Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 19m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 18m
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 Acids3h 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

HOMO LUMO

Organic Chemistry

16. Conjugated Systems

HOMO LUMO

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8:04 minutes

Problem 21Mullins - 1st Edition

Textbook Question

Identify the HOMO and LUMO of the allylic cation and the allylic anion shown in Figure 21.22.

Verified step by step guidance

Identify the molecular orbitals involved in the allylic system. The allylic system consists of three p orbitals that can overlap to form molecular orbitals.

Determine the number of π electrons in the allylic cation and the allylic anion. The allylic cation has 2 π electrons, while the allylic anion has 4 π electrons.

For the allylic cation, fill the molecular orbitals with the 2 π electrons starting from the lowest energy orbital. The highest occupied molecular orbital (HOMO) will be the one containing the last electron.

For the allylic anion, fill the molecular orbitals with the 4 π electrons starting from the lowest energy orbital. The lowest unoccupied molecular orbital (LUMO) will be the first orbital that does not contain any electrons.

Visualize the molecular orbital diagram for both the allylic cation and anion to clearly identify which orbitals are the HOMO and LUMO based on the electron filling order.

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Key Concepts

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

HOMO and LUMO

HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) are key concepts in molecular orbital theory. The HOMO is the highest energy orbital that contains electrons, while the LUMO is the lowest energy orbital that is empty. The energy gap between these two orbitals is crucial for understanding the reactivity of molecules, as it influences how they interact with other species.

Allylic Cation and Anion

An allylic cation is a positively charged species where the positive charge is located on a carbon atom adjacent to a double bond, while an allylic anion has a negative charge on a similar carbon atom. These species are important in organic chemistry due to their stability and reactivity, which can be analyzed through their molecular orbitals. The resonance stabilization in these structures significantly affects their HOMO and LUMO energies.

Resonance

Resonance is a concept used to describe the delocalization of electrons in molecules that can be represented by two or more valid Lewis structures. In the case of allylic cations and anions, resonance allows for the distribution of charge over multiple atoms, which stabilizes the species. Understanding resonance is essential for predicting the behavior of these ions, including the characteristics of their HOMO and LUMO.