Química Orgánica 2 · Efectos de los sustituyentes y orientación
Nitration of naphthalene at C1
Condiciones: HNO3, H2SO4
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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.
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Naphthalene attacks the nitronium ion at C1
The nitronium ion, O=N+=O, is formed from nitric acid by sulfuric acid (protonation of the N–OH, loss of water); it is drawn here already formed. The C1=C2 π pair of naphthalene forms the C–N bond at C1, leaving a cation at C2.
Las flechas curvas
- The ring π pair forms the new C–N bond to the nitronium nitrogen.
- One N=O π pair moves onto oxygen so nitrogen does not exceed four bonds; the new group is a neutral nitro group.
Move the charge to C4, keeping a benzene ring
The cation is allylic within the attacked ring: it is shared by C2 and C4 while the second ring keeps an intact aromatic sextet. Attack at C1 has two such contributors; attack at C2 has only one, which is why C1 (α) substitution is faster.
Las flechas curvas
- The C3=C4 π pair shifts toward the cation, moving the positive charge to C4 while the other ring stays a benzene ring.
Why naphthalene reacts at C1
Count σ-complex contributors that keep a benzene ring intact.
Hydrogen sulfate removes the ring proton
Hydrogen sulfate, the strongest base in mixed acid, removes the hydrogen on the sp3 ring carbon; the electrons flow back around the ring and aromaticity is restored.
Las flechas curvas
- A hydrogen sulfate oxygen lone pair takes the hydrogen on the sp3 ring carbon.
- The C–H bond pair becomes a ring π bond, starting to restore the aromatic sextet.
- A ring π pair shifts one bond along to make room for the new π bond.
1-nitronaphthalene
Nitration gives 1-nitronaphthalene (with a little 2-isomer) and sulfuric acid is regenerated, so it acts as a catalyst.
Qué vas a practicar
Draw nitration of naphthalene at C1 and the σ-complex contributor that keeps the second ring benzenoid.
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