A laboratory student was converting cyclohexanol to cyclohexyl bromide by using one equivalent of sodium bromide in a large excess of concentrated sulfuric acid. The major product she recovered was not cyclohexyl bromide, but a compound of formula C 6 H 10 that gave the following 13 C NMR spectrum: <IMAGE> (a) Propose a structure for this product. (b) Assign the peaks in the 13 C NMR spectrum to the carbon atoms in the structure. (c) Suggest modifications in the reaction to obtain a better yield of cyclohexyl bromide.

Hey everyone, Let's do this problem and says a student tried to synthesize some cyclo hexane chloride in the laboratory by reacting cyclo hexane, all which looks like this with one equivalent of sodium chloride in a large excess of concentrated sulfuric acid. Unfortunately the synthesis was not successful. Sounds like my organic chemistry lab and after the synthesis was completed, the student isolated a compound of formula C six H 10. If the carbon 13 NMR spectrum of the compound is shown below, One give a plausible structure for the product to assign all peaks in the carbon, 13 NMR spectrum of the product and three obtain a higher, sorry to obtain a higher yield of cyclo hexane chlorine suggests modifications in the reaction. So we wanted cyclo hexane, cory. But we got this unknown compound with the formula C six H 10. And we want to know that structure. So when we're given the molecular formula and we want to know the structure, we can calculate the index of hydrogen deficiency to give us some clues about the characteristics of the structure. So the formula for I. H. D. Is two times the number of carbons plus two plus the number of nitrogen minus the number of hydrogen is minus the number of halogen, all over two. We only have carbons and hydrogen. So we will have two times the number of carbons which is six plus two minus 10. The number of hydrogen all over two gives us an answer of two. So with that value we know there are either two rings in our structure, Two double bonds, right? Because they each give a value of one. Or we could have one ring And one double bond. A combination of the two. Okay, so let's use our NMR spectrum to try and narrow down what our structure looks like. If we have two rings, two double bonds or one of each. Well we have this signal here after 1 20 between 21 25. And this is actually the signal for an al keen. And there's only one signal. So that means we must have one ring and one double bond. If this represents a double bond then the other I HD value must represent a ring. So we have a ring and a double bond. And I also notice that there are only three signals from my spectrum but there are six carbons in the formula. So if there are three signals in six carbons, that means that my compound is symmetrical and I see that these two signals are for CH two CH two. So that means our structure must look, it must have the formula CH two, CH two and then have our elkin carbon. So if this is half of the structure then the other half Must look like this CH two CH two. But it's a ring. So these end carbons are going to connect which gives us the following structure. Okay, so we have our six carbons and are all keen. Now we also want to label the peaks. So our peak at 1 28 PPm is going to be for RL keen carbon. Then our next signal 25 PPm will be for that CH two carbon closer to the alkaline. In our 23 PPM will be for that other CH two carbon. So we have the structure of our product that was obtained in the signals. Now, for the last part it says, suggest modifications in the reaction so that we can obtain cyclo Hexcel chloride, Right? That's what we wanted to obtain. But we didn't. So, we would have our cyclo hexane all converting to our cyclo Hexcel chloride. And we know that phosphorous tri chloride is one of the best re agents for converting a primary or secondary alcohol to an alcohol chloride. So, this will be a much better re agent to produce this product. And that gives B- two b the correct answer for this problem. That's it for this one. I hope this video is helpful. And thanks 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

15. Analytical Techniques:IR, NMR, Mass Spect

Carbon NMR

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

Carbon NMR

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Problem 31

Textbook Question

A laboratory student was converting cyclohexanol to cyclohexyl bromide by using one equivalent of sodium bromide in a large excess of concentrated sulfuric acid. The major product she recovered was not cyclohexyl bromide, but a compound of formula C₆H₁₀ that gave the following ¹³C NMR spectrum:
<IMAGE>
(a) Propose a structure for this product.
(b) Assign the peaks in the ¹³C NMR spectrum to the carbon atoms in the structure.
(c) Suggest modifications in the reaction to obtain a better yield of cyclohexyl bromide.

Verified step by step guidance

Step 1: Analyze the chemical formula C6H10 provided in the problem. This indicates the compound is unsaturated, as it follows the general formula for alkenes (CnH2n). The presence of double bonds or rings is likely.

Step 2: Examine the 13C NMR spectrum. The peaks at approximately 130 ppm suggest the presence of sp2-hybridized carbons, which are characteristic of double bonds in alkenes. Peaks at lower ppm values (around 20-40 ppm) correspond to sp3-hybridized carbons, likely from alkyl groups.

Step 3: Propose a structure for the compound based on the NMR data. The sp2-hybridized carbons suggest a double bond, and the sp3-hybridized carbons indicate alkyl groups attached to the double bond. A plausible structure is cyclohexene, which matches the formula C6H10 and the NMR data.

Step 4: Assign the peaks in the 13C NMR spectrum to the carbon atoms in cyclohexene. The peak at ~130 ppm corresponds to the two sp2-hybridized carbons in the double bond. The peaks at ~20-40 ppm correspond to the sp3-hybridized carbons in the ring.

Step 5: Suggest modifications to improve the yield of cyclohexyl bromide. To avoid elimination reactions leading to cyclohexene, use milder conditions such as phosphorus tribromide (PBr3) or thionyl bromide (SOBr2) instead of concentrated sulfuric acid, which promotes elimination.

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Key Concepts

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

Nucleophilic Substitution Reactions

Nucleophilic substitution reactions involve the replacement of a leaving group in a molecule by a nucleophile. In the context of converting cyclohexanol to cyclohexyl bromide, the nucleophile (bromide ion) attacks the carbon atom bonded to the hydroxyl group, leading to the formation of the desired product. Understanding this mechanism is crucial for predicting the outcome of the reaction and the potential side products formed.

NMR Spectroscopy

Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. The <sup>13</sup>C NMR spectrum provides information about the number and environment of carbon atoms in a molecule. By analyzing the chemical shifts and splitting patterns in the spectrum, one can deduce the connectivity and arrangement of carbon atoms in the product, which is essential for answering part (b) of the question.

Reaction Conditions and Mechanisms

The conditions under which a reaction occurs can significantly influence the products formed. In this case, the use of concentrated sulfuric acid as a catalyst can lead to dehydration reactions, resulting in the formation of alkenes instead of the desired alkyl bromide. Understanding how to modify reaction conditions, such as using a different solvent or adjusting the concentration of reagents, is key to optimizing the yield of cyclohexyl bromide, as discussed in part (c) of the question.

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