Ch. 16 - Aromatic Compounds

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

Wade 9th Edition

Ch. 16 - Aromatic Compounds

Problem 35m

Chapter 16, Problem 35m

Some of the following compounds show aromatic properties, and others do not.
1. Predict which ones are likely to be aromatic, and explain why they are aromatic.
2. Predict which nitrogen atoms are more basic than water and which are less basic.
(m)

Verified step by step guidance

Step 1: Analyze the structure of the compound provided. The compound is a nitrogen-containing heterocyclic ring with alternating double bonds, which suggests it may exhibit aromatic properties. Aromaticity is determined by the Huckel rule, which states that a compound must have (4n + 2) π-electrons to be aromatic.

Step 2: Count the π-electrons in the ring. Each double bond contributes 2 π-electrons, and the nitrogen atom may contribute a lone pair of electrons if it is part of the conjugated system. Verify if the total number of π-electrons satisfies the Huckel rule.

Step 3: Determine if the nitrogen atom's lone pair is part of the conjugated π-system. If the lone pair is in an sp2 orbital and overlaps with the π-system, it contributes to aromaticity. If the lone pair is in an sp3 orbital, it does not contribute to aromaticity.

Step 4: Evaluate the basicity of the nitrogen atom. Nitrogen atoms are more basic when their lone pair is readily available for protonation. If the lone pair is delocalized in the aromatic π-system, the nitrogen is less basic than water. If the lone pair is localized, the nitrogen is more basic than water.

Step 5: Conclude the aromaticity and basicity of the compound based on the above analysis. If the compound satisfies the Huckel rule and the nitrogen's lone pair contributes to the π-system, it is aromatic. If the nitrogen's lone pair is localized, it is more basic than water; otherwise, it is less basic.

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Key Concepts

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

Aromaticity

Aromaticity refers to the special stability and unique properties of cyclic compounds that follow Hückel's rule, which states that a compound must have (4n + 2) π electrons, where n is a non-negative integer. Aromatic compounds are typically planar, fully conjugated, and exhibit resonance, leading to lower reactivity compared to non-aromatic compounds. Common examples include benzene and pyridine.

Basicity of Nitrogen

The basicity of nitrogen atoms in organic compounds is influenced by their hybridization and the presence of electron-donating or withdrawing groups. Nitrogen in sp3 hybridization (like in amines) is generally more basic than in sp2 (like in pyridine) due to the availability of the lone pair for protonation. The basicity can also be compared to water, where nitrogen atoms that can stabilize the positive charge after protonation are considered more basic.

Heterocycles

Heterocycles are cyclic compounds that contain at least one atom other than carbon in the ring, such as nitrogen, oxygen, or sulfur. The presence of heteroatoms can significantly affect the chemical properties, including aromaticity and basicity. For instance, nitrogen in a heterocyclic aromatic compound can participate in resonance, influencing both its stability and its ability to accept protons, thus affecting its basicity.

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Related Practice

Textbook Question

Some of the following compounds show aromatic properties, and others do not.

1. Predict which ones are likely to be aromatic, and explain why they are aromatic.

(n)

(o)

791

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Textbook Question

The benzene ring alters the reactivity of a neighboring group in the benzylic position much as a double bond alters the reactivity of groups in the allylic position.

Benzylic cations, anions, and radicals are all more stable than simple alkyl intermediates.

a. Use resonance forms to show the delocalization (over four carbon atoms) of the positive charge of the benzyl cation.

1387

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Textbook Question

Some of the following compounds show aromatic properties, and others do not.

1. Predict which ones are likely to be aromatic, and explain why they are aromatic.

2. Predict which nitrogen atoms are more basic than water and which are less basic.

(d)

675

views

Textbook Question

Some of the following compounds show aromatic properties, and others do not.

1. Predict which ones are likely to be aromatic, and explain why they are aromatic.

2. Predict which nitrogen atoms are more basic than water and which are less basic.

(e)

484

views

Textbook Question

The benzene ring alters the reactivity of a neighboring group in the benzylic position much as a double bond alters the reactivity of groups in the allylic position.

Benzylic cations, anions, and radicals are all more stable than simple alkyl intermediates.

a. Use resonance forms to show the delocalization (over four carbon atoms) of the negative charge of the benzyl anion.

1280

views

Textbook Question

Some of the following compounds show aromatic properties, and others do not.

1. Predict which ones are likely to be aromatic, and explain why they are aromatic.

2. Predict which nitrogen atoms are more basic than water and which are less basic.

(f)

503

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Some of the following compounds show aromatic properties, and others do not.1. Predict which ones are likely to be aromatic, and explain why they are aromatic.2. Predict which nitrogen atoms are more basic than water and which are less basic.(m)

Verified video answer for a similar problem:

Key Concepts

Aromaticity

Basicity of Nitrogen

Heterocycles

Some of the following compounds show aromatic properties, and others do not.
1. Predict which ones are likely to be aromatic, and explain why they are aromatic.
2. Predict which nitrogen atoms are more basic than water and which are less basic.
(m)