Química Orgânica 2 · Acetais, iminas e equilíbrios relacionados
Imine formation — ethanal and ammonia
Condições: Ethanal and ammonia in mildly acidic conditions, with water removal to favor imine formation. Draw the steps that make the imine; proton exchange between acid and free ammonia is not shown. 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.
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Protonate the carbonyl
Hydronium protonates the carbonyl oxygen, making the carbonyl carbon easier to attack.
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.
Ammonia attacks
Nitrogen uses its lone pair to attack the carbonyl carbon. Nitrogen now has four bonds and a positive charge.
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.
Remove a nitrogen proton
Water removes a proton from the positively charged nitrogen. This gives a neutral carbinolamine: a carbon bonded to both OH and nitrogen.
As setas curvas
- The base uses a lone pair to accept a proton from the N–H bond.
- The bond to hydrogen breaks, and its electrons stay on the atom losing the proton.
Turn OH into water
Add a proton to the OH group so it can leave as water.
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.
Form the C=N bond
The nitrogen lone pair forms the C=N bond as water leaves. Nitrogen carries a positive charge in this iminium ion.
As setas curvas
- A lone pair forms the new π bond.
- The leaving group takes the electrons from the single bond.
Return the acid catalyst
Water removes a proton from the iminium nitrogen. This gives the neutral C=N product and regenerates hydronium.
As setas curvas
- The base uses a lone pair to accept a proton from the N–H bond.
- The bond to hydrogen breaks, and its electrons stay on the atom losing the proton.
Products
The imine nitrogen has a C=N double bond, one N–H bond and one lone pair. The original carbonyl oxygen leaves in water with two hydrogens. Hydronium is regenerated.
O que você vai praticar
Add ammonia to an aldehyde, then lose water to form a C=N bond.
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