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 44

Textbook Question

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

Verified step by step guidance

Identify the structure of 2-Methylnonan-4-one. It is a ketone with a methyl group on the second carbon and a ketone group on the fourth carbon of a nonane chain.

Understand the McLafferty rearrangement: It involves a six-membered cyclic transition state where a hydrogen atom three carbons away from the carbonyl group is transferred to the oxygen, resulting in a double bond and cleavage of the molecule.

Locate the possible gamma (γ) hydrogens relative to the carbonyl group in 2-Methylnonan-4-one. These are the hydrogens on the third and fifth carbons from the carbonyl carbon.

For the first McLafferty rearrangement, consider the γ-hydrogen on the third carbon. This will lead to a cleavage between the third and fourth carbons, forming a product with a double bond between the second and third carbons and a separate fragment containing the carbonyl group.

For the second McLafferty rearrangement, consider the γ-hydrogen on the fifth carbon. This will lead to a cleavage between the fifth and sixth carbons, forming a product with a double bond between the fourth and fifth carbons and a separate fragment containing the carbonyl group.

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Key Concepts

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

McLafferty Rearrangement

The McLafferty rearrangement is a mass spectrometry fragmentation process where a molecule undergoes a specific rearrangement involving a six-membered transition state. Typically, it involves the transfer of a hydrogen atom from a gamma position relative to a carbonyl group, resulting in the cleavage of a bond and formation of an enol and an alkene. Understanding this mechanism is crucial for predicting the fragmentation pattern of carbonyl-containing compounds.

Carbonyl Group

A carbonyl group consists of a carbon atom double-bonded to an oxygen atom (C=O). It is a key functional group in organic chemistry, found in aldehydes, ketones, carboxylic acids, and their derivatives. The carbonyl group is highly polar, making it reactive and a common site for chemical reactions, such as nucleophilic additions and rearrangements like the McLafferty rearrangement.

Gamma Hydrogen

In organic chemistry, a gamma hydrogen refers to a hydrogen atom located on the third carbon atom away from a functional group, such as a carbonyl group. In the context of the McLafferty rearrangement, the presence of a gamma hydrogen is essential as it participates in the hydrogen transfer that initiates the rearrangement process, leading to the formation of specific fragmentation products.

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Related Practice

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

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

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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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Textbook Question

Give the structure of the molecule that gives rise to the following IR and mass spectra.

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