Química Orgânica 2 · Condensação de Claisen e adição conjugada
Dieckmann condensation — adipate cyclization through workup
Condições: Diethyl adipate and sodium ethoxide in dilute ethanol, then separately dilute aqueous HCl (drawn as hydronium). Follow the five-membered intramolecular condensation branch. Counterions omitted; stereochemistry is unspecified.
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 6 passos escritos
Remove an alpha hydrogen
Follow the specified donor site. The carbon-centered enolate is a resonance contributor, not a claim of a localized free carbanion. Initial enolate formation need not be quantitative; later product trapping drives this sequence. An ester α C–H (pKa ≈ 25) is far less acidic than ethanol (pKa ≈ 16), so ethoxide keeps only a tiny enolate fraction (K ≈ 10⁻⁹) at any moment. Ethoxide matches the ethyl esters, so any acyl substitution by the base simply regenerates the same ester.
Nota: The two ends of the initial diester are chemically equivalent. The two drawn alpha hydrogens are equivalent.
As setas curvas
- The base uses a lone pair to bond to the drawn hydrogen.
- The bond to hydrogen breaks, leaving its electrons on the atom that lost H.
Connect the donor and acceptor
The tethered enolate closes onto the distal ester carbonyl, making a five-membered ring while keeping the donor ester intact.
Nota: The two ends of the initial diester are chemically equivalent.
As setas curvas
- The nucleophile uses a lone pair to form the new σ bond.
- The C=O π electrons move to oxygen so carbon keeps eight electrons.
Resolve the acyl-addition intermediate
Carbonyl restoration expels ethoxide. The beta-dicarbonyl product still has a hydrogen between the two carbonyls, allowing deprotonation to drive the reaction forward.
As setas curvas
- An oxygen lone pair forms the C=O π bond again.
- The leaving group takes the electrons from the bond that breaks.
Remove an alpha hydrogen
The hydrogen between the two carbonyl groups is more acidic than the original donor alpha hydrogen. Its removal traps the condensation product as a stabilized anion and protonates the leaving alkoxide. With pKa about 11 or lower for this β-dicarbonyl C–H against 16 for ethanol, the deprotonation is favorable by roughly 10⁵ and pulls the reversible earlier steps toward product; that is why a full equivalent of alkoxide is used.
As setas curvas
- The base uses a lone pair to bond to the drawn hydrogen.
- The bond to hydrogen breaks, leaving its electrons on the atom that lost H.
Separate acidic workup
Only now is hydronium introduced for a separate workup. Protonate the carbon-centered contributor to display the neutral keto tautomer; subsequent tautomer ratios are not part of the assignment. Hydronium (pKa ≈ −1.7) is a far stronger acid than the β-dicarbonyl product (pKa about 11), so this protonation goes to completion.
Nota: Hydronium is now introduced for the workup.
As setas curvas
- The base uses a lone pair to bond to the drawn hydrogen.
- The bond to hydrogen breaks, leaving its electrons on the atom that lost H.
Products
One new C–C bond and a restored acceptor carbonyl create the beta-dicarbonyl framework. The two original donor hydrogens moved to two ethanol molecules; the final alpha hydrogen comes from workup. The neutral keto tautomer is displayed without claiming it is the only solution tautomer. All counterions are consistently outside the reacting model.
O que você vai praticar
Count the ring atoms in an intramolecular Claisen reaction and include the driving product deprotonation and workup.
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