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

9. Alkenes and Alkynes

Hydrogenation of Alkynes

Organic Chemistry

9. Alkenes and Alkynes

Hydrogenation of Alkynes

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2:23 minutes

Problem 7a

Textbook Question

We have studied a number of pericyclic reactions previously. Draw the mechanism of the steps shown. The section number where this material was first studied is given for your review.
(a)

Verified step by step guidance

Step 1: Identify the type of pericyclic reaction involved. Pericyclic reactions include cycloadditions, electrocyclic reactions, sigmatropic rearrangements, and cheletropic reactions. Determine which category the reaction falls into based on the provided mechanism.

Step 2: Analyze the molecular orbitals involved in the reaction. For example, in a cycloaddition reaction, consider the interaction between the π orbitals of the reactants. Use the Woodward-Hoffmann rules to determine whether the reaction is thermally or photochemically allowed.

Step 3: Draw the transition state of the reaction. Pericyclic reactions proceed through a concerted mechanism, meaning all bond-making and bond-breaking events occur simultaneously. Represent the cyclic flow of electrons using curved arrows to show how bonds are formed and broken.

Step 4: Verify the stereochemistry of the product. Pericyclic reactions often exhibit stereospecificity. For example, in an electrocyclic reaction, the stereochemistry of the product depends on whether the reaction is thermal or photochemical.

Step 5: Review the section number provided in the problem to revisit the theoretical concepts and examples studied earlier. This will help reinforce your understanding of the mechanism and ensure accuracy in your drawing.

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Key Concepts

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

Pericyclic Reactions

Pericyclic reactions are a class of organic reactions that occur through a concerted mechanism, involving the cyclic rearrangement of electrons. These reactions typically involve the overlap of orbitals in a cyclic transition state, leading to the formation of new bonds without the need for intermediates. Common types include cycloadditions, electrocyclic reactions, and sigmatropic rearrangements, each governed by specific selection rules.

Mechanism of Reactions

The mechanism of a reaction describes the step-by-step process by which reactants are converted into products. It includes the identification of intermediates, transition states, and the movement of electrons, often illustrated using curved arrows. Understanding the mechanism is crucial for predicting the outcome of reactions and for designing synthetic pathways in organic chemistry.

Orbital Overlap and Hybridization

Orbital overlap refers to the interaction between atomic orbitals that leads to the formation of chemical bonds. In pericyclic reactions, the overlap of p-orbitals is essential for the concerted nature of the reaction. Hybridization, the mixing of atomic orbitals to form new hybrid orbitals, also plays a role in determining the geometry and reactivity of the molecules involved, influencing the reaction pathway.

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