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

Cumulative Electrocyclic Problems

Organic Chemistry

16. Conjugated Systems

Cumulative Electrocyclic Problems

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Problem 37a

Textbook Question

For the following electrocyclic reactions, did the substituents move in a conrotatory or disrotatory direction? Would you use heat or light to cause movement in this direction?
(a)

Verified step by step guidance

Understand the concept of electrocyclic reactions: These are a type of pericyclic reaction where a pi bond is converted into a sigma bond or vice versa, often involving the cyclic movement of electrons.

Identify the type of electrocyclic reaction: Determine whether the reaction is a ring closure or ring opening, as this will influence the direction of substituent movement.

Determine the number of pi electrons involved: The number of pi electrons in the system will dictate whether the reaction proceeds via a conrotatory or disrotatory pathway.

Apply the Woodward-Hoffmann rules: These rules help predict the stereochemistry of electrocyclic reactions. For reactions involving 4n pi electrons, conrotatory motion is favored under thermal conditions, while disrotatory motion is favored under photochemical conditions. For reactions involving 4n+2 pi electrons, the opposite is true.

Decide on the use of heat or light: Based on the number of pi electrons and the desired stereochemical outcome (conrotatory or disrotatory), choose whether to apply heat or light to initiate the reaction.

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Key Concepts

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

Electrocyclic Reactions

Electrocyclic reactions are a type of pericyclic reaction where a pi-bonded system undergoes a ring closure or opening, resulting in a change in the number of pi bonds. These reactions are stereospecific and can proceed via conrotatory or disrotatory pathways, depending on the number of pi electrons and whether the reaction is thermally or photochemically induced.

Conrotatory and Disrotatory Motion

In electrocyclic reactions, conrotatory motion involves the simultaneous rotation of terminal substituents in the same direction, while disrotatory motion involves rotation in opposite directions. The type of motion is determined by the number of pi electrons and the conditions (heat or light) under which the reaction occurs, following the Woodward-Hoffmann rules.

Woodward-Hoffmann Rules

The Woodward-Hoffmann rules are a set of principles used to predict the stereochemistry of pericyclic reactions. For electrocyclic reactions, these rules state that reactions with 4n pi electrons proceed conrotatorily under thermal conditions and disrotatorily under photochemical conditions, while those with 4n+2 pi electrons proceed disrotatorily with heat and conrotatorily with light.

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