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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Problem 62e

Textbook Question

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

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Identify the molecular ion peak (M+) in the mass spectrum, which corresponds to the molecular weight of the compound. This peak is crucial for determining the possible fragments.

Consider the stability of potential carbocations that can form upon fragmentation. More stable carbocations (e.g., tertiary > secondary > primary) are more likely to appear as major fragments.

Look for common fragmentation patterns such as alpha cleavage, where a bond adjacent to a heteroatom or functional group is broken, leading to a stable cation and a neutral radical.

Consider the possibility of rearrangements, such as the McLafferty rearrangement, which involves a six-membered transition state and is common in carbonyl-containing compounds.

Analyze the mass-to-charge (m/z) ratios of the observed peaks in the spectrum to match them with possible fragment structures, taking into account isotopic patterns and the presence of elements like chlorine or bromine, which have characteristic isotope peaks.

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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 helps identify the composition of a sample by generating a mass spectrum, which displays the masses of fragments. Understanding how molecules break apart and form ions is crucial for predicting the major fragments in a mass spectrum.

Fragmentation Patterns

Fragmentation patterns in mass spectrometry refer to the predictable ways in which molecules break apart into smaller ions. These patterns depend on the structure and stability of the molecule, with certain bonds more likely to break. Recognizing common fragmentation pathways, such as alpha cleavage or McLafferty rearrangement, aids in predicting major fragments.

Stability of Carbocations

The stability of carbocations plays a significant role in determining fragmentation patterns. More stable carbocations, such as tertiary over secondary or primary, are more likely to form during fragmentation. Understanding the factors that stabilize carbocations, like hyperconjugation and resonance, helps predict which fragments will be prominent in the mass spectrum.

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Related Practice

Textbook Question

In the mass spectrum of hexan-3-ol, identify the fragments arising from two α-cleavage fragmentations and one dehydration fragmentation.

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Textbook Question

Suggest three ways that the following tertiary amine can fragment by α-cleavage. At which m/z would you expect to see peaks corresponding to these fragments?

Textbook Question

The base peak in Figure 14.51 has m/z 45. Suggest a molecular formula and a structure for this fragment.

<IMAGE>

Textbook Question

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

(d)

Textbook Question

Identify the peaks in the mass spectrum of octan-4-one that correspond to (a) α-cleavage.

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Textbook Question

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

(b)

Textbook Question

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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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.

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

Key Concepts

Mass Spectrometry

Fragmentation Patterns

Stability of Carbocations

Watch next

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