Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

16. Conjugated Systems

Orbital Diagram:5-atoms- Allylic Ions

Organic Chemistry

16. Conjugated Systems

Orbital Diagram:5-atoms- Allylic Ions

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5:21 minutes

Problem 37h

Textbook Question

The pentadienyl radical, H₂C=CH–CH=CH–CH₂•, has its unpaired electron delocalized over three carbon atoms.
h. Add an electron to the pentadienyl radical to give the pentadienyl anion. Which carbon atoms share the negative charge? Does this picture agree with the resonance picture?

Verified step by step guidance

Step 1: Understand the structure of the pentadienyl radical. The pentadienyl radical, H₂C=CH-CH=CH-CH₂·, is a conjugated system with alternating double and single bonds. The unpaired electron is delocalized over the three central carbon atoms (C2, C3, and C4) due to resonance.

Step 2: Add an electron to the pentadienyl radical. Adding an electron to the radical will pair with the unpaired electron, resulting in a pentadienyl anion. This anion now has a negative charge that is delocalized over the conjugated system.

Step 3: Draw the resonance structures of the pentadienyl anion. The negative charge is delocalized over the three central carbon atoms (C2, C3, and C4) through resonance. Write out the resonance structures to visualize how the negative charge shifts between these carbons.

Step 4: Analyze the resonance picture. The resonance structures show that the negative charge is shared among C2, C3, and C4. This delocalization stabilizes the anion and agrees with the resonance picture of the pentadienyl radical.

Step 5: Conclude the analysis. The negative charge in the pentadienyl anion is shared over the three central carbon atoms (C2, C3, and C4), and this picture is consistent with the resonance structures. This delocalization is a key feature of conjugated systems and contributes to the stability of the anion.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Radicals and Anions

Radicals are species with unpaired electrons, making them highly reactive. In contrast, anions are negatively charged species that have gained an electron. The pentadienyl radical has an unpaired electron that can be stabilized by delocalization across multiple carbon atoms. When an electron is added to form the pentadienyl anion, the negative charge is distributed among the carbon atoms involved in the double bonds.

Delocalization of Electrons

Delocalization refers to the spreading of electrons across multiple atoms rather than being localized between two. In the case of the pentadienyl radical and anion, the unpaired electron and the added electron can be delocalized over the carbon atoms involved in the conjugated system. This delocalization stabilizes the radical and anion, allowing for resonance structures that depict the distribution of the negative charge.

Resonance Structures

Resonance structures are different ways of drawing a molecule that illustrate the delocalization of electrons. For the pentadienyl anion, resonance structures show how the negative charge can be shared among different carbon atoms. This concept helps in understanding the stability of the anion, as the actual structure is a hybrid of these resonance forms, reflecting the distribution of the negative charge across the molecule.

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Textbook Question

The pentadienyl radical, H₂C=CH–CH=CH–CH₂•, has its unpaired electron delocalized over three carbon atoms.

a. Use resonance forms to show which three carbon atoms bear the unpaired electron.

Textbook Question

The pentadienyl radical, H₂C=CH–CH=CH–CH₂•, has its unpaired electron delocalized over three carbon atoms.

b. How many MOs are there in the molecular orbital picture of the pentadienyl radical?

c. How many nodes are there in the lowest-energy MO of the pentadienyl system? How many in the highest-energy MO?

d. Draw the MOs of the pentadienyl system in order of increasing energy

Textbook Question

The pentadienyl radical, H₂C=CH–CH=CH–CH₂•, has its unpaired electron delocalized over three carbon atoms.

f. Show how your molecular orbital picture agrees with the resonance picture showing delocalization of the unpaired electron onto three carbon atoms.

Textbook Question

The pentadienyl radical, H₂C=CH–CH=CH–CH₂•, has its unpaired electron delocalized over three carbon atoms.

g. Remove the highest-energy electron from the pentadienyl radical to give the pentadienyl cation. Which carbon atoms share the positive charge? Does this picture agree with the resonance picture?

Textbook Question

Answer the following questions for the MOs of 1,3-butadiene:

a. Which are $π$ bonding MOs, and which are $π$ * antibonding MOs?

b. Which MOs are symmetric, and which are antisymmetric?

c. Which MO is the HOMO and which is the LUMO in the ground state?

Open Question

Predict the molecular orbitals and identify the HOMO and LUMO orbitals of the following cation.

Textbook Question

The pentadienyl radical, H₂C=CH–CH=CH–CH₂•, has its unpaired electron delocalized over three carbon atoms.

a. Use resonance forms to show which three carbon atoms bear the unpaired electron.

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The pentadienyl radical, H2C=CH–CH=CH–CH2•, has its unpaired electron delocalized over three carbon atoms.h. Add an electron to the pentadienyl radical to give the pentadienyl anion. Which carbon atoms share the negative charge? Does this picture agree with the resonance picture?

Key Concepts

Radicals and Anions

Delocalization of Electrons

Resonance Structures

Watch next

The pentadienyl radical, H₂C=CH–CH=CH–CH₂•, has its unpaired electron delocalized over three carbon atoms.
h. Add an electron to the pentadienyl radical to give the pentadienyl anion. Which carbon atoms share the negative charge? Does this picture agree with the resonance picture?