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

Hello everyone. Let's do this problem. It reads which of the three isomers with the molecular formula C five H C L two has the following proton in M R spectrum, we are given our spectrum and three answer choices. Answer choice A is 24. All right. So how can we use the characteristics of our spectrum to determine our structure? We can break it apart by different characteristics? I like to do so in the following order. So first, we can look at the number of signals produced in our spectrum and compare that to the number of signals that would be produced by our answer choices. Then we can do the same with the integration which represents how many hydrogens are shown in that signal. Then we can look at the multiplicity which tells us how many neighboring hydrogens we have because we use the expression N plus one where N is the number of neighboring protons and that'll show up in our spectrum as a doublet triplet singlet, et cetera. Lastly, we can look at the chemical shift of the signal and that is determined by the relative position of the hydrogen in the structure to, let's say electron negative groups in the structure such as chlorine or oxygen or double bonds. When a proton is next to that electron withdrawing group, it makes a proton electron poor or more naked or DeShields, which will make it have a higher chemical shift. All right. So let's look at each structure and first, we'll look at how many signals each structure will produce. So, starting with structure. A I noticed this structure is symmetrical, which is important because then we will only have half of the signals that we would have if we didn't count the symmetry of the compound. So we will have signal A for these end methyl groups, signal B for the second carbon in and signal C for that central carbon or the proton on that central carbon rather. So that produces three signals, our spectrum also has three signals. So that's a potential match. All right, let's keep going. Structure B will give us signals. So that is incorrect because we know our spectrum will only give us three signals and structure C will give us 12345 signals as well. So once again, just by process of elimination, by number of signals, we know that A is going to be our correct answer. Choice. If you want to stick around, I will go into the other characteristics. So moving on to integration, let's look at signal A, we have six protons signal B will be 12 protons and signal C will also be two protons. Let's look at our spectrum. Yep, we have three signals six H two H two H. So we're still on the right track. Now, let's go to multiplicity. So we have to consider the symmetry here. So we only count one side. So our six H signal signal A will have one neighboring proton, one plus one is two. So that will be a double it. Signal B has 12345 neighboring protons. So that will be a sex tit signal C has one, two neighboring protons. So that will be a triplet and that matches our spectrum, right? Six H doublet, two H triplet and two H sextet. And lastly, let's look at chemical shift. So signal B that carbon is directly attached to the chlorine atom. So those are going to be the most downfield proton signals H B or two H six te, which makes sense, right? That's what we see in our spectrum, which signal will be the least downfield or the most upfield are six H double it, right? Because those six protons are furthest from those chlorine atoms, right? Well, they're the same distance as signal C but notice how the methyl groups have more hydrogens per, per carbon and that is going to make it more shielded. So that will be the most upfield signal, which is what we see in our spectrum. And that will leave signal C in between. All right. So once again, structure A is the correct answer for this problem. That's it for this one. I hope this video is helpful and I'll see you soon.

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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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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
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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 54c

Textbook Question

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

Examine the 1H NMR spectrum provided. The spectrum shows three distinct signals corresponding to different proton environments. The integration values are labeled as 2H, 2H, and 6H, which represent the relative number of protons in each environment.

Interpret the chemical shift values. The signal at approximately 3.5 ppm corresponds to protons near an electronegative atom, likely the bromine. The signal at around 1.8 ppm corresponds to protons in a slightly deshielded environment, such as those adjacent to a carbon-bromine bond. The signal at approximately 1.0 ppm corresponds to protons in a typical alkyl environment.

Consider the splitting patterns. The signal at 3.5 ppm appears as a multiplet, indicating coupling with adjacent protons. The signal at 1.8 ppm also shows splitting, suggesting coupling with nearby protons. The signal at 1.0 ppm appears as a singlet, indicating no coupling with adjacent protons.

Based on the integration, chemical shifts, and splitting patterns, deduce the structure of the isomer that matches this spectrum. The integration of 6H suggests the presence of two equivalent methyl groups, while the 2H signals correspond to protons in distinct environments near the bromine atom and the alkyl chain.

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Key Concepts

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

Nuclear Magnetic Resonance (NMR) Spectroscopy

NMR spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. It relies on the magnetic properties of certain nuclei, primarily hydrogen (1H), to provide information about the number of hydrogen atoms in different environments within a molecule. The resulting spectrum displays peaks corresponding to these environments, allowing chemists to infer structural details.

Chemical Shift

Chemical shift refers to the position of a peak in an NMR spectrum, measured in parts per million (ppm). It indicates the electronic environment surrounding the hydrogen atoms, influenced by factors such as electronegativity and hybridization. Different isomers will exhibit distinct chemical shifts due to variations in their molecular structures, making this a key aspect for identifying isomers in NMR analysis.

Integration in NMR

Integration in NMR spectroscopy quantifies the area under each peak in the spectrum, which correlates to the number of hydrogen atoms contributing to that signal. This allows chemists to determine the relative number of protons in different environments, aiding in the identification of isomers. For example, if a peak integrates to 6H, it indicates that six hydrogen atoms are in that specific environment, providing crucial information for structural elucidation.

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

Key Concepts

Nuclear Magnetic Resonance (NMR) Spectroscopy

Chemical Shift

Integration in NMR

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