All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzenebecause of thedeactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for the nitration of benzene and nitrobenzeneshowthat the electron-withdrawing nitro group destabilizes the carbocation intermediate and increases the transition state energy. The higher activation energy barrier for nitrobenzene, compared to that for benzene,makes the reactionslower. Whilemeta-directing groups deactivatethe ring at all positions,deactivation at the ortho and para positions is stronger, resulting inmeta-substituted products.

Tags
Meta directingDeactivatingNitro GroupElectrophilic Aromatic SubstitutionCarbocationActivation EnergyMeta substitution

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18.16 : meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H

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18.1 : Espectroscopía de RMN de derivados del benceno

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18.2 : Reacciones en la posición bencílica: oxidación y reducción

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18.3 : Reacciones en la posición bencílica: halogenación

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18.4 : Sustitución aromática electrofílica: descripción general

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18.5 : Sustitución aromática electrofílica: cloración y bromación del benceno

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18.6 : Sustitución aromática electrofílica: fluoración y yodación del benceno

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18.7 : Sustitución aromática electrofílica: nitración del benceno

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18.9 : Sustitución aromática electrofílica: Friedel-Crafts alquilación de benceno

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18.10 : Sustitución aromática electrofílica: acilación de benceno de Friedel-Crafts

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18.11 : Limitaciones de las reacciones de Friedel-Crafts

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18.12 : Efecto Directivo de los Sustituyentes: Grupos Orto-Para-Directores

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18.13 : Efecto Directivo de los Sustituyentes: Grupos Meta-Directores

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18.14 : Activadores orto-para-direccionamientos: –CH3, –OH, –⁠NH2, –OCH3

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