Table of contents

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

Mass Spect:Fragmentation

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

Mass Spect:Fragmentation

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4:18 minutes

Problem 10

Textbook Question

Ethers are not easily differentiated by their infrared spectra, but they tend to form predictable fragments in the mass spectrum. The following compounds give similar but distinctive mass spectra.

Both compounds give prominent peaks at m/z 116, 73, 57, and 43. But one compound gives a distinctive strong peak at 87, and the other compound gives a strong peak at 101. Determine which compound gives the peak at 87 and which one gives the peak at 101. Propose fragmentations to account for the ions at m/z 116, 101, 87, and 73.

Verified step by step guidance

Step 1: Analyze the chemical structures provided in the image. The first compound is ethyl propyl ether (CH3CH2OCH2CH2CH3), and the second compound is methyl butyl ether (CH3OCH2CH2CH2CH3). Both are ethers, and their fragmentation patterns in mass spectrometry will depend on the cleavage of bonds around the oxygen atom.

Step 2: Understand the mass spectrum peaks. The m/z values correspond to the mass-to-charge ratio of fragments. Peaks at m/z 116, 73, 57, and 43 are common to both compounds, indicating similar fragmentation pathways. However, the distinctive peaks at m/z 87 and 101 will help differentiate the compounds.

Step 3: Propose fragmentation for m/z 116. This peak corresponds to the molecular ion of both compounds, representing the intact molecule without fragmentation. For ethyl propyl ether, the molecular ion is CH3CH2OCH2CH2CH3, and for methyl butyl ether, it is CH3OCH2CH2CH2CH3.

Step 4: Propose fragmentation for m/z 87 and m/z 101. The peak at m/z 87 is likely due to the loss of an ethyl group (CH3CH2) from ethyl propyl ether, forming CH3CH2OCH2+. The peak at m/z 101 is likely due to the loss of a methyl group (CH3) from methyl butyl ether, forming CH3OCH2CH2CH2+.

Step 5: Propose fragmentation for m/z 73. This peak is common to both compounds and likely corresponds to the loss of a propyl group (CH2CH2CH3) from ethyl propyl ether or a butyl group (CH2CH2CH2CH3) from methyl butyl ether, forming CH3OCH2+.

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Key Concepts

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

Mass Spectrometry Fragmentation

Mass spectrometry fragmentation involves the breaking of chemical bonds in a molecule to produce smaller ions, which can be detected and analyzed. The pattern of these fragments provides insight into the structure of the original compound. Each compound has a unique fragmentation pattern based on its molecular structure, allowing for differentiation between similar compounds.

Infrared Spectroscopy Limitations

Infrared (IR) spectroscopy is a technique used to identify functional groups in organic compounds based on their vibrational transitions. However, ethers often exhibit similar IR spectra due to their structural similarities, making it challenging to distinguish between them using this method alone. This limitation necessitates the use of complementary techniques, such as mass spectrometry, for more precise identification.

Molecular Ion Peaks

In mass spectrometry, the molecular ion peak corresponds to the intact molecule's mass, while fragment peaks represent the various ions produced during fragmentation. The m/z values of these peaks provide critical information about the molecular structure. For the compounds in question, analyzing the m/z values at 116, 101, 87, and 73 will help determine the specific fragmentation pathways and identify which compound corresponds to each peak.

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Textbook Question

Predict the masses and the structures of the most abundant fragments observed in the mass spectra of the following compounds.

Textbook Question

Predict the masses and the structures of the most abundant fragments observed in the mass spectra of the following compounds.

(b) 3-methylhex-2-ene

Textbook Question

Predict the masses and the structures of the most abundant fragments observed in the mass spectra of the following compounds. (a) 2-methylpentane

Textbook Question

Account for the peaks at m/z 87, 111, and 126 in the mass spectrum of 2,6-dimethylheptan-4-ol.

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Textbook Question

Show the fragmentations that give rise to the peaks at m/z 43, 57, and 85 in the mass spectrum of 2,4-dimethylpentane (Figure 12-17).

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Textbook Question

A laboratory student added 1-bromobutane to a flask containing dry ether and magnesium turnings. An exothermic reaction resulted, and the ether boiled vigorously for several minutes. Then she added acetone to the reaction mixture and the ether boiled even more vigorously. She added dilute acid to the mixture and separated the layers. She evaporated the ether layer, and distilled a liquid that boiled at 143 °C. GC–MS analysis of the distillate showed one major product with a few minor impurities. The mass spectrum of the major product is shown here.

(b) Explain why the molecular ion is or is not visible in the mass spectrum, and show what ions are likely to be responsible for the strong peaks at m/z 59 and 101.

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Textbook Question

Using curved arrows, show the principal fragments you would expect to see in the mass spectrum of each of the following compounds:

Textbook Question

Using curved arrows, show the principal fragments you would expect to see in the mass spectrum of each of the following compounds:

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