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Ch. 17 - Reactions of Aromatic Compounds
Wade - Organic Chemistry 9th Edition
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Tutti i libri di testoWade 9th EditionCh. 17 - Reactions of Aromatic CompoundsProblema 12a,b,c
Capitolo 17, Problema 12a,b,c

Predict the mononitration products of the following compounds.
a. o-nitrotoluene
b. m-chlorotoluene
c. o-bromobenzoic acid

Guida verificata passo dopo passo
1
Step 1: Understand the concept of electrophilic aromatic substitution (EAS), specifically nitration. Nitration involves the introduction of a nitro group (-NO₂) to an aromatic ring using a mixture of concentrated HNO₃ and H₂SO₄. The position of substitution is influenced by the substituents already present on the ring.
Step 2: Analyze the directing effects of the substituents on each compound. Substituents can be either electron-donating (activating) or electron-withdrawing (deactivating), and they can direct incoming groups to ortho, meta, or para positions. For example, methyl (-CH₃) is an electron-donating group and directs to ortho/para positions, while nitro (-NO₂), chloro (-Cl), and carboxylic acid (-COOH) are electron-withdrawing groups and direct to meta positions.
Step 3: For (a) o-nitrotoluene, the nitro group (-NO₂) is a strong electron-withdrawing group and directs substitution to the meta position relative to itself. The methyl group (-CH₃) is an electron-donating group and directs substitution to the ortho/para positions relative to itself. Consider the combined directing effects to predict the most likely nitration product.
Step 4: For (b) m-chlorotoluene, the chlorine atom (-Cl) is an electron-withdrawing group and directs substitution to the meta position relative to itself. The methyl group (-CH₃) directs substitution to the ortho/para positions relative to itself. Evaluate the combined directing effects to determine the nitration product.
Step 5: For (c) o-bromobenzoic acid, the bromine atom (-Br) is a weakly electron-withdrawing group and directs substitution to the ortho/para positions relative to itself. The carboxylic acid group (-COOH) is a strong electron-withdrawing group and directs substitution to the meta position relative to itself. Analyze the combined directing effects to predict the nitration product.

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Electrophilic Aromatic Substitution

Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. This process is crucial for understanding how substituents on the ring influence the reactivity and orientation of further substitutions. The nature of the substituents, whether they are electron-donating or electron-withdrawing, significantly affects the position where the new electrophile will attach.
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EAS Review

Ortho/Para vs. Meta Directing Effects

Substituents on an aromatic ring can direct incoming electrophiles to specific positions based on their electronic effects. Electron-donating groups (like alkyl groups) typically direct substitution to the ortho and para positions, while electron-withdrawing groups (like nitro or carboxylic acid groups) direct substitution to the meta position. Understanding these directing effects is essential for predicting the products of nitration reactions.
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Ortho, Para major products

Nitration Reaction Mechanism

The nitration of aromatic compounds involves the generation of the nitronium ion (NO2+) from a mixture of concentrated nitric acid and sulfuric acid. This ion acts as the electrophile in the EAS mechanism. The reaction proceeds through the formation of a sigma complex, followed by deprotonation to restore aromaticity. Recognizing this mechanism helps in predicting the outcome of nitration on various aromatic substrates.
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EAS Nitration
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