Textbook Question
Would you expect the following molecules to absorb in the UV–visible region of the electromagnetic spectrum?
(a)
(b)
(c)
(d)
(e)
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Ch. 21 - Conjugated Systems I: Stability and Addition Reactions
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
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Mullins 1st EditionCh. 21 - Conjugated Systems I: Stability and Addition ReactionsProblem 53
Mullins 1st EditionCh. 21 - Conjugated Systems I: Stability and Addition ReactionsProblem 53Chapter 20, Problem 53
Draw the molecular orbital picture of octa-1,3,5,7-tetraene, indicating which is the HOMO and which is the LUMO.
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Identify the structure of octa-1,3,5,7-tetraene, which is a linear conjugated system with eight carbon atoms and alternating double bonds.
Determine the number of π electrons in the molecule. Each double bond contributes two π electrons, so for four double bonds, there are 8 π electrons.
Construct the molecular orbital diagram for a linear conjugated system with eight π electrons. This involves creating a series of π molecular orbitals, each with increasing energy levels.
Fill the molecular orbitals with the 8 π electrons, starting from the lowest energy orbital and following Hund's rule and the Pauli exclusion principle.
Identify the Highest Occupied Molecular Orbital (HOMO) as the highest energy orbital that contains electrons, and the Lowest Unoccupied Molecular Orbital (LUMO) as the next higher energy orbital that does not contain electrons.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Molecular Orbitals
Molecular orbitals (MOs) are formed by the combination of atomic orbitals when atoms bond together. In conjugated systems like octa-1,3,5,7-tetraene, MOs can be classified as bonding, non-bonding, or antibonding. The arrangement and energy levels of these orbitals are crucial for understanding the electronic structure and reactivity of the molecule.
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HOMO and LUMO
The Highest Occupied Molecular Orbital (HOMO) is the molecular orbital that contains the highest energy electrons, while the Lowest Unoccupied Molecular Orbital (LUMO) is the lowest energy orbital that is unoccupied. The energy difference between the HOMO and LUMO is significant for predicting the molecule's reactivity and stability, as it influences how the molecule interacts with light and other chemical species.
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Conjugation
Conjugation refers to the overlap of p-orbitals across adjacent double bonds, allowing for delocalization of π electrons. In octa-1,3,5,7-tetraene, this delocalization stabilizes the molecule and affects its electronic properties. Understanding conjugation is essential for drawing accurate molecular orbital diagrams and predicting the behavior of the molecule in various chemical contexts.
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Related Practice
Textbook Question
The dye alizarin normally forms an orange solution when dissolved. However, if KOEt is added to the solution, it turns blue very rapidly. Rationalize this result.
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Textbook Question
Which of the following reactions would you expect to be faster/more favorable in each pair? Why?
(c)
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Textbook Question
Which of the following reactions would you expect to be faster/more favorable in each pair? Why?
(b)
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Textbook Question
On a per alkene basis, which would have the more negative heat of hydrogenation?
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Textbook Question
How many 𝝅 electrons are involved in the conjugated system for each of the following molecules?
(a)
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