In addition to radicals, anions, and cations, a fourth class of reactive intermediates is carbenes. A neutral species, the simplest carbene has a molecular formula of CH 2 . (e) Carbenes have great synthetic utility, especially in the synthesis of cyclopropanes from alkenes. Based on your answers to (a)–(d), show a mechanism for the cyclopropanation of cyclohexene.

Welcome back everyone. Carbines with a molecular formula. Ch two are very useful in forming cyclo propane from Alkins determine the mechanism of the given reaction below. The starting material is an lke. We have that double bond present in our structure. We are reacting it with carbine and we are specifically forming a three member cyclo propane ring, right, the two initial hygiene atoms that were implicit in particular, we can expand them. They are now pointing down on two dashes. So they're forming our ring or three member above the plane. So what we want to do in this problem is just draw that mechanism for the given a reaction. Now, the reaction mechanism is very simple. It only requires us to use two arrows because the mechanism is concerted, meaning everything takes place in one single step. So what we're going to do is just draw that reaction arrow and Carbine through that long pair of electrons. And what we're going to show here is that this reactive intermediate will attack the carbon from the pi bond and then the pi bond will essentially attack back forming that three membered rank. And that's it. Our mechanism is ready, we can draw the product. We are breaking the spy bond and we are essentially incorporating ach two group into our product. And of course, just as the problem suggests, we want to make sure that we add those wedges. So let's go ahead and do that. Now, once again, we are not seeing those hydris, but of course, we can expand them because if those carbon atoms are pointing up or specifically, if that carbon atom from the Sieh two group is pointing up, then the implicit hydrogen atoms must be pointing down. So everything is consistent, that will be our final mechanism. And thank you for watching.

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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

10. Addition Reactions

Carbene

Organic Chemistry

10. Addition Reactions

Carbene

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Problem 79e

Textbook Question

In addition to radicals, anions, and cations, a fourth class of reactive intermediates is carbenes. A neutral species, the simplest carbene has a molecular formula of CH₂ .
(e) Carbenes have great synthetic utility, especially in the synthesis of cyclopropanes from alkenes. Based on your answers to (a)–(d), show a mechanism for the cyclopropanation of cyclohexene.

Verified step by step guidance

Understand the structure of a carbene: A carbene is a neutral species with a divalent carbon atom that has two nonbonding electrons. The simplest carbene is methylene (CH₂), which can exist in either a singlet or triplet state. Singlet carbenes have paired electrons, while triplet carbenes have unpaired electrons.

Recognize the reactivity of carbenes: Carbenes are highly reactive intermediates due to their electron deficiency and the presence of nonbonding electrons. They can insert into C-H bonds or react with π-bonds, such as those in alkenes, to form cyclopropanes.

Analyze the reaction: In this case, the carbene will react with cyclohexene, an alkene, to form a cyclopropane ring. The π-electrons of the alkene will interact with the carbene to form two new C-C bonds, resulting in a three-membered cyclopropane ring.

Draw the mechanism: (1) The carbene approaches the double bond of cyclohexene. (2) The π-electrons of the double bond interact with the empty p-orbital of the carbene, while the lone pair of electrons on the carbene forms a bond with the other carbon of the double bond. This concerted reaction forms the cyclopropane ring.

Verify the product: The final product is a cyclopropane derivative of cyclohexene, where the double bond has been replaced by a three-membered ring. Ensure that the stereochemistry of the product is consistent with the reaction conditions and the nature of the carbene (singlet or triplet).

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Key Concepts

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

Carbenes

Carbenes are neutral reactive intermediates that contain a carbon atom with only six valence electrons, making them highly reactive. The simplest carbene, methylene (CH₂), can participate in various chemical reactions, including cyclopropanation. Their unique structure allows them to act as electrophiles, enabling them to add across double bonds in alkenes.

Cyclopropanation

Cyclopropanation is a chemical reaction that involves the formation of a cyclopropane ring from an alkene. This process typically occurs through the addition of a carbene to the double bond of the alkene, resulting in a three-membered ring. The reaction is significant in organic synthesis due to the strain and reactivity of cyclopropanes, which can lead to further transformations.

Reaction Mechanism

A reaction mechanism is a step-by-step description of the pathway taken during a chemical reaction, detailing the formation and transformation of intermediates. Understanding the mechanism of cyclopropanation involves identifying the key steps, such as the generation of the carbene and its subsequent addition to the alkene. This knowledge is crucial for predicting the products and optimizing reaction conditions in synthetic chemistry.

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