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

Pericyclic Reaction

Organic Chemistry

16. Conjugated Systems

Pericyclic Reaction

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Problem 1

Textbook Question

Examine the following pericyclic reactions. For each reaction, tell whether it is an electrocyclic reaction, a cycloaddition reaction, or a sigmatropic rearrangement.
a.
b.
c.
d.

Verified step by step guidance

Step 1: Understand the three types of pericyclic reactions. An electrocyclic reaction involves the opening or closing of a conjugated π-system to form a new σ-bond or break an existing one. A cycloaddition reaction involves the formation of a cyclic product by the combination of two π-systems. A sigmatropic rearrangement involves the migration of a σ-bond across a π-system, with the overall connectivity of the molecule remaining unchanged.

Step 2: Analyze reaction (a). Look for changes in the π-system and determine if a new σ-bond is formed (electrocyclic), if two π-systems combine to form a ring (cycloaddition), or if a σ-bond migrates across a π-system (sigmatropic rearrangement).

Step 3: Analyze reaction (b). Use the same criteria as in Step 2 to classify the reaction. Pay attention to the movement of electrons and the formation or breaking of bonds.

Step 4: Analyze reaction (c). Again, determine whether the reaction involves the opening/closing of a π-system (electrocyclic), the combination of two π-systems (cycloaddition), or the migration of a σ-bond (sigmatropic rearrangement).

Step 5: Analyze reaction (d). Follow the same process as in the previous steps to classify the reaction based on the changes in bonding and electron movement.

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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 a cyclic transition state. These reactions typically involve the rearrangement of electrons in a way that conserves orbital symmetry, and they can be classified into three main types: electrocyclic reactions, cycloadditions, and sigmatropic rearrangements.

Electrocyclic Reactions

Electrocyclic reactions involve the conversion of a conjugated system into a cyclic structure through the breaking and forming of sigma bonds. These reactions are characterized by the movement of electrons in a way that can be influenced by heat or light, and they follow specific rules based on the number of π electrons involved, as described by the Woodward-Hoffmann rules.

Cycloaddition Reactions

Cycloaddition reactions are a type of pericyclic reaction where two or more unsaturated molecules or fragments combine to form a cyclic product. These reactions can be classified as [2+2] or [4+2] cycloadditions, depending on the number of π bonds involved. The stereochemistry and regioselectivity of these reactions are crucial for determining the structure of the final product.

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