Química Orgánica 2 · Repaso de sustitución aromática para el examen
Nitration of 1,3-dimethoxybenzene to 2,4-dimethoxy-1-nitrobenzene
Condiciones: HNO3, AcOH
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
Nitric acid protonates a second nitric acid
Without sulfuric acid, nitric acid itself is the strongest acid present: one molecule protonates the hydroxyl oxygen of another (acetic acid is only the solvent).
Las flechas curvas
- The hydroxyl oxygen of one nitric acid takes the proton of the other.
- The O–H pair stays on oxygen, giving nitrate.
Water leaves to give the nitronium ion
Water leaves from the protonated nitric acid and the anionic oxygen forms a second N=O bond, giving a small amount of nitronium ion, enough for this very reactive ring.
Las flechas curvas
- The N–O pair leaves with oxygen as water.
- An oxygen lone pair forms the second N=O bond.
C4 attacks nitronium
C4 is ortho to one methoxy group and para to the other, so both activate it. Its ring π pair forms the C–N bond and the positive charge lands on the carbon bearing a methoxy group.
Las flechas curvas
- The ring π pair forms the C–N bond at C4.
- An N=O π pair moves onto oxygen.
The adjacent methoxy oxygen shares the charge
An oxygen lone pair forms a C=O⁺ π bond so every atom has an octet; the second methoxy group can stabilise the same cation through the ring as well.
Las flechas curvas
- An oxygen lone pair forms a π bond to the cationic carbon.
Where both groups agree
C4 (and the equivalent C6) is activated by both methoxy groups and is less crowded than C2.
Nitrate removes the ring proton
Nitrate takes the proton from the sp³ carbon; the C–H pair re-forms the ring π bond and the C=O⁺ π pair returns to oxygen.
Las flechas curvas
- A nitrate oxygen takes the ring proton.
- The C–H pair re-forms the ring π bond.
- The C=O⁺ π pair returns to oxygen.
2,4-Dimethoxy-1-nitrobenzene
2,4-Dimethoxy-1-nitrobenzene forms and nitric acid is regenerated.
Qué vas a practicar
Draw nitronium formation from nitric acid, attack at C4 of 1,3-dimethoxybenzene with methoxy stabilisation, and loss of the ring proton.
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