Química Orgánica 2 · Sustitución de acilo y elección del derivado
γ-Butyrolactone from 4-hydroxybutanoic acid
Condiciones: H⁺ (cat.)
Dibuja este problema tú mismo
Arrastra desde los electrones que se mueven hasta donde van, o toca uno y luego el otro. Cada flecha se revisa; Pista te ayuda cuando te atascas. No necesitas cuenta.
El mecanismo, paso a paso
Siguiente reproduce las flechas curvas de cada paso y las explica. Los pasos escritos están abajo.
Leer los 8 pasos escritos
Activate the carbonyl
The acid catalyst (drawn as hydronium) protonates the carbonyl oxygen of the acid. The protonated carbonyl carbon is now electrophilic enough for a neutral alcohol to attack.
Las flechas curvas
- The carbonyl oxygen lone pair takes a proton from hydronium.
- The O–H bond pair stays on the water oxygen.
The hydroxyl closes the ring
The chain OH is four carbons away, so its oxygen reaches the activated carbonyl carbon and forms a five-membered ring; the C=O π pair moves onto oxygen.
Las flechas curvas
- The hydroxyl oxygen lone pair attacks the carbonyl carbon.
- The C=O π pair moves onto the protonated oxygen, neutralising it.
Ring size
Count the atoms in the new ring.
Remove the ring oxonium proton
Water takes the proton from the positively charged ring oxygen, giving a neutral tetrahedral intermediate.
Las flechas curvas
- Water takes the proton from the ring oxonium oxygen.
- The O–H pair stays on the ring oxygen.
Protonate the leaving OH
Hydronium protonates one OH of the tetrahedral intermediate, turning it into water, a good leaving group.
Las flechas curvas
- An OH lone pair takes a proton from hydronium.
- The O–H bond pair returns to water.
Lose water
The other OH lone pair forms a C=O π bond and pushes water out, giving the protonated lactone.
Las flechas curvas
- An oxygen lone pair forms the C=O π bond.
- The C–O bond breaks and water leaves.
Release the lactone
Water removes the proton on the carbonyl oxygen, giving the neutral lactone and regenerating the acid catalyst.
Las flechas curvas
- Water takes the carbonyl O–H proton.
- The O–H pair becomes a lone pair on the carbonyl oxygen.
γ-Butyrolactone
γ-Butyrolactone and water form; hydronium is regenerated, so the acid is truly catalytic. The ring oxygen comes from the alcohol, while the lost water carries an oxygen from the acid.
Qué vas a practicar
Draw the acid-catalysed ring closure of 4-hydroxybutanoic acid to γ-butyrolactone, with every proton transfer.
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