Textbook Question
Molecule A is significantly more water soluble than molecule B. Justify this observation.
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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 63
Mullins 1st EditionCh. 23 - Benzene I: Aromatic Stability and Substitution ReactionsProblem 63Chapter 22, Problem 63
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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Identify the structure in question: The cyclopentadienyl anion is a five-membered ring with a negative charge, which means it has 6 π electrons (4 from the double bonds and 2 from the negative charge).
Apply Hückel's rule for aromaticity: A molecule is aromatic if it is cyclic, planar, fully conjugated, and has 4n+2 π electrons, where n is a non-negative integer.
Determine the number of π electrons: The cyclopentadienyl anion has 6 π electrons, which fits the 4n+2 rule (n=1, since 4(1)+2=6).
Analyze the Frost circle diagram: The Frost circle for a five-membered ring should have one molecular orbital at the bottom, two degenerate orbitals in the middle, and two degenerate orbitals at the top. The diagram shows that all 6 π electrons fill the bonding orbitals, which is consistent with aromaticity.
Conclude based on the analysis: Since the cyclopentadienyl anion satisfies all the criteria for aromaticity, including the 4n+2 rule, it is aromatic, not antiaromatic. Therefore, the student's conclusion is incorrect.
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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 the context of cyclopentadienyl anion, understanding how the p orbitals overlap to create bonding and antibonding MOs is crucial. The arrangement and energy levels of these orbitals determine the stability and reactivity of the molecule.
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Review of Molecular Orbitals
Aromaticity and Antiaromaticity
Aromatic compounds are cyclic, planar molecules with a continuous overlap of p orbitals, allowing for delocalized π electrons that follow Hückel's rule (4n + 2 π electrons). In contrast, antiaromatic compounds have 4n π electrons, leading to destabilization. Recognizing these criteria is essential for evaluating the cyclopentadienyl anion's classification.
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Frost Circle
The Frost circle is a graphical method used to determine the molecular orbitals of cyclic compounds. By inscribing the polygon corresponding to the number of carbon atoms in a circle and marking the points where the vertices touch the circle, one can visualize the energy levels of the MOs. This tool is particularly useful for assessing the aromatic or antiaromatic nature of cyclic systems like the cyclopentadienyl anion.
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Related Practice
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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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?
(c)
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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)
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