Química Orgánica 1 · Reacciones de alquenos y alquinos: repaso para el examen
Ozonolysis of cyclopentene to pentanedial
Condiciones: O3, CH2Cl2, −78 °C; then Me2S
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 7 pasos escritos
Ozone adds across the ring alkene
Ozone bonds both ends to the two alkene carbons in one concerted step, giving a bicyclic molozonide.
Las flechas curvas
- A lone pair on the negative end oxygen bonds to one alkene carbon.
- The π pair bonds the other alkene carbon to the far end oxygen.
- The O=O π pair moves onto the central oxygen.
The molozonide fragments
The C–C bond and one O–O bond break. Because both carbons were in the same ring, the aldehyde and the carbonyl oxide stay joined in one five-carbon chain.
Las flechas curvas
- The C–C bond pair becomes the aldehyde C=O π bond.
- The O–O bond breaks onto the middle oxygen.
- An oxygen lone pair forms the C=O⁺ π bond of the carbonyl oxide.
Why one product?
The alkene was inside a ring.
Ring closure to the ozonide
The carbonyl oxide oxygen adds to the aldehyde carbon in the same chain, and the aldehyde oxygen bonds to the carbonyl-oxide carbon, giving a bicyclic ozonide.
Las flechas curvas
- The negative oxygen bonds to the aldehyde carbon.
- The aldehyde C=O π pair bonds its oxygen to the other carbon.
- The C=O⁺ π pair moves onto oxygen, now neutral.
Dimethyl sulfide attacks the O–O bond
A sulfur lone pair of dimethyl sulfide attacks one peroxide oxygen and the O–O bond breaks onto the other oxygen.
Las flechas curvas
- A sulfur lone pair forms the S–O bond.
- The O–O pair moves onto the other oxygen as an alkoxide.
Collapse to the dialdehyde
The alkoxide re-forms a C=O, pushing electrons through the bridging oxygen to form the second C=O and expel DMSO.
Las flechas curvas
- The alkoxide lone pair forms a C=O.
- The ring C–O pair becomes the second C=O π bond.
- The C–O bond to the sulfur-bound oxygen breaks, releasing DMSO.
Pentanedial
The ring has opened to a five-carbon chain with an aldehyde at each end. Dimethyl sulfide is oxidized to DMSO.
Qué vas a practicar
Draw ozone adding to cyclopentene, cleavage of the molozonide, ring closure to the ozonide and its reduction by dimethyl sulfide, giving pentanedial.
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