Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene

Problem 57a

Chapter 9, Problem 57a

What orbitals contain the electrons represented as lone pairs in the structures of quinoline, indole, imidazole?

Verified step by step guidance

Step 1: Analyze the structures of quinoline, indole, and imidazole. Quinoline contains a nitrogen atom in a pyridine ring fused to a benzene ring. Indole contains a nitrogen atom in a pyrrole ring fused to a benzene ring. Imidazole contains two nitrogen atoms in a five-membered ring.

Step 2: Determine the hybridization of the nitrogen atoms in each structure. In quinoline, the nitrogen atom is sp2 hybridized because it is part of an aromatic system. In indole, the nitrogen atom is sp2 hybridized as it is part of the aromatic pyrrole ring. In imidazole, one nitrogen is sp2 hybridized (part of the aromatic system), and the other nitrogen is sp2 hybridized but has a lone pair not involved in aromaticity.

Step 3: Identify the orbitals containing the lone pairs. For sp2 hybridized nitrogen atoms, the lone pairs are located in sp2 orbitals. In quinoline, the lone pair on nitrogen resides in an sp2 orbital. In indole, the lone pair on nitrogen also resides in an sp2 orbital. In imidazole, the lone pair on the sp2 nitrogen not involved in aromaticity resides in an sp2 orbital.

Step 4: Consider the aromaticity of the systems. The lone pairs in quinoline and indole do not participate in aromaticity and remain localized in sp2 orbitals. In imidazole, one nitrogen contributes its lone pair to the aromatic π-system, while the other nitrogen's lone pair remains localized in an sp2 orbital.

Step 5: Summarize the findings. The lone pairs in quinoline, indole, and imidazole are located in sp2 orbitals. In imidazole, one nitrogen's lone pair contributes to aromaticity, while the other nitrogen's lone pair remains localized.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

10m

Was this helpful?

Key Concepts

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

Lone Pairs

Lone pairs are pairs of valence electrons that are not involved in bonding and are localized on a single atom. In organic molecules, they can influence reactivity, molecular geometry, and polarity. Understanding where these lone pairs are located in a molecule is crucial for predicting its chemical behavior and interactions.

Hybridization

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals that can accommodate bonding and lone pairs. In the context of quinoline, indole, and imidazole, recognizing the hybridization of nitrogen atoms helps identify the orbitals that contain lone pairs. For example, sp2 hybridization typically involves one lone pair in a trigonal planar arrangement.

Molecular Structure and Resonance

The molecular structure of compounds like quinoline, indole, and imidazole can exhibit resonance, where electrons are delocalized over multiple atoms. This delocalization affects the distribution of lone pairs and can stabilize the molecule. Understanding resonance structures is essential for determining the actual electron distribution and the role of lone pairs in these compounds.

Recommended video:

Guided course

03:04

Drawing Resonance Structures

Related Practice

Textbook Question

Refer to the electrostatic potential maps <IMAGE> to answer the following questions:

c. Why is the center of the electrostatic potential map of benzene more red than the center of the electrostatic potential map of pyridine?

1669

views

Textbook Question

What orbital do the lone-pair electrons occupy in each of the following compounds?

1942

views

Textbook Question

Which of the following compounds could be protonated without destroying its aromaticity?

1287

views

Textbook Question

Following the instructions for drawing the energy levels of the molecular orbitals for the compounds shown in [Figure 8.17], draw the energy levels of the molecular orbitals for the cycloheptatrienyl cation. For each compound, show the distribution of the $\pi$ electrons. Which of the compounds are aromatic?

886

views

Textbook Question

What orbitals contain the electrons represented as lone pairs in the structures of purine, and pyrimidine?