Textbook Question
Despite having only sp2-hybridized carbons and having 10 electrons (4n + 2) , the annulene shown is not aromatic. Why?
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Ch. 23 - Benzene I: Aromatic Stability and Substitution 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. 23 - Benzene I: Aromatic Stability and Substitution ReactionsProblem 62c
Mullins 1st EditionCh. 23 - Benzene I: Aromatic Stability and Substitution ReactionsProblem 62cChapter 22, Problem 62c
Use a Frost circle diagram to construct the molecular orbital diagram for the molecules shown. Would you expect them to be aromatic or antiaromatic?
(c) 
Verified step by step guidance1
Identify the molecule: The image shows a cycloheptatrienyl cation, which is a seven-membered ring with three conjugated double bonds and a positive charge.
Determine the number of π electrons: Count the π electrons in the conjugated system. Each double bond contributes two π electrons, so there are 6 π electrons in total.
Apply Hückel's rule: For a molecule to be aromatic, it must have (4n + 2) π electrons, where n is a non-negative integer. Check if 6 π electrons fit this rule.
Construct the Frost circle: Draw a circle and inscribe a polygon with the same number of vertices as the ring (7 in this case). The vertices represent the energy levels of the molecular orbitals.
Analyze the molecular orbital diagram: Fill the molecular orbitals with the 6 π electrons starting from the lowest energy level. Determine if all electrons are paired and if the system is aromatic or antiaromatic based on the electron configuration.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Molecular Orbital Theory
Molecular Orbital Theory describes how atomic orbitals combine to form molecular orbitals, which can be occupied by electrons. In this context, the theory helps predict the stability and reactivity of molecules by analyzing the energy levels and occupancy of these orbitals. For aromatic compounds, the presence of a fully filled set of bonding molecular orbitals contributes to their stability.
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Aromaticity
Aromaticity refers to a property of cyclic, planar molecules with a ring of resonance bonds that leads to enhanced stability. A compound is considered aromatic if it follows Hückel's rule, which states that it must have 4n + 2 π electrons (where n is a non-negative integer). This stability arises from the delocalization of π electrons across the ring structure, contributing to unique chemical properties.
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Anti-Aromaticity
Anti-aromaticity is a concept that describes cyclic compounds that have 4n π electrons, leading to instability. Unlike aromatic compounds, anti-aromatic compounds are less stable due to the presence of electron repulsion and lack of resonance stabilization. This instability often results in higher reactivity compared to non-aromatic compounds, making the distinction between aromatic and anti-aromatic crucial in organic chemistry.
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Related Practice
Textbook Question
Using a Frost circle, a student drew the molecular orbital picture shown for the cyclopentadienyl anion, determining it to be antiaromatic. Do you agree with this conclusion? Why or why not?
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Textbook Question
Use a Frost circle diagram to construct the molecular orbital diagram for the molecules shown. Would you expect them to be aromatic or antiaromatic?
(a)
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Textbook Question
In Section 17.7.4, we studied the acid-catalyzed hydrolysis of acetals. The acetal shown here resists hydrolysis by the mechanism in Figure 17.63. Why? [Draw the intermediates as if the reaction would occur, then analyze the intermediates for any problems.]
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Textbook Question
Use a Frost circle diagram to construct the molecular orbital diagram for the molecules shown. Would you expect them to be aromatic or antiaromatic?
(b)
1
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