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18.18 : Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)

Nucleophilic substitution in aromatic compounds is feasible in substrates bearing strong electron-withdrawing substituents positioned ortho or para to the leaving group. The reaction proceeds via two steps: the addition of the nucleophile and the elimination of the leaving group.

The reaction beginswith an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between the delocalized electron pair and the electron-withdrawing group further stabilizes the intermediate through the formation of Meisenheimer complexes. Finally, the electron-withdrawing group releases the electron back into the ring, facilitatingthe departure of the leaving group and restoringaromaticity.

Tags
Nucleophilic Aromatic SubstitutionSNArAddition eliminationElectron withdrawing SubstituentsMeisenheimer ComplexAromaticity

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18.18 : Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)

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18.1 : NMR Spectroscopy of Benzene Derivatives

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18.2 : Reactions at the Benzylic Position: Oxidation and Reduction

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18.3 : Reactions at the Benzylic Position: Halogenation

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18.4 : Electrophilic Aromatic Substitution: Overview

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18.5 : Electrophilic Aromatic Substitution: Chlorination and Bromination of Benzene

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18.6 : Electrophilic Aromatic Substitution: Fluorination and Iodination of Benzene

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18.7 : Electrophilic Aromatic Substitution: Nitration of Benzene

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18.8 : Electrophilic Aromatic Substitution: Sulfonation of Benzene

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18.9 : Electrophilic Aromatic Substitution: Friedel–Crafts Alkylation of Benzene

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18.10 : Electrophilic Aromatic Substitution: Friedel–Crafts Acylation of Benzene

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18.11 : Limitations of Friedel–Crafts Reactions

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18.12 : Directing Effect of Substituents: ortho–para-Directing Groups

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18.13 : Directing Effect of Substituents: meta-Directing Groups

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18.14 : ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3

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