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 62d

Textbook Question

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

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Identify the molecular ion peak in the mass spectrum, which corresponds to the molecular weight of the compound. This peak is often the highest m/z value in the spectrum.

Consider the possible fragmentation patterns based on the structure of the molecule. Common fragmentation patterns include cleavage at the weakest bonds, such as C-C or C-H bonds, and the formation of stable cations.

Analyze the structure of the molecule to identify any functional groups or structural features that might lead to specific fragmentation patterns. For example, alcohols often lose a water molecule, while carbonyl compounds can undergo McLafferty rearrangement.

Predict the formation of a major fragment by considering the stability of the resulting cation. More stable cations, such as tertiary carbocations or resonance-stabilized ions, are more likely to appear as major fragments.

Use the predicted fragmentation pattern to identify the m/z value of the major fragment. This involves calculating the mass of the fragment and considering any isotopic patterns that might be present.

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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 refer to the specific ways in which a molecule breaks apart into smaller ions during mass spectrometry. These patterns are influenced by the molecule's structure, such as the presence of functional groups and bond strengths. Recognizing common fragmentation pathways, like alpha cleavage or McLafferty rearrangement, aids in predicting major fragments.

Stability of Carbocations

The stability of carbocations plays a significant role in determining the major fragments in mass spectrometry. More stable carbocations are more likely to form, influencing the fragmentation pattern. Factors such as hyperconjugation, resonance, and inductive effects contribute to carbocation stability, guiding predictions of which fragments will be most prominent.

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Propose a fragmentation to account for each numbered peak in the mass spectrum of n-butyl isopropyl ether.

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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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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?

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

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

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.
(d)