Química Orgánica 2 · Sustitución electrofílica aromática
Iodobenzene from benzene with I₂ and HNO₃
Condiciones: I2, HNO3 (oxidant)
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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 6 pasos escritos
The ring attacks the iodine cation carrier
I₂ itself is too weak an electrophile for benzene, so nitric acid oxidizes it to an I⁺ carrier, drawn here as protonated hypoiodous acid (H₂O–I⁺). In the slow step a ring π pair bonds to iodine, water leaves, and aromaticity is lost.
Las flechas curvas
- The ring π pair at the carbon bearing the drawn hydrogen forms the new C–I bond; the neighboring carbon becomes cationic.
- The I–O bond pair stays on oxygen, which leaves as neutral water.
Delocalize the charge to the para carbon
The positive charge of the arenium ion is shared over the two carbons ortho and the carbon para to the new C–I bond.
Las flechas curvas
- The neighboring ring π pair shifts toward the cationic carbon, moving the positive charge to the carbon para to the new bond.
Return the charge beside the sp³ carbon
The arenium ion is one hybrid; redraw the contributor with the positive charge back on the carbon next to the sp³ C–H. That contributor shows which π bond the C–H electrons will re-form in the deprotonation.
Las flechas curvas
- The π pair shifts back toward the para carbon, leaving the positive charge on the ortho carbon next to the sp³ C–H.
Why an oxidant?
Iodination is the one halogenation where the halogen must be oxidized first; the reaction is otherwise uphill and the HI formed would reduce the product back.
Water removes the ring proton
Water (from the aqueous nitric acid, assumed base) removes the proton from the sp³ carbon bearing iodine. The C–H electrons restore the aromatic ring.
Las flechas curvas
- A water lone pair takes the ring proton, forming hydronium.
- The C–H bond electrons form the ring π bond to the neighboring cationic carbon, restoring aromaticity.
Iodobenzene
Iodine has replaced a ring hydrogen to give iodobenzene, and the proton ends up on water as hydronium.
Qué vas a practicar
Draw iodination of benzene by the I⁺ electrophile made from I₂ and HNO₃: ring attack, arenium contributors, and deprotonation by water to give iodobenzene.
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