Química Orgânica 1 · Reações radicalares e seletividade
Grow peroxides in an old bottle of ether
Condições: Diethyl ether stored in contact with air. A 1-ethoxyethylperoxyl radical, formed in an earlier cycle, is the chain carrier. Ground-state O₂ is drawn in the common textbook diradical form •O–O•. Follow one propagation cycle; initiation, termination and later peroxide chemistry are outside this task.
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 4 passos escritos
Abstract an α-hydrogen with the peroxyl radical
The peroxyl radical becomes a hydroperoxide (ROOH). Peroxyl radicals are fairly unreactive, so they abstract only relatively weak C–H bonds, such as those next to an ether oxygen.
Nota: The four CH₂ hydrogens next to oxygen are equivalent.
As setas curvas
- The unpaired electron on the terminal peroxyl oxygen supplies one electron of the new O–H bond.
- One electron of the α C–H bond completes the O–H bond.
- The other C–H electron stays on the α carbon.
Why the carbon next to oxygen?
Autoxidation is selective for the α carbon of ethers, which is why peroxides build up in stored ether.
Capture O₂ at the carbon radical
Carbon radicals combine with O₂ at nearly every encounter. The other oxygen keeps its unpaired electron, so a new peroxyl radical forms.
As setas curvas
- The unpaired electron on the α carbon supplies one electron of the new C–O bond.
- One unpaired electron of O₂ completes the C–O bond.
Ether hydroperoxide and a new peroxyl carrier
The old carrier is now 1-ethoxyethyl hydroperoxide, with an O–H bond and two lone pairs on each oxygen. The substrate has become a new 1-ethoxyethylperoxyl radical with the unpaired electron on its terminal oxygen: the same kind of carrier that started the cycle. The chain therefore keeps converting ether and O₂ into hydroperoxide, which is why old ether can hold dangerous peroxide levels.
O que você vai praticar
Close an autoxidation chain in which a peroxyl radical abstracts an α-hydrogen and the resulting carbon radical captures O₂, regenerating the same kind of peroxyl carrier.
Você acabou de desenhar cada seta deste problema.
Cada um dos 5349 problemas de Orgânica 1 e 2 funciona assim: feedback em cada seta, dicas quando você travar e um modo prova sem dicas. Grátis com uma conta, sem cartão.
Travou na sua própria lição?
Tire uma foto: o primeiro scan é grátis, sem cadastro
Você escaneia toda semana? Scan Standard: por cerca de problemas