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

Sigmatropic Rearrangement

Organic Chemistry

16. Conjugated Systems

Sigmatropic Rearrangement

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14:02 minutes

Problem 36

Textbook Question

Propose a mechanism for the following reaction:

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Step 1: Analyze the reactants and products. The reactants include a nitro-substituted pyridine and an ester with two carbonyl groups. The products are a substituted pyridine derivative (A) and a carboxylic acid (B). This suggests a nucleophilic acyl substitution mechanism.

Step 2: Identify the reactive sites. The nitro group on the pyridine ring is electron-withdrawing, making the pyridine ring more electrophilic. The ester contains two carbonyl groups, which are susceptible to nucleophilic attack.

Step 3: Initiate the reaction mechanism. Heat (Δ) facilitates the reaction. The pyridine nitrogen acts as a nucleophile and attacks the carbonyl carbon of the ester, forming a tetrahedral intermediate.

Step 4: Collapse of the tetrahedral intermediate. The intermediate collapses, expelling the ethoxide group (CH₂CH₃O⁻) and forming a new bond between the pyridine nitrogen and the carbonyl carbon. This results in the formation of product A.

Step 5: Formation of product B. The expelled ethoxide group reacts with a proton to form ethanol (CH₃CH₂OH), which subsequently oxidizes to form the carboxylic acid product B.

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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 class of pericyclic reactions where a conjugated system undergoes a concerted transformation to form a cyclic compound. These reactions are characterized by the rotation of a sigma bond and the formation or breaking of pi bonds, often influenced by thermal or photochemical conditions. Understanding the stereochemistry and the rules governing these reactions, such as the Woodward-Hoffmann rules, is crucial for predicting the products.

Mechanism of Reaction

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 sequence of bond-breaking and bond-forming events. Proposing a mechanism requires knowledge of reaction conditions, the stability of intermediates, and the energy changes involved, which are essential for understanding how the reaction proceeds.

Thermal Conditions in Organic Reactions

Thermal conditions refer to the influence of heat on the rate and outcome of chemical reactions. In organic chemistry, heating can provide the necessary energy to overcome activation barriers, facilitating reactions such as electrocyclic transformations. The temperature can also affect the selectivity and stereochemistry of the products, making it important to consider when proposing mechanisms for reactions that involve heat.

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Related Practice

Textbook Question

b. Using arrows, show the electron rearrangement that takes place in each reaction.

Textbook Question

A student found that heating any one of the isomers shown here resulted in scrambling of the deuterium to all three positions on the five-membered ring. Propose a mechanism to account for this observation.

Textbook Question

Draw the product of each of the following sigmatropic rearrangements:

Textbook Question

Draw the product of each of the following sigmatropic rearrangements:

Textbook Question

If the compounds shown here are heated, one will form one product from a [1,3] sigmatropic rearrangement and the other will form two products from two different [1,3] sigmatropic rearrangements. Draw the products of the reactions.

Textbook Question

What is the product of the following [1,3] sigmatropic rearrangement, A or B?

Textbook Question

a. Will thermal 1,3-migrations of carbon occur with retention or inversion of configuration?

Multiple Choice

Provide the correct names and mechanisms for the following sigmatropic shifts

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