Textbook Question
Which species in each of the pairs in Problem 80 is the stronger base?
a.
b.
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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: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- 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 Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 86a
Bruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 86aChapter 9, Problem 86a
Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:
a. How many MOs does the compound have?
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Count the number of conjugated π-electrons in the molecule. In 1,3,5,7-octatetraene, there are four double bonds, each contributing two π-electrons, for a total of 8 π-electrons.
Determine the number of atomic p orbitals involved in the conjugated π-system. Each carbon atom in the conjugated system contributes one p orbital. Since there are 8 carbons in the conjugated system, there are 8 p orbitals.
Recall that the number of molecular orbitals (MOs) formed in a conjugated π-system is equal to the number of atomic p orbitals involved. Therefore, 8 MOs will be formed.
Understand that these 8 MOs will include bonding, non-bonding, and anti-bonding orbitals, arranged in increasing energy levels based on the overlap of the p orbitals.
Conclude that the compound 1,3,5,7-octatetraene has 8 molecular orbitals (MOs) in its conjugated π-system.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Molecular Orbitals (MOs)
Molecular orbitals are formed by the linear combination of atomic orbitals (LCAO) when atoms bond together. In a molecule, these orbitals can be occupied by electrons and are classified as bonding, antibonding, or non-bonding. The number of MOs corresponds to the number of atomic orbitals that combine, which is crucial for understanding the electronic structure of the molecule.
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Conjugation
Conjugation refers to the overlap of p-orbitals across adjacent double bonds, allowing for delocalization of electrons. In 1,3,5,7-octatetraene, the alternating double bonds create a system of conjugated MOs, which lowers the energy of the system and increases stability. This concept is essential for determining the number and type of MOs in conjugated systems.
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Counting Molecular Orbitals
The total number of molecular orbitals in a molecule is equal to the number of atomic orbitals that combine to form them. For 1,3,5,7-octatetraene, which has eight carbon atoms, each contributing one p-orbital, the total number of MOs is equal to the number of contributing atomic orbitals. This principle is fundamental for calculating the MOs in any given molecule.
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Related Practice
Textbook Question
Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:
d. Which MO is the HOMO and which is the LUMO in the ground state?
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Textbook Question
Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:
c. Which MOs are symmetric, and which are antisymmetric?
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Textbook Question
Rank the indicated hydrogen in the following compounds from most acidic to least acidic:
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Textbook Question
Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:
b. Which are the bonding MOs, and which are the antibonding MOs?
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Textbook Question
Purine is a heterocyclic compound with four nitrogen atoms.
a. Which nitrogen is most apt to be protonated?
b. Which nitrogen is least apt to be protonated?
1
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