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

Diels-Alder Reaction

Organic Chemistry

16. Conjugated Systems

Diels-Alder Reaction

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Problem 12

Textbook Question

Which of the following concerted reactions would have a more stable transition state? Why?

Verified step by step guidance

Identify the type of reaction depicted in each image. Both reactions are examples of pericyclic reactions, specifically cycloaddition reactions. The first image shows a Diels-Alder reaction, while the second image shows a [2+2] cycloaddition.

Consider the molecular orbitals involved in each reaction. The Diels-Alder reaction involves a diene and a dienophile, which typically have favorable orbital interactions due to the overlap of the highest occupied molecular orbital (HOMO) of the diene and the lowest unoccupied molecular orbital (LUMO) of the dienophile.

Analyze the symmetry and energy of the transition states. The Diels-Alder reaction generally has a more stable transition state due to the favorable overlap of orbitals and the formation of a six-membered ring, which is energetically favorable.

Evaluate the second reaction, the [2+2] cycloaddition. This reaction often has less favorable orbital interactions because it involves the overlap of two π systems, which can lead to higher energy and less stable transition states.

Conclude that the Diels-Alder reaction is likely to have a more stable transition state due to the favorable orbital interactions and the formation of a six-membered ring, which is typically more stable than the four-membered ring formed in the [2+2] cycloaddition.

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Key Concepts

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

Concerted Reactions

Concerted reactions are chemical reactions where all bond-breaking and bond-forming processes occur simultaneously in a single step. This type of reaction does not involve any intermediates, and the transition state is the highest energy point along the reaction pathway. Understanding the concerted nature of a reaction is crucial for analyzing its mechanism and stability.

Transition State Stability

The stability of a transition state in a chemical reaction is influenced by factors such as steric hindrance, electronic effects, and the degree of bond formation and breaking. A more stable transition state generally corresponds to a lower activation energy, making the reaction more favorable. In concerted reactions, the transition state stability is critical in determining the reaction's feasibility and rate.

Pericyclic Reactions

Pericyclic reactions are a class of concerted reactions characterized by a cyclic redistribution of bonding electrons through a transition state. These reactions include cycloadditions, electrocyclic reactions, and sigmatropic rearrangements. The stability of the transition state in pericyclic reactions is often analyzed using orbital symmetry considerations, such as the Woodward-Hoffmann rules, which predict the feasibility of the reaction based on the conservation of orbital symmetry.

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