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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

HOMO LUMO

16. Conjugated Systems

HOMO LUMO: Videos & Practice Problems

Video Lessons Practice Worksheet

Topic summary

Frontier Molecular Orbital Theory (FMO) is crucial in organic chemistry, focusing on the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO). The HOMO is the highest energy orbital containing electrons, while the LUMO is the lowest energy orbital without electrons. For example, in ethene, the HOMO is the filled pi 1 orbital, and the LUMO is the unfilled pi 2* orbital. Understanding these concepts aids in predicting reaction mechanisms and interactions, such as electrophilic additions and regioselectivity in reactions.

Frontier orbital interations are the driving force behind many Organic Chemistry recations. Let's find out why.

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HOMO vs. LUMO

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HOMO vs. LUMO Video Summary

Frontier Molecular Orbital Theory (FMOT) is a crucial concept in organic chemistry that helps explain the reactivity of molecules. Understanding FMOT is foundational for grasping various chemical reactions. The key components of this theory are the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO).

The HOMO is defined as the molecular orbital with the highest energy that still contains electrons. Conversely, the LUMO is the molecular orbital with the lowest energy that does not contain any electrons. To illustrate this, consider the example of ethene (C₂H₄), a simple molecule that can help clarify these concepts.

In ethene, two atomic orbitals combine to form two molecular orbitals: a bonding orbital and an antibonding orbital. According to the principles of electron configuration, the two electrons in ethene will occupy the lowest energy bonding orbital, referred to as π₁. This means that the HOMO for ethene is π₁, which contains the two electrons. The LUMO, on the other hand, is the antibonding orbital, π₂^*, which is unoccupied and has no electrons.

In summary, for ethene, the HOMO is π₁ with 2 electrons, while the LUMO is π₂^* with 0 electrons. As molecules become larger and more complex, identifying the HOMO and LUMO involves determining the boundary between filled and unfilled molecular orbitals. This understanding is essential for predicting how molecules will interact in chemical reactions.

HOMO = Highest Occupied Molecular Orbital

LUMO = Lowest Unoccupied Molecular Orbital

Problem

Consider the MO's of allyl anion. Which of the following are HOMO and LUMO?

HOMO = B, LUMO = C

HOMO = B, LUMO = A

HOMO = C, LUMO = A

HOMO = A, LUMO = C

HOMO = C, LUMO = B

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Here’s what students ask on this topic:

What is the significance of HOMO and LUMO in organic chemistry?

HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) are crucial in organic chemistry because they help predict how molecules will interact in chemical reactions. The HOMO represents the highest energy orbital that contains electrons, while the LUMO is the lowest energy orbital that does not contain electrons. The energy gap between HOMO and LUMO, known as the HOMO-LUMO gap, determines the molecule's reactivity. For instance, in electrophilic addition reactions, the HOMO of one molecule interacts with the LUMO of another, facilitating the reaction. Understanding these orbitals aids in predicting reaction mechanisms and regioselectivity.

How do you determine the HOMO and LUMO of a molecule?

To determine the HOMO and LUMO of a molecule, you need to look at its molecular orbitals. The HOMO is the highest energy orbital that contains electrons, while the LUMO is the lowest energy orbital that does not contain electrons. For example, in ethene (C₂H₄), the HOMO is the filled π₁ orbital, and the LUMO is the unfilled π₂* orbital. As molecules get larger, the number of molecular orbitals increases, and the HOMO and LUMO are found at the boundary where the filled orbitals end and the unfilled orbitals begin.

What is the HOMO-LUMO gap, and why is it important?

The HOMO-LUMO gap is the energy difference between the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO). This gap is crucial because it determines a molecule's chemical reactivity and stability. A smaller HOMO-LUMO gap means the molecule is more reactive, as it requires less energy for an electron to transition from the HOMO to the LUMO. This concept is essential in understanding reaction mechanisms, such as electrophilic additions, and in designing molecules for specific functions, like organic semiconductors.

How does the concept of HOMO and LUMO apply to electrophilic addition reactions?

In electrophilic addition reactions, the HOMO and LUMO play a critical role in determining how the reaction proceeds. The HOMO of the nucleophile (electron-rich species) interacts with the LUMO of the electrophile (electron-deficient species). For example, in the addition of HBr to ethene, the π₁ orbital (HOMO) of ethene interacts with the σ* orbital (LUMO) of HBr. This interaction facilitates the breaking of the H-Br bond and the formation of new bonds, leading to the addition product. Understanding HOMO and LUMO helps predict the regioselectivity and outcome of such reactions.

Can you explain the role of HOMO and LUMO in predicting regioselectivity?

HOMO and LUMO are essential in predicting regioselectivity, which is the preference for a chemical bond to form at one direction over another in a molecule. In reactions, the HOMO of one molecule interacts with the LUMO of another. The regions of highest electron density in the HOMO will interact with the regions of lowest electron density in the LUMO. For example, in the Diels-Alder reaction, the HOMO of the diene interacts with the LUMO of the dienophile, determining the regioselectivity of the product. Understanding these interactions helps chemists predict and control the outcomes of reactions.