Ch. 17 - Reactions of Aromatic Compounds

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch. 17 - Reactions of Aromatic Compounds

Problem 19a

Chapter 17, Problem 19a

Show how you would synthesize the following aromatic derivatives from benzene.
a. p-tert-butylnitrobenzene

Verified step by step guidance

Step 1: Begin with benzene as the starting material. Benzene is an aromatic compound with a planar ring structure and alternating double bonds.

Step 2: Introduce the tert-butyl group onto the benzene ring through Friedel-Crafts alkylation. Use tert-butyl chloride (C(CH₃)₃Cl) as the alkylating agent and aluminum chloride (AlCl₃) as the catalyst. This reaction will yield tert-butylbenzene.

Step 3: Nitrate the tert-butylbenzene to introduce the nitro group (-NO₂). Perform an electrophilic aromatic substitution reaction using a nitrating mixture of concentrated sulfuric acid (H₂SO₄) and concentrated nitric acid (HNO₃). This reaction will add the nitro group to the para position relative to the tert-butyl group due to steric hindrance and electronic effects.

Step 4: Carefully control the reaction conditions to ensure selective nitration at the para position. The tert-butyl group is an electron-donating group, which directs the incoming nitro group to the para position.

Step 5: Purify the product, p-tert-butylnitrobenzene, using techniques such as recrystallization or chromatography to isolate the desired compound from any side products or unreacted starting materials.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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 process is crucial for synthesizing various aromatic compounds, as it allows for the introduction of different functional groups onto the benzene ring. Understanding the mechanism of EAS, including the role of catalysts and the stability of intermediates, is essential for predicting the outcomes of reactions involving aromatic compounds.

Activating and Deactivating Groups

In the context of EAS, substituents on the aromatic ring can either activate or deactivate the ring towards further substitution. Activating groups, such as alkyl groups, increase the electron density of the ring, making it more reactive towards electrophiles. Conversely, deactivating groups, like nitro groups, withdraw electron density and make the ring less reactive. Recognizing how these groups influence the position and rate of substitution is vital for successful synthesis.

Ortho/Para vs. Meta Directing Effects

The directing effects of substituents on an aromatic ring determine where new substituents will be added during EAS. Ortho and para directing groups favor substitution at the 2 and 4 positions relative to themselves, while meta directing groups favor substitution at the 3 position. Understanding these patterns is essential for predicting the structure of the final product, such as p-tert-butylnitrobenzene, and for planning the synthetic route effectively.

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Related Practice

Textbook Question

Show how you would synthesize the following aromatic derivatives from benzene.

c. p-chlorotoluene

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Textbook Question

Which reactions will produce the desired product in good yield? You may assume that aluminum chloride is added as a catalyst in each case. For the reactions that will not give a good yield of the desired product, predict the major products.

(e) Reagents: toluene + HNO₃, H₂SO₄, heat

Desired Product: 2,4,6-trinitrotoluene (TNT)

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Textbook Question

Predict the mononitration products of the following compounds.

e. m-cresol (m-methylphenol)

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Textbook Question

Show how you would use the Friedel–Crafts acylation, Clemmensen reduction, and/or Gatterman–Koch synthesis to prepare the following compounds:

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