Textbook Question
(i) Classify the following molecules as aromatic, nonaromatic, or antiaromatic.
(ii) For aromatic molecules, solve for n in Hückel’s rule. For all other molecules, explain which rule of aromaticity is being broken.
(h)
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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 62a
Mullins 1st EditionCh. 23 - Benzene I: Aromatic Stability and Substitution ReactionsProblem 62aChapter 22, Problem 62a
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) 
Verified step by step guidance1
Identify the molecule: The image shows a square with two double bonds, which is cyclobutadiene.
Draw the Frost circle: Place the polygon (square) inside a circle with one vertex pointing down. The vertices of the polygon represent the energy levels of the molecular orbitals.
Determine the number of π electrons: Cyclobutadiene has 4 π electrons, as each double bond contributes 2 π electrons.
Fill the molecular orbitals: Start filling the molecular orbitals from the lowest energy level upwards, following Hund's rule and the Pauli exclusion principle.
Assess aromaticity: Apply Hückel's rule, which states that a molecule is aromatic if it has (4n + 2) π electrons. Cyclobutadiene has 4 π electrons, which fits the 4n rule, indicating it is antiaromatic.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Frost Circle Diagram
A Frost circle diagram is a tool used to construct molecular orbital diagrams for cyclic conjugated systems. It involves inscribing a polygon representing the molecule inside a circle, with vertices touching the circle. The energy levels of the molecular orbitals are determined by the positions of these vertices, helping to predict the stability and aromaticity of the molecule.
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Inscribed Polygon Method
Aromaticity
Aromaticity is a property of cyclic, planar molecules with a ring of resonance bonds that leads to enhanced stability. According to Hückel's rule, a molecule is aromatic if it has (4n + 2) π electrons, where n is a non-negative integer. Aromatic compounds are typically more stable than their non-aromatic counterparts due to delocalized electrons.
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Antiaromaticity
Antiaromaticity refers to the instability in cyclic, planar molecules with a conjugated π electron system that follows the (4n) π electron rule. Unlike aromatic compounds, antiaromatic compounds are less stable due to the lack of electron delocalization, leading to increased reactivity. Understanding antiaromaticity is crucial for predicting the behavior of certain organic molecules.
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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?
699
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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?
(c)
426
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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)
788
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Textbook Question
(i) Classify the following molecules as aromatic, nonaromatic, or antiaromatic.
(ii) For aromatic molecules, solve for n in Hückel’s rule. For all other molecules, explain which rule of aromaticity is being broken.
(g)
451
views