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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6:23 minutes

Problem 41

Textbook Question

The mass spectrum of tert-butylamine follows shows an intense base peak at m/z 58, and very little else. Use a diagram to show the cleavage that accounts for the base peak. Suggest why no molecular ion is visible in this spectrum.

Verified step by step guidance

Analyze the mass spectrum provided. The base peak at m/z 58 indicates the most stable and abundant fragment ion formed during the fragmentation of tert-butylamine.

Understand the structure of tert-butylamine: (CH3)3CNH2. The molecule consists of a tert-butyl group ((CH3)3C-) attached to an amine (-NH2). Fragmentation typically occurs at the weakest bond or the most favorable cleavage site.

Propose the cleavage mechanism: The bond between the tert-butyl group and the amine group is likely to break, forming a stable carbocation (C4H10+, m/z 58). This carbocation is stabilized by hyperconjugation and inductive effects from the three methyl groups.

Explain the absence of a molecular ion peak: The molecular ion (m/z 73 for tert-butylamine) is likely absent due to its instability. Tert-butylamine undergoes rapid fragmentation upon ionization, favoring the formation of the stable m/z 58 fragment instead of retaining the molecular ion.

Draw a diagram to illustrate the cleavage: Show the tert-butylamine structure, the bond cleavage between the tert-butyl group and the amine group, and the formation of the stable carbocation (C4H10+, m/z 58). This visual representation helps clarify the fragmentation process.

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Key Concepts

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

Mass Spectrometry

Mass spectrometry is an analytical technique used to measure the mass-to-charge ratio of ions. It involves ionizing chemical species and sorting the resulting ions based on their mass. The output is a mass spectrum, which displays the relative abundance of detected ions at various mass-to-charge (m/z) ratios, providing insights into the molecular structure and composition of the sample.

Base Peak

The base peak in a mass spectrum is the peak with the highest intensity, representing the most abundant ion detected. In the case of tert-butylamine, the base peak at m/z 58 indicates a stable fragment ion resulting from the cleavage of the molecule. Understanding the base peak helps in identifying the most significant fragmentation pathways and the structure of the compound.

Molecular Ion

The molecular ion is the ion that corresponds to the intact molecule of the analyte, typically represented as M+. Its absence in a mass spectrum can indicate that the molecule has fragmented before detection, often due to instability or the presence of weak bonds. In tert-butylamine's spectrum, the lack of a molecular ion suggests that fragmentation occurs readily, leading to the formation of smaller, more stable ions.

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For each of the molecules shown, predict the structure of at least one major fragment in the mass spectrum.

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For each of the molecules shown, predict the structure of at least one major fragment in the mass spectrum.

(b)

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The molecular ion (M) is significant in the mass spectrum of benzyl fluoride, but it is barely present in the mass spectrum of benzyl iodide. Why might this be the case?

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The mass spectrum for a compound with molecular weight of 102 is shown below. Its IR spectrum has a broad, strong absorption at 3600 cm^–1 and a medium absorption at 1360 cm^–1.

a. Identify the compound.

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The following compounds undergo McLafferty rearrangement in the mass spectrometer. Predict the masses of the resulting charged fragments.

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