Química Orgânica 2 · Éteres e abertura de epóxidos
Resolve oxygen provenance in epoxide hydrolysis
Condições: 2-Methyl-1,2-epoxypropane in dilute aqueous non-nucleophilic acid, represented by hydronium/water with its counterion omitted. Follow water attack at the tertiary carbon and transfer a proton from the oxygen that just added; connectivity only, with no R/S claim.
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Protonate the oxygen
Draw both arrows for the proton transfer. The water formed here can take back a proton later to regenerate hydronium. No halide is added.
Nota: After activation, the two waters are chemically equivalent. One adds to the epoxide; the other removes a proton from the oxygen that just added. Hydronium transfers a proton and becomes water. The acid counterion is not drawn.
As setas curvas
- An oxygen lone pair bonds to the hydronium proton, giving this oxygen a positive charge.
- The O–H bond electrons stay on the water oxygen. Hydronium becomes water.
Continue hydrolysis
Keep both incoming water hydrogens until solvent deprotonation. No free tertiary carbocation is formed; acid-opening regioselectivity depends on substrate, and primary/secondary epoxides can behave differently or give mixtures.
As setas curvas
- Water attacks the tertiary carbon opposite the breaking ring C–O bond; developing positive charge favors this site for this substrate.
- The ring bond pair returns to oxygen in the same event, preserving the carbon octet.
Water takes back a proton
Water removes a proton from the product. The product becomes neutral and water becomes hydronium.
As setas curvas
- The water oxygen takes a proton.
- The O–H bond electrons return to the positively charged oxygen, making it neutral.
Products
HOCH₂C(OH)(CH₃)₂ retains the ring oxygen bonded to CH₂ and the incoming water oxygen bonded to the tertiary carbon. Solvent water becomes hydronium after accepting a proton from the oxygen that just added. All three oxygen atoms, both methyl substituents, and every explicit hydrogen remain; net charge is +1 throughout.
O que você vai praticar
Complete water attack and acid regeneration while distinguishing the two final alcohol oxygens.
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