Domanda del libro di testo
Drawpictorialrepresentations (as in Figures16-4 and 16-6) for the three bonding MOs and the two nonbonding MOs of cyclooctatetraene. The antibonding MOs are difficult to draw, except for the all-antibonding MO.
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Ch. 16 - Aromatic Compounds
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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TOC.tableOfContents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Capitolo 16, Problema 12a,b,c
Explain why each compound or ion should be aromatic, antiaromatic, or nonaromatic.
(a) 
(b) 
(c) 
Guida verificata passo dopo passo1
Step 1: Recall the criteria for aromaticity. A compound is aromatic if it satisfies the following conditions: (a) It is cyclic, (b) It is planar, (c) It has a conjugated π-electron system, and (d) It follows Hückel's rule, which states that the molecule must have (4n + 2) π-electrons, where n is a non-negative integer.
Step 2: Analyze compound (a), the cyclononatetraene cation. This molecule is cyclic and conjugated, but it has 8 π-electrons (from 4 double bonds). Since 8 does not satisfy Hückel's rule (4n + 2), the molecule is antiaromatic if it is planar. If it is non-planar, it would be nonaromatic.
Step 3: Analyze compound (b), the cyclononatetraene anion. This molecule is cyclic and conjugated, and it has 10 π-electrons (from 4 double bonds and 2 electrons from the negative charge). Since 10 satisfies Hückel's rule (4n + 2, where n = 2), the molecule is aromatic if it is planar.
Step 4: Analyze compound (c), the [16]annulene dianion. This molecule is cyclic and conjugated, and it has 18 π-electrons (from 8 double bonds and 2 electrons from the negative charges). Since 18 satisfies Hückel's rule (4n + 2, where n = 4), the molecule is aromatic if it is planar. However, steric hindrance due to the hydrogen atoms inside the ring may affect planarity.
Step 5: Summarize the findings. Compound (a) is antiaromatic if planar, compound (b) is aromatic if planar, and compound (c) is aromatic if planar but may face steric hindrance affecting its aromaticity.
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Aromaticity
Aromatic compounds are cyclic, planar molecules with a ring of resonance that follow Hückel's rule, which states they must have 4n + 2 π electrons (where n is a non-negative integer). This delocalization of electrons contributes to their stability and unique chemical properties. Common examples include benzene and its derivatives.
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08:19
Intro to Aromaticity
Antiaromaticity
Antiaromatic compounds are also cyclic and planar but contain 4n π electrons, leading to destabilization due to the presence of electron-electron repulsion. This instability often results in higher reactivity compared to nonaromatic compounds. Cyclobutadiene is a classic example of an antiaromatic compound.
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02:58Determine the aromaticity
Nonaromaticity
Nonaromatic compounds do not meet the criteria for aromaticity or antiaromaticity. They may be acyclic, lack planarity, or have an insufficient number of π electrons. These compounds do not exhibit the special stability associated with aromatic systems, and their reactivity is typically similar to that of aliphatic compounds.
Pratica correlata
Domanda del libro di testo
Explain why each compound or ion should be aromatic, antiaromatic, or nonaromatic.
(d)
(e)
(f) the [20]annulene dication
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Domanda del libro di testo
When 3-chlorocyclopropene is treated with AgBF4, AgCl precipitates. The organic product can be obtained as a crystalline material, soluble in polar solvents such as nitromethane but insoluble in hexane. When the crystalline material is dissolved in nitromethane containing KCl, the original 3-chlorocyclopropene is regenerated. Determine the structure of the crystalline material, and write equations for its formation and its reaction with chloride ion.
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The following hydrocarbon has an unusually large dipole moment. Explain how a large dipole moment might arise.
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Domanda del libro di testo
(a) Draw the molecular orbitals for the cyclopropenyl case.
(Because there are three p orbitals, there must be three MOs: one all-bonding MO and one degenerate pair of MOs.)
(b) Draw an energy diagram for the cyclopropenyl MOs. (The polygon rule is helpful.) Label each MO as bonding, nonbonding, or antibonding, and add the nonbonding line. Notice that it goes through the approximate average of the MOs.
(c) Add electrons to your energy diagram to show the configuration of the cyclopropenyl cation and the cyclopropenyl anion. Which is aromatic and which is antiaromatic?
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Domanda del libro di testo
Repeat Problem 16-10 for the cyclopentadienyl ions. Draw one all-bonding MO, then a pair of degenerate MOs, and then a final pair of degenerate MOs. Draw the energy diagram, fill in the electrons, and confirm the electronic configurations of the cyclopentadienyl cation and anion.
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