교과서 질문
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
16장, 문제 10
(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?
검증된 단계별 안내1
Step 1: Begin by identifying the cyclopropenyl system. Cyclopropenyl is a three-membered ring with conjugated π-electrons. The three p orbitals from the carbon atoms interact to form molecular orbitals.
Step 2: Draw the molecular orbitals (MOs) for the cyclopropenyl system. Since there are three p orbitals, there will be three MOs: one bonding MO (all p orbitals in-phase), one nonbonding MO (degenerate pair with one node), and one antibonding MO (all p orbitals out-of-phase). Use symmetry principles to sketch these orbitals.
Step 3: Construct an energy diagram using the polygon rule. The cyclopropenyl ring is triangular, so the energy levels of the MOs will follow the shape of the triangle. Place the bonding MO at the lowest energy, the degenerate nonbonding pair in the middle, and the antibonding MO at the highest energy. Label each MO as bonding, nonbonding, or antibonding.
Step 4: Add electrons to the energy diagram for the cyclopropenyl cation and anion. The cation has 2 π-electrons, which will fill the bonding MO, making it aromatic (Hückel's rule: 4n+2 π-electrons). The anion has 4 π-electrons, which will fill the bonding and nonbonding MOs, making it antiaromatic (4n π-electrons).
Step 5: Summarize the aromaticity. The cyclopropenyl cation is aromatic due to its 2 π-electrons satisfying Hückel's rule, while the cyclopropenyl anion is antiaromatic due to its 4 π-electrons violating Hückel's rule.
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주요 개념
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Molecular Orbitals (MOs)
Molecular orbitals are formed by the combination of atomic orbitals when atoms bond together. In the case of cyclopropenyl, three p orbitals combine to create three MOs: one bonding and a degenerate pair of antibonding orbitals. Understanding how these orbitals are filled with electrons is crucial for predicting the molecule's stability and reactivity.
추천 영상:
08:41
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 instability. Identifying whether cyclopropenyl cation or anion is aromatic or antiaromatic is essential for understanding their chemical behavior.
추천 영상:
02:58Determine the aromaticity
Energy Diagrams
Energy diagrams visually represent the relative energy levels of molecular orbitals. They help in understanding the stability of a molecule based on the filling of these orbitals. In the case of cyclopropenyl, the energy diagram will show the bonding, nonbonding, and antibonding MOs, which are crucial for determining the electronic configuration of the cation and anion.
추천 영상:
08:30Introduction to free energy diagrams.
관련 실천
교과서 질문
Explain why each compound or ion should be aromatic, antiaromatic, or nonaromatic.
(d)
(e)
(f) the [20]annulene dication
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교과서 질문
One of the following compounds is much more stable than the other two. Classify each as aromatic, antiaromatic, or nonaromatic.
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교과서 질문
a. Use the polygon rule to draw an energy diagram (as in Figures 16-5 and 16-7) for the MOs of a planar cyclooctatetraenyl system.
b. Fill in the eight pi electrons for cyclooctatetraene. Is this electronic configuration aromatic or antiaromatic? Could the cyclooctatetraene system be aromatic if it gained or lost electrons?
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교과서 질문
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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교과서 질문
Explain why each compound or ion should be aromatic, antiaromatic, or nonaromatic.
(a)
(b)
(c)
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