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 43b

Textbook Question

Identify the peaks in the mass spectrum of octan-4-one that correspond to (b) the McLafferty rearrangement.
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Verified step by step guidance

Understand the McLafferty rearrangement: This is a reaction in mass spectrometry where a molecule undergoes a rearrangement involving the transfer of a hydrogen atom and the cleavage of a bond, typically resulting in a neutral molecule and a radical cation.

Identify the structure of octan-4-one: Octan-4-one is a ketone with the formula C8H16O. The carbonyl group is located at the fourth carbon in the chain.

Locate the gamma hydrogen: In the McLafferty rearrangement, a hydrogen atom three carbons away from the carbonyl group (gamma position) is involved. For octan-4-one, identify the gamma hydrogen relative to the carbonyl group.

Illustrate the rearrangement: Draw the mechanism showing the transfer of the gamma hydrogen to the carbonyl oxygen, resulting in the cleavage of the bond between the alpha and beta carbons, forming a double bond and a neutral alkene molecule.

Determine the mass of the resulting fragments: Calculate the mass of the radical cation and the neutral alkene formed from the McLafferty rearrangement. These masses correspond to the peaks you would observe in the mass spectrum.

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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 interpreting these spectra.

McLafferty Rearrangement

The McLafferty rearrangement is a specific fragmentation pattern observed in mass spectrometry, particularly in carbonyl compounds. It involves a hydrogen atom transfer from a gamma-carbon (three carbons away from the carbonyl group) to the carbonyl oxygen, followed by cleavage of the bond between the alpha and beta carbons, resulting in a stable enol and a neutral alkene.

Fragmentation Patterns

Fragmentation patterns in mass spectrometry refer to the specific ways in which a molecule breaks apart into smaller ions. These patterns are influenced by the structure of the molecule and the stability of the resulting fragments. Recognizing these patterns, such as the McLafferty rearrangement, is essential for deducing the structure of the original compound from its mass spectrum.

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Related Practice

Textbook Question

An unknown compound gives the following mass, IR, and NMR spectra. Propose a structure, and show how it is consistent with the spectra. Show the fragmentations that give the prominent peaks at m/z 127 and 155 in the mass spectrum.

Textbook Question

A student added 3-phenylpropanoic acid (PhCH₂CH₂COOH) to a molten salt consisting of a 1:1 mixture of NaCl and AlCl₃ maintained at 170 °C. After 5 minutes, he poured the molten mixture into water and extracted it into dichloromethane. Evaporation of the dichloromethane gave a 96% yield of the product whose spectra follow. The mass spectrum of the product shows a molecular ion at m/z 132. What is the product?

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Textbook Question

Why were no products from the McLafferty rearrangement observed in the spectrum of butan-2-one (Figure 18-3)?

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Textbook Question

Identify the compound that gives the mass spectrum and infrared spectrum shown here.

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Textbook Question

2-Methylnonan-4-one can undergo two different McLafferty rearrangements. Draw the products of each of them.

Textbook Question

In the mass spectrum of the following compounds, which is the tallest—the peak at m/z = 57 or the peak at m/z = 71?

a. 3-methylpentane

b. 2-methylpentane

Textbook Question

What hydrocarbons that contain a six-membered ring will have a molecular ion peak at m/z = 112?

Textbook Question

Assign the structure based on the mass spectrum and IR spectrum shown.

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Identify the peaks in the mass spectrum of octan-4-one that correspond to (b) the McLafferty rearrangement.<IMAGE>

Key Concepts

Mass Spectrometry

McLafferty Rearrangement

Fragmentation Patterns

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Identify the peaks in the mass spectrum of octan-4-one that correspond to (b) the McLafferty rearrangement.
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