Química Orgânica 2 · Acetais, iminas e equilíbrios relacionados
A diol protects an aldehyde
Condições: Benzaldehyde plus ethylene glycol with catalytic acid and water removal. The two alcohol groups belong to the same diol. Counterions are not drawn; no stereochemistry is assigned without bond markers.
Desenhe este problema você mesmo
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
Hydronium gives a proton to the carbonyl oxygen, making the carbonyl easier to attack. Hydronium becomes 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.
Move the electrons
The first alcohol attacks the carbonyl carbon. Its oxygen gains a bond 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.
Move the electrons
Water removes a proton from the incoming alcohol oxygen. This gives a neutral 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
Add a proton to the OH group on the former carbonyl carbon. It can now 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.
Move the electrons
The ether oxygen forms a π bond to carbon as the original carbonyl oxygen leaves in water.
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 second alcohol attacks carbon. Move the C=O π electrons onto oxygen so carbon keeps eight electrons.
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
Water removes the proton from the positively charged oxygen. The acetal becomes neutral and hydronium returns.
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 new five-membered ring contains the former carbonyl carbon, both diol oxygens and both diol carbons. Both diol oxygens remain in the cyclic acetal; the original carbonyl oxygen is the water byproduct.
O que você vai praticar
Distinguish intermolecular first capture from intramolecular second capture in a cyclic acetal.
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