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:Excited States

Organic Chemistry

16. Conjugated Systems

Orbital Diagram:Excited States

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3:59 minutes

Problem 15d,e

Textbook Question

Answer the following questions for the MOs of 1,3-butadiene:
d. Which MO is the HOMO and which is the LUMO in the excited state?
e. What is the relationship between the HOMO and the LUMO and symmetric and antisymmetric orbitals?

Verified step by step guidance

Step 1: Understand the molecular orbital (MO) theory for 1,3-butadiene. 1,3-butadiene has four π-electrons, which occupy molecular orbitals formed by the combination of the four p-orbitals on the carbon atoms. These MOs are labeled as π1, π2, π3*, and π4*, where π1 and π2 are bonding orbitals, and π3* and π4* are antibonding orbitals.

Step 2: Identify the HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) in the ground state. In the ground state, the four π-electrons fill the two lowest energy bonding orbitals, π1 and π2. Thus, π2 is the HOMO, and π3* is the LUMO in the ground state.

Step 3: Determine the HOMO and LUMO in the excited state. In the excited state, one electron from the HOMO (π2) is promoted to the LUMO (π3*). As a result, the new HOMO becomes π3*, and the new LUMO becomes π4*.

Step 4: Explain the relationship between symmetry and the MOs. Molecular orbitals can be classified as symmetric or antisymmetric based on their behavior under reflection through the molecular plane or inversion through the center of symmetry. For 1,3-butadiene, π1 and π3* are symmetric orbitals, while π2 and π4* are antisymmetric orbitals.

Step 5: Relate the HOMO and LUMO to symmetry. In the excited state, the HOMO (π3*) is symmetric, and the LUMO (π4*) is antisymmetric. This symmetry relationship is important for understanding electronic transitions and reactivity in conjugated systems.

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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 when atoms bond together. In the case of 1,3-butadiene, the MOs can be classified based on their energy levels, with the highest occupied molecular orbital (HOMO) being the highest energy orbital that contains electrons, and the lowest unoccupied molecular orbital (LUMO) being the lowest energy orbital that is empty. Understanding these orbitals is crucial for analyzing electronic transitions and reactivity.

HOMO and LUMO

The HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) are key concepts in molecular orbital theory that describe the electronic structure of a molecule. The HOMO is the orbital that contains the highest energy electrons, while the LUMO is the first available orbital for electron excitation. The energy gap between these two orbitals is significant for predicting the molecule's reactivity and absorption of light, particularly in excited states.

Symmetric and Antisymmetric Orbitals

Symmetric and antisymmetric orbitals refer to the behavior of molecular orbitals under the exchange of two identical particles, such as electrons. Symmetric orbitals remain unchanged when the particles are swapped, while antisymmetric orbitals change sign. This distinction is important in determining the allowed configurations of electrons in MOs, influencing the stability and reactivity of the molecule, particularly in the context of excited states and electronic transitions.

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