Textbook Question
Identify the hydrocarbon that has a molecular ion with an m/z value of 128, a base peak with an m/z value of 43, and significant peaks with m/z values of 57, 71, and 85.
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Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblem 13a
Bruice 8th EditionCh. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblem 13aChapter 14, Problem 13a
The mass spectra of 1-methoxybutane, 2-methoxybutane, and 2-methoxy-2-methylpropane are shown below. Match each compound with its spectrum.
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Analyze the molecular structure of each compound (1-methoxybutane, 2-methoxybutane, and 2-methoxy-2-methylpropane) to identify key features that could influence fragmentation patterns in mass spectrometry. For example, consider the position of the methoxy group (-OCH₃) and the branching of the carbon chain.
Understand the general principles of mass spectrometry: molecules are ionized, and the resulting ions fragment in predictable ways. Look for characteristic peaks in the spectra, such as the molecular ion peak (M⁺), base peak (most intense peak), and other significant fragment peaks.
For 1-methoxybutane, predict the fragmentation pattern. The methoxy group is attached to the first carbon, so cleavage near this group may produce a fragment with a mass corresponding to CH₃O⁺ (31 m/z) and another fragment corresponding to the remaining alkyl chain.
For 2-methoxybutane, the methoxy group is attached to the second carbon. This structure may lead to fragmentation that produces a peak for CH₃O⁺ (31 m/z) and other fragments resulting from cleavage at the adjacent carbons, such as a peak for a secondary carbocation.
For 2-methoxy-2-methylpropane, the highly branched structure and the methoxy group on a tertiary carbon will influence fragmentation. Expect a strong molecular ion peak (M⁺) and significant peaks for tertiary carbocations or other stable fragments. Match these predicted patterns to the spectra to identify each compound.
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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 involves ionizing chemical species and sorting the ions based on their mass. The resulting mass spectrum provides information about the molecular weight and structure of the compounds, allowing for the identification of different substances based on their fragmentation patterns.
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Isomerism
Isomerism refers to the phenomenon where compounds have the same molecular formula but different structural arrangements or spatial orientations. In the case of 1-methoxybutane, 2-methoxybutane, and 2-methoxy-2-methylpropane, understanding their structural differences is crucial for interpreting their mass spectra, as these variations can lead to distinct fragmentation patterns.
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Fragmentation Patterns
Fragmentation patterns are the specific ways in which a molecule breaks apart into smaller ions during mass spectrometry. Each compound has a unique fragmentation pattern based on its structure, which can be analyzed to deduce the original molecule. Recognizing these patterns is essential for matching the compounds to their respective mass spectra in the given question.
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Related Practice
Textbook Question
Primary alcohols have a strong peak at m/z = 31.
a. What fragment is responsible for this peak?
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Textbook Question
Can a high-resolution mass spectrometer distinguish between them?
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Textbook Question
Predict the relative intensities of the molecular ion peak, the M+2 peak, and the M+4 peak for a compound that contains two bromine atoms.
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Textbook Question
Using curved arrows, show the principal fragments you would expect to see in the mass spectrum of each of the following compounds:
b.
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Textbook Question
Using curved arrows, show the principal fragments you would expect to see in the mass spectrum of each of the following compounds:
c.
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