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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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 86e
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 86eChapter 9, Problem 86e
Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:
e. Which MO is the HOMO and which is the LUMO in the excited state?
Verified step by step guidance1
Step 1: Understand the structure of 1,3,5,7-octatetraene. It is a conjugated system with 8 π-electrons distributed across 4 double bonds. The molecular orbitals (MOs) are formed by the combination of the p-orbitals from the conjugated system, resulting in bonding, non-bonding, and anti-bonding MOs.
Step 2: Recall the Aufbau principle for filling molecular orbitals. In the ground state, the π-electrons fill the MOs starting from the lowest energy level (most bonding) to the highest energy level (least bonding or anti-bonding). The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are identified based on this filling.
Step 3: In the excited state, one of the electrons from the HOMO is promoted to the LUMO. This changes the electron configuration of the molecule, and the new HOMO and LUMO must be identified based on the updated electron distribution.
Step 4: Determine the new HOMO in the excited state. After the electron is promoted, the previously occupied HOMO becomes partially or fully unoccupied, and the next lower energy orbital that is still fully occupied becomes the new HOMO.
Step 5: Determine the new LUMO in the excited state. After the electron is promoted, the previously unoccupied LUMO becomes partially or fully occupied, and the next higher energy orbital that is still unoccupied becomes the new LUMO.
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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 combination of atomic orbitals when atoms bond together. They can be classified as bonding, antibonding, or non-bonding orbitals, and they play a crucial role in determining the electronic structure of molecules. In conjugated systems like octatetraene, MOs are filled according to the Aufbau principle, influencing the molecule's reactivity and properties.
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HOMO and LUMO
The Highest Occupied Molecular Orbital (HOMO) is the molecular orbital that contains the highest energy electrons in a ground state molecule, while the Lowest Unoccupied Molecular Orbital (LUMO) is the lowest energy orbital that is unoccupied. The energy gap between the HOMO and LUMO is critical for understanding electronic transitions, such as those occurring during excitation, which can lead to absorption of light and other photophysical processes.
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Excited State
An excited state refers to a condition of a molecule where one or more electrons have absorbed energy and moved to a higher energy level, typically from the HOMO to the LUMO. This transition alters the molecule's electronic configuration and can significantly affect its chemical reactivity and spectral properties. Understanding the excited state is essential for predicting how a molecule will interact with light and other forms of energy.
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Related Practice
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
How could you synthesize the following compound from starting materials containing no more than six carbons?
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Textbook Question
Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:
g. How many nodes does the highest-energy MO of 1,3,5,7-octatetraene have between the nuclei?
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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
Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:
f. What is the relationship between HOMO and LUMO and symmetric and antisymmetric orbitals?
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