Unlike hydroboration–oxidation, the addition of H 2 O catalyzed by H 3 O + is not stereospecific. Thinking carefully about the mechanism of the reaction, give two reasons why.

All right. Hi everyone. So for this question, it says that in contrast to hydro bora oxidation, acid catalyzed hydration of all keens is not stereo specific provide two reasons why so recalled stereo specificity, right. It has to do with the formation of different isomeric reaction products and to understand the stereo chemical result, right, we have to understand how both mechanisms proceed in these cases. So let's start first and foremost with hydration oxidation. Now recall that hydro operation oxidation is the anti Marconi co addition of a hydroxy group, meaning that the less substituted carbon of the All keen is what's going to take that hydroxy group right now. Here it's important to recognize that hydro beration oxidation is a sin addition and the mechanism itself is concerted. And what I mean by that is that the hydrogen of one carbon and the hydroxy group of the other carbon are adding to the same face of the alkene. And this process, this attachment so to speak is happening at the same time because the same intermediate is going to attach itself to both carbons at the same time. So here, right, the stereo specificity has to do with the fact that the addition is both sin and concerted. So let's compare that with acid catalyzed hydration because in acid catalyzed hydration, right, recall that the first step is the formation of a car followed by nucleic attack. So the mechanism here is not concerted, right? Because one step is happening and it's being followed by another step. So already, right, the formation of the carbo CAD ion is already a big factor as to why hydration here is not stereo specific specific because here's the thing, right? Carbos are sp two hybridized, which means that they're cleaner. And if the intermediate is plainer, the nucleic attack can take place either above or below the plant, right, either above or below the carbo ion itself. So that's already one reason. OK. So just to write it out on the bottom here, the first reason is that the nuclei, the nuclear file could attack or add itself on either side, on either side of the cleaner carbo catt ion intermediate. So that's one reason, right? But the second reason has to do with the fact that hydration oxidation is concerted. Whereas acid catalyzed hydration is not because like I said before, right, the same intermediate is adding on to both carbons of the all keen at the same time. So those two factors create a cyclic intermediate. It creates a sort of ring structure that prevents re rotation, right? It prevents free rotation because those two carbons are kind of locked into that ring structure in the intermediate. But the same cannot be said for acid catalyzed hydration. Because after the formation of the carbo CAD ion in acid catalyzed hydration, right, rotation of the bond between the carbo CAD ion and the adjacent carbon is definitely possible. Right. So because of that re rotation before nucleic attack is another reason why this reaction here is not stereo specific. So my second reason is that the bond between the carbo ion and the adjacent carbon could rotate prior to nuclear attack and there you have it. So the two reasons are as follows. The first reason as to why acid catalyzed hydration is not stereo specific is because the nuclear file could add on either side of the planar Carbocaine intermediate. And the second reason is because the bond between the Carbocaine and the adjacent carbon could rotate prior to nucleic attack, which is going to change the stereo chemical outcome even more. Right? So with that being said, thank you so much for watching. And I hope you found this helpful.

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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

Hydroboration

Organic Chemistry

10. Addition Reactions

Hydroboration

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6:46 minutes

Problem 56

Textbook Question

Unlike hydroboration–oxidation, the addition of H₂O catalyzed by H₃O⁺ is not stereospecific. Thinking carefully about the mechanism of the reaction, give two reasons why.

Verified step by step guidance

Understand the mechanism of H₂O addition catalyzed by H₃O⁺: This reaction proceeds via an electrophilic addition mechanism where the alkene reacts with H₃O⁺ to form a carbocation intermediate. The carbocation is planar and sp² hybridized, which is key to understanding the lack of stereospecificity.

Reason 1: The carbocation intermediate formed during the reaction is achiral and planar. This allows the nucleophile (H₂O) to attack from either side of the plane with equal probability, leading to the formation of both enantiomers or diastereomers if applicable. This contrasts with hydroboration–oxidation, which involves a concerted mechanism that is stereospecific.

Reason 2: The reaction does not involve a concerted mechanism like hydroboration–oxidation. Instead, the reaction proceeds stepwise, with the formation of an intermediate carbocation. The lack of a concerted mechanism means there is no control over the stereochemistry of the product.

Compare with hydroboration–oxidation: In hydroboration–oxidation, the addition of H and OH occurs in a single step (concerted mechanism), ensuring syn addition and stereospecificity. The absence of such a concerted mechanism in H₃O⁺-catalyzed hydration explains the lack of stereospecificity.

Conclude: The planar nature of the carbocation intermediate and the stepwise mechanism are the two main reasons why the addition of H₂O catalyzed by H₃O⁺ is not stereospecific.

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Key Concepts

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

Mechanism of Electrophilic Addition

Electrophilic addition involves the attack of an electrophile on a nucleophile, leading to the formation of a carbocation intermediate. In the case of H₂O addition catalyzed by H₃O⁺, the reaction proceeds through a planar carbocation, allowing nucleophilic attack from either side. This lack of preference for one face over the other results in a mixture of stereoisomers, making the reaction non-stereospecific.

Carbocation Stability and Rearrangement

Carbocations are positively charged species that can undergo rearrangements to form more stable structures. During the addition of H₂O in the presence of H₃O⁺, the carbocation can rearrange to a more stable form before the nucleophilic attack occurs. This potential for rearrangement further complicates the stereochemical outcome, as different pathways can lead to different products.

Stereospecificity vs. Stereoselectivity

Stereospecificity refers to reactions where the configuration of the reactant directly determines the configuration of the product, leading to a single stereoisomer. In contrast, stereoselectivity allows for the formation of multiple stereoisomers, with one being favored. The addition of H₂O in the presence of H₃O⁺ is stereoselective rather than stereospecific, as it can yield both enantiomers due to the non-preferential attack on the planar carbocation.

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