Electron-releasing groups like –OCH₃, –CH₃ increase the basic strength of substituted aniline, while electron-withdrawing groups like –NO₂, –SO₃H, –COOH, –X decrease it. This observation highlights the role of substituents in influencing the basic nature of aromatic amines.
How do electron-releasing and electron-withdrawing groups affect the basic strength of substituted aniline, and what is the observed impact of groups like –OCH₃ and –NO₂?
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Electron-releasing groups (ERG) enhance the basic strength of substituted aniline by donating electron density to the nitrogen lone pair. Conversely, electron-withdrawing groups (EWG) decrease basicity by withdrawing electron density. In substituted anilines, groups like –OCH₃ (methoxy, an ERG) increase basicity, while –NO₂ (nitro, an EWG) decreases it. Methoxy donates electron density to the ring, making the lone pair more available. Nitro withdraws electron density, reducing the nucleophilicity of the nitrogen lone pair. The impact of these groups on basic strength is a result of their electronic effects, influencing the availability of the lone pair on nitrogen.