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

Thermal Electrocyclic Reactions

Organic Chemistry

16. Conjugated Systems

Thermal Electrocyclic Reactions

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Problem 40

Textbook Question

cis-3,4-Dimethylcyclobutene undergoes thermal ring opening to form the two products shown. One of the products is formed in 99% yield, the other in 1% yield. Which is which?

Verified step by step guidance

Step 1: Recognize that the thermal ring opening of cis-3,4-dimethylcyclobutene is a pericyclic reaction, specifically a conrotatory ring-opening process governed by the Woodward-Hoffmann rules for electrocyclic reactions.

Step 2: Analyze the stereochemistry of the starting material. The cis configuration of the methyl groups on the cyclobutene ring will influence the geometry of the products formed during the ring-opening process.

Step 3: Predict the products based on the conrotatory mechanism. The conrotatory motion will lead to two possible products: one with conjugated double bonds (more stable due to resonance stabilization) and another with isolated double bonds (less stable).

Step 4: Compare the stability of the two products. The product with conjugated double bonds is significantly more stable due to delocalization of π-electrons, which lowers the overall energy of the molecule. The product with isolated double bonds lacks this stabilization.

Step 5: Assign the major and minor products based on their stability. The conjugated product is formed in 99% yield due to its greater thermodynamic stability, while the isolated double bond product is formed in only 1% yield.

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Key Concepts

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

Thermal Ring Opening

Thermal ring opening refers to the process where a cyclic compound, such as a cyclobutene, undergoes a reaction upon heating that breaks the ring structure, resulting in the formation of linear or branched products. This reaction is often favored in certain cyclic compounds due to the strain in the ring, which can be relieved by forming more stable open-chain structures.

Regioselectivity

Regioselectivity is the preference of a chemical reaction to yield one structural isomer over others when multiple products are possible. In the case of the thermal ring opening of cis-3,4-Dimethylcyclobutene, the formation of one product in 99% yield suggests that the reaction is highly regioselective, favoring the formation of a more stable or lower-energy product due to factors such as sterics or electronic effects.

Stability of Alkenes

The stability of alkenes is influenced by their degree of substitution; more substituted alkenes are generally more stable due to hyperconjugation and the inductive effect. In the context of the products formed from the ring opening of cis-3,4-Dimethylcyclobutene, the more substituted alkene is likely the one formed in higher yield, as it is thermodynamically favored compared to the less substituted counterpart.

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