Química Orgânica 2 · Adição e condensação aldólica
Cyclopent-1-ene-1-carbaldehyde from hexanedial
Condições: NaOH, H2O, Δ
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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 7 passos escritos
Hydroxide forms the enolate
Hydroxide removes an α-hydrogen next to one aldehyde group. The two ends of the molecule are identical, so either end can serve as the donor.
As setas curvas
- Hydroxide takes an α-hydrogen.
- The C–H pair forms the enolate C=C bond.
- The C=O π pair moves onto oxygen.
Five-membered ring closure
The enolate carbon attacks the other aldehyde carbon of the same chain. The new bond closes a five-membered ring (the α-carbon, three CH2 groups and the attacked carbon).
As setas curvas
- The oxygen lone pair re-forms the aldehyde C=O.
- The enolate π pair forms the ring C–C bond.
- The aldehyde π pair moves onto oxygen.
Protonation of the alkoxide
Water protonates the alkoxide, giving 2-hydroxycyclopentane-1-carbaldehyde and regenerating hydroxide.
As setas curvas
- The alkoxide takes a proton from water.
- The O–H pair stays on oxygen as hydroxide.
Enolization at the ring carbon
Hydroxide removes the ring hydrogen α to the aldehyde, which is also next to the carbinol carbon.
As setas curvas
- Hydroxide takes the α-hydrogen.
- The C–H pair forms the enolate C=C bond.
- The C=O π pair moves onto oxygen.
Where does the C=C end up?
E1cB places the new double bond between the α- and β-carbons.
E1cB loss of hydroxide
The enolate re-forms C=O and expels hydroxide from the β-carbon, giving the ring C=C conjugated with the aldehyde.
As setas curvas
- The oxygen lone pair re-forms the C=O.
- The enolate π pair forms the ring C=C bond.
- The C–O pair leaves as hydroxide.
Cyclopent-1-ene-1-carbaldehyde
Cyclopent-1-ene-1-carbaldehyde forms; five-membered rings like this one form readily in intramolecular aldols.
O que você vai praticar
Draw the intramolecular aldol condensation of hexanedial: C2 enolate formation, five-membered ring closure onto the other aldehyde, protonation and E1cB dehydration to cyclopent-1-ene-1-carbaldehyde.
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