The 1 H NMR spectra of three isomers with molecular formula C 4 H 9 Br are shown here. Which isomer produces which spectrum? b. <IMAGE>

Hello everyone. Let's solve this problem together. It says which of the three isomers with the molecular formula C five H eight C L two has the following proton. In M R spectrum. We are given the spectrum and three answer choices. Answer choice A is the structure of E and structure C is Z 23, Di Chloro pent two E. So how can we use our spectrum to match our structure? Well, we can look at different characteristics of our proton N M R spectrum and see if they match what would be produced by the structure given to us. So first, we can look at the number of signals will our isomer produce the same number of signals shown in the given spectrum. Then if it is given to us, we can look at the integration we are not given the specific amount of protons that are integrated for each signal. So we'll skip over that for this problem. But I thought it was worth mentioning, then we can look at the multiplicity of each signal. So how many protons are neighboring the proton in question? And that will tell us if our signal is a singlet, doublet triplet, et cetera. And lastly, we can look at the chemical shift. So if a proton is close to an electron dense group, like a chlorine atom or a double bond, as we see in our answer choices that proton is going to be more d shielded or more downfield in our spectrum, right? It'll have a higher chemical shift. So let's look at each of these characteristics in the given answer choices, starting with the number of signals that would be produced. So answer choice, A, we'll produce one, 23 signals. Well, our spectrum has four signals. So we know that this is not a correct answer choice. We can eliminate answer choice. A answer choice B will produce 1234 signals. OK. And answer choice C will produce 123 signals. So answer choice C can be eliminated. And just by that simple process of elimination, we already determine that B is our correct answer for this problem. If you want to stick around, I will go through the other characteristics as well. So moving on to multiplicity in choice A or sorry proton signal A has three hydrogens. Oh That's integration. We wanna look at multiplicity. So there are no neighboring protons for signal A. So that will produce a singlet signal B has two neighboring protons. So that will produce a triplet signal C has 123 neighboring protons. So that will produce a quartet and answer choice Oh my gosh, signal D has 12 neighboring protons. So that will produce a triplet. All right. And that matches our spectrum, right? We have a triplet, a triplet, a quartet and a singlet. All right. So now let's match the chemical shift, right? See if the chemical shift that we see in our spectrum matches what is shown in the structure. So based on our multiplicity, we would have from most downfield to most upfield signal, we would have signal D signal B, signal C and signal A. So looking at our structure signal D those protons are closest to the chlorine atom, right, they share a carbon with the chlorine atom. So that definitely makes sense why those are the most downfield and D shielded protons, right? Then we have signal B those protons are shared by the carbon that is in the double bond. So they are right attached to the double bond. So that makes sense why those protons are also more DeShields. Then we have proton C. OK. Those are between the double bond and the chlorine, they're still a little bit far away. Signal A is adjacent to a chlorine and double bond. Hm. Well, we see that their signals are close signal C those are only two protons on one carbon where signal A has three protons on one carbon. And usually if there are less protons on that carbon, they are going to be more de shielded. So that makes sense why signal C is a little more downfield than signal A. So once again, answer choice B is the correct answer for this problem. That's it for this one. I hope this video was helpful 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
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10. Addition Reactions3h 19m
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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
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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

NMR Practice

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

NMR Practice

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Problem 54b

Textbook Question

The ¹H NMR spectra of three isomers with molecular formula C₄H₉Br are shown here. Which isomer produces which spectrum?
b. <IMAGE>

Verified step by step guidance

Analyze the molecular formula C4H9Br, which indicates the presence of four carbons, nine hydrogens, and one bromine atom. This suggests the possibility of structural isomers such as 1-bromobutane, 2-bromobutane, and 2-methyl-2-bromopropane.

Examine the 1H NMR spectrum provided. Note the chemical shift values (in ppm), the splitting patterns (multiplets, doublets, singlets, etc.), and the relative integration of the peaks, which correspond to the number of protons in each environment.

Identify the peak near 3-4 ppm, which is characteristic of protons attached to a carbon bonded to a bromine atom. This region helps distinguish the position of the bromine in the molecule.

Look at the splitting patterns and chemical shifts of the peaks in the 0-2 ppm region. These peaks correspond to alkyl protons and provide information about the branching and connectivity of the carbon chain.

Match the observed spectrum to the expected NMR patterns for each isomer. For example, 1-bromobutane will show a triplet for the CH3 group, a multiplet for the CH2 groups, and a distinct peak for the CH2-Br group. Similarly, 2-bromobutane and 2-methyl-2-bromopropane will have unique splitting patterns and chemical shifts based on their structures.

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Key Concepts

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

1H NMR Spectroscopy

Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. It provides information about the number of hydrogen atoms in different environments within a molecule, indicated by peaks in the spectrum. The position of these peaks, measured in parts per million (PPM), reflects the electronic environment surrounding the hydrogen atoms, allowing chemists to infer structural details.

Chemical Shifts

Chemical shifts in 1H NMR spectra refer to the specific PPM values at which the peaks appear, influenced by the electronic environment of the hydrogen atoms. Different functional groups and molecular structures cause variations in these shifts, helping to identify the presence of specific groups such as alkyl, aromatic, or halogenated carbons. Understanding chemical shifts is crucial for interpreting the spectrum and correlating it with the corresponding isomer.

Integration of Peaks

The integration of peaks in a 1H NMR spectrum indicates the relative number of hydrogen atoms contributing to each signal. The area under each peak is proportional to the number of protons in that environment, allowing for the determination of the ratio of different types of hydrogen in the molecule. This information is essential for distinguishing between isomers, as it helps to confirm the molecular structure based on the integration values.

The 1H NMR spectra of three isomers with molecular formula C4H9Br are shown here. Which isomer produces which spectrum?b. <IMAGE>

Key Concepts

1H NMR Spectroscopy

Chemical Shifts

Integration of Peaks

The ¹H NMR spectra of three isomers with molecular formula C₄H₉Br are shown here. Which isomer produces which spectrum?
b. <IMAGE>