Ch. 17 - Reactions of Aromatic Compounds

Wade9th EditionOrganic ChemistryISBN: 9780135213728Non è quello che usi tu?Cambia libro di testo

Wade 9th Edition

Ch. 17 - Reactions of Aromatic Compounds

Problema 17-12e

Capitolo 17, Problema 17-12e

Predict the mononitration products of the following compounds.
e. m-cresol (m-methylphenol)

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Identify the structure of m-cresol (m-methylphenol). It is a benzene ring with a hydroxyl (-OH) group at the 1-position and a methyl (-CH₃) group at the 3-position.

Understand the directing effects of the substituents. The hydroxyl (-OH) group is an activating, ortho/para-directing group, while the methyl (-CH₃) group is also an activating, ortho/para-directing group. However, the -OH group is more strongly activating than the -CH₃ group.

Determine the positions on the benzene ring where nitration (introduction of a nitro group, -NO₂) is most likely to occur. The -OH group will direct nitration to the ortho (2, 6) and para (4) positions relative to itself. The -CH₃ group will also direct nitration to its ortho (2, 4) and para (6) positions, but the influence of the -OH group dominates.

Eliminate positions that are sterically hindered or already occupied. The 1-position is occupied by the -OH group, and the 3-position is occupied by the -CH₃ group. This leaves the 2, 4, and 6 positions as potential sites for nitration.

Predict the major product(s) based on the directing effects. The nitro group (-NO₂) will most likely be introduced at the 2-position (ortho to -OH) and the 4-position (para to -OH), as these are the most activated positions. The 6-position (ortho to -OH and para to -CH₃) may also be a minor product due to steric considerations.

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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, such as nitration. The presence of electron-donating or withdrawing groups can significantly affect the position where the electrophile attacks.

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EAS Review

Nitration Reaction

Nitration is a specific type of electrophilic aromatic substitution where a nitro group (NO2) is introduced into an aromatic compound, typically using a mixture of concentrated nitric acid and sulfuric acid. The reaction generates the nitronium ion (NO2+), which acts as the electrophile. Understanding the conditions and mechanisms of nitration is essential for predicting the products formed when nitrating compounds like m-cresol.

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EAS Nitration

Ortho/Para vs. Meta Directing Effects

The directing effects of substituents on an aromatic ring determine the positions where new substituents will be added during electrophilic aromatic substitution. Electron-donating groups, such as the hydroxyl group in m-cresol, typically direct incoming electrophiles to the ortho and para positions, while electron-withdrawing groups direct them to the meta position. Recognizing these patterns is vital for predicting the mononitration products of m-cresol.

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Ortho, Para major products

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