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 41

Textbook Question

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

Understand that the base peak in a mass spectrum represents the most abundant ion, and its m/z value is crucial for deducing the structure of the fragment.

The m/z value of 45 suggests a fragment with a molecular weight of 45. Consider common organic fragments that could have this mass.

Calculate possible molecular formulas that sum to a molecular weight of 45. For example, consider C3H9N (molecular weight: 3*12 + 9*1 + 14 = 45) or C2H5O (molecular weight: 2*12 + 5*1 + 16 = 45).

Evaluate the chemical plausibility of each formula by considering typical fragmentation patterns in mass spectrometry. For instance, C2H5O could represent an ethoxy group, which is a common fragment.

Propose a structure for the fragment based on the plausible molecular formula. For example, if C2H5O is considered, the structure could be an ethoxy group (CH3CH2O).

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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 (m/z) of ions. It helps identify the composition of a sample by analyzing the mass of its fragments. The base peak represents the most abundant ion, providing clues about the structure of the molecule.

Fragmentation Patterns

Fragmentation patterns in mass spectrometry refer to the way molecules break apart into smaller ions. Understanding these patterns is crucial for deducing the structure of the original molecule. The m/z value of a fragment can suggest possible molecular formulas and structural components.

Molecular Formula Determination

Determining a molecular formula involves calculating the possible combinations of atoms that match the observed m/z value. This requires knowledge of atomic masses and common molecular fragments. For m/z 45, potential fragments could include C3H9N or C2H5O, guiding the identification of the structure.

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Textbook Question

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.

b. Show the mechanism for formation of the peak at m/z = 84.

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Textbook Question

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

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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

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

(d)

Textbook Question

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

(e)

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)

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

Key Concepts

Mass Spectrometry

Fragmentation Patterns

Molecular Formula Determination

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