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

Conjugation Chemistry

Organic Chemistry

16. Conjugated Systems

Conjugation Chemistry

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2:01 minutes

Problem 86a

Textbook Question

Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:
a. How many MOs does the compound have?

Verified step by step guidance

Count the number of conjugated π-electrons in the molecule. In 1,3,5,7-octatetraene, there are four double bonds, each contributing two π-electrons, for a total of 8 π-electrons.

Determine the number of atomic p orbitals involved in the conjugated π-system. Each carbon atom in the conjugated system contributes one p orbital. Since there are 8 carbons in the conjugated system, there are 8 p orbitals.

Recall that the number of molecular orbitals (MOs) formed in a conjugated π-system is equal to the number of atomic p orbitals involved. Therefore, 8 MOs will be formed.

Understand that these 8 MOs will include bonding, non-bonding, and anti-bonding orbitals, arranged in increasing energy levels based on the overlap of the p orbitals.

Conclude that the compound 1,3,5,7-octatetraene has 8 molecular orbitals (MOs) in its conjugated π-system.

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Key Concepts

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

Molecular Orbitals (MOs)

Molecular orbitals are formed by the linear combination of atomic orbitals (LCAO) when atoms bond together. In a molecule, these orbitals can be occupied by electrons and are classified as bonding, antibonding, or non-bonding. The number of MOs corresponds to the number of atomic orbitals that combine, which is crucial for understanding the electronic structure of the molecule.

Conjugation

Conjugation refers to the overlap of p-orbitals across adjacent double bonds, allowing for delocalization of electrons. In 1,3,5,7-octatetraene, the alternating double bonds create a system of conjugated MOs, which lowers the energy of the system and increases stability. This concept is essential for determining the number and type of MOs in conjugated systems.

Counting Molecular Orbitals

The total number of molecular orbitals in a molecule is equal to the number of atomic orbitals that combine to form them. For 1,3,5,7-octatetraene, which has eight carbon atoms, each contributing one p-orbital, the total number of MOs is equal to the number of contributing atomic orbitals. This principle is fundamental for calculating the MOs in any given molecule.

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Related Practice

Textbook Question

Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:

g. How many nodes does the highest-energy MO of 1,3,5,7-octatetraene have between the nuclei?

Textbook Question

Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:

e. Which MO is the HOMO and which is the LUMO in the excited state?

Textbook Question

Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:

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

Textbook Question

Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:

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

Textbook Question

For the following terpenes, identify the isoprene units. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene

(b)

Textbook Question

For the following terpenes, identify the isoprene units. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene

(c)

Textbook Question

North American termite soldiers, when encountering enemy insects, contract their mandibular muscles, expelling a mixture of chemicals that essentially trap their enemies in a glue-like substance. This weapon, built into the face of the termite, is called the fontanellar gun. It releases a mixture of pinene (62%), myrcene (27%), and limonene (11%). pinene myrcene limonene 62% 27% 11%

(a) Identify the isoprene units in pinene, myrcene, and limonene.

Textbook Question

Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene:

b. Which are the bonding MOs, and which are the antibonding MOs?

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