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Ch. 18 - Reactions of Benzene and Substituted Benzenes
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoBruice 8th EditionCh. 18 - Reactions of Benzene and Substituted BenzenesProblema 39b
Capitolo 18, Problema 39b

b. Rank the same compounds from greatest tendency to least tendency to undergo electrophilic aromatic substitution.
chlorobenzene, 1-chloro-2,4-dinitrobenzene, p-chloronitrobenzene

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1
Identify the compounds provided in the problem and determine the substituents attached to the aromatic ring. Substituents can either activate or deactivate the ring toward electrophilic aromatic substitution (EAS). Activating groups increase the tendency for EAS, while deactivating groups decrease it.
Classify each substituent as either an electron-donating group (EDG) or an electron-withdrawing group (EWG). EDGs, such as -OH, -OCH3, and alkyl groups, stabilize the intermediate carbocation formed during EAS, making the reaction more favorable. EWGs, such as -NO2, -CF3, and -COOH, destabilize the intermediate carbocation, making the reaction less favorable.
Consider the resonance and inductive effects of each substituent. Resonance effects occur when the substituent can donate or withdraw electrons through π-bond interactions, while inductive effects involve electron withdrawal or donation through σ-bonds. Substituents with strong resonance-donating effects (e.g., -OH, -NH2) are typically stronger activators than those with only inductive effects.
Rank the compounds based on the overall activating or deactivating influence of their substituents. Compounds with strong activating groups will have the greatest tendency to undergo EAS, while those with strong deactivating groups will have the least tendency.
If multiple substituents are present on a single aromatic ring, evaluate their combined effects. Activating groups generally dominate over deactivating groups, but the position of the substituents (ortho, meta, or para) can also influence the reactivity. Use this information to finalize the ranking of the compounds.

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Electrophilic Aromatic Substitution (EAS)

Electrophilic Aromatic Substitution is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. This reaction is crucial for modifying aromatic compounds and is influenced by the nature of substituents already present on the ring, which can either activate or deactivate the ring towards further substitution.
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EAS Review

Activating and Deactivating Groups

Substituents on an aromatic ring can be classified as activating or deactivating based on their electronic effects. Activating groups, such as -OH or -NH2, increase the electron density of the ring, making it more reactive towards electrophiles. In contrast, deactivating groups, like -NO2 or -CF3, withdraw electron density, reducing the ring's reactivity and influencing the position of substitution.
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Activating and deactivating groups

Ortho/Para vs. Meta Directing

The position of substitution in electrophilic aromatic substitution is also determined by whether the substituents are ortho/para or meta directing. Activating groups typically direct incoming electrophiles to the ortho and para positions, while deactivating groups usually direct them to the meta position. Understanding these directing effects is essential for predicting the outcome of EAS reactions.
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Ortho, Para major products
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