the positive oxygen.
- The O–H pair stays on oxygen, making it neutral.
Continue toward the carbonyl target
This protonation makes the methoxy fragment a neutral leaving molecule.
Las flechas curvas
- The ether oxygen accepts a proton from hydronium.
- Hydronium returns its O–H pair to oxygen.
Reorganize the hemiacetal
Couple carbonyl formation and leaving-group departure without overfilling carbon.
Las flechas curvas
- The hydroxyl oxygen pair forms the carbonyl π bond.
- The original C–O pair leaves with methanol.
Finish the carbonyl pathway
Retain methanol while regenerating the acid.
Las flechas curvas
- Water accepts the remaining carbonyl-oxygen proton.
- The O–H pair neutralizes the carbonyl oxygen.
Aldehyde, methanol, and catalyst
The original C=C π bond is replaced by a carbonyl π bond at the oxygen-bearing carbon, whose original H makes it an aldehyde. Both water hydrogens take part in proton transfers; methanol is neutral and hydronium carries the unchanged net +1 charge.
Qué vas a practicar
Complete enol-ether hydrolysis through a hemiacetal, including leaving-group activation and carbonyl formation.
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