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18.18: orthopara-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3

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Organic Chemistry

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orthopara-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3

18.18: orthopara-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3

All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding intermediates through resonance effects via pi-donation. As a result, the energy of the transition state is lowered for ortho and para intermediates, leading to an accelerated reaction.


Ortho-para Directing Activators CH3 OH NH2 OCH3 Activating Groups Electron Donation Ring Carbons Electron-rich Reactivity Aromatic Ring Electrophilic Substitution Nitration Anisole Benzene Methoxy Group Resonance Effects Pi-donation Transition State

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