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

Photochemical Cycloaddition Reactions

Organic Chemistry

16. Conjugated Systems

Photochemical Cycloaddition Reactions

Previous problemNext problem

7:55 minutes

Problem 11

Textbook Question

Will a concerted reaction take place between 1,3-butadiene and 2-cyclohexenone in the presence of ultraviolet light?

Verified step by step guidance

Identify the type of reaction: The problem involves 1,3-butadiene and 2-cyclohexenone, which suggests a potential pericyclic reaction. Since ultraviolet (UV) light is mentioned, this indicates the possibility of a photochemical reaction, such as a [2+2] cycloaddition.

Understand the reaction conditions: In the presence of UV light, pericyclic reactions follow the photochemical selection rules. These rules are based on the Woodward-Hoffmann principles, which determine whether a reaction is allowed under thermal or photochemical conditions.

Analyze the molecular orbitals: For a [2+2] cycloaddition to occur, the reaction must involve the interaction of the HOMO (highest occupied molecular orbital) of one molecule with the LUMO (lowest unoccupied molecular orbital) of the other. Under photochemical conditions, the electronic excitation alters the orbital symmetry, making the reaction symmetry-allowed.

Determine the feasibility of the reaction: 1,3-butadiene has a conjugated π-system, and 2-cyclohexenone contains a double bond in a cyclic structure. Under UV light, the π-electrons in these molecules can be excited, allowing the reaction to proceed via a concerted mechanism. This makes the [2+2] cycloaddition between these two molecules feasible.

Conclude the reaction type: Based on the analysis, a concerted [2+2] cycloaddition reaction is likely to occur between 1,3-butadiene and 2-cyclohexenone in the presence of UV light, as it satisfies the photochemical selection rules.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

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

Concerted Reactions

Concerted reactions are chemical processes where bond breaking and bond forming occur simultaneously in a single step, without intermediates. This mechanism is crucial in understanding how certain reactions proceed, particularly in systems with multiple reactive sites. The stereochemistry and regioselectivity of the products are often determined by the concerted nature of the reaction.

Diels-Alder Reaction

The Diels-Alder reaction is a specific type of concerted reaction involving a diene and a dienophile, leading to the formation of a six-membered ring. In this context, 1,3-butadiene acts as the diene, while 2-cyclohexenone serves as the dienophile. This reaction is thermally allowed and can be influenced by light, making it relevant to the question of ultraviolet light's effect.

Ultraviolet Light in Organic Reactions

Ultraviolet (UV) light can provide the energy necessary to promote certain organic reactions, particularly those involving excited states or radical mechanisms. In the context of the question, UV light may facilitate the Diels-Alder reaction by promoting the diene or dienophile to a reactive state, potentially altering the reaction pathway or rate. Understanding the role of UV light is essential for predicting the feasibility of the reaction.

Watch next

Master MO Theory of Photochemical Cycloadditions with a bite sized video explanation from Johnny

Start learning