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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Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
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Mullins 1st EditionCh. 14 - Structural Identification I: Infrared Spectroscopy and Mass SpectrometryProblem 35
Mullins 1st EditionCh. 14 - Structural Identification I: Infrared Spectroscopy and Mass SpectrometryProblem 35Chapter 13, Problem 35
Besides the molecular mass, how do you know that the fragment that gives rise to the peak at m/z 111 in the mass spectrum for 1-bromo-4-chlorobenzene contains only chlorine?
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Understand that the mass spectrum provides information about the fragments of a molecule based on their mass-to-charge ratio (m/z). Each peak corresponds to a fragment of the original molecule.
Recognize that 1-bromo-4-chlorobenzene contains both bromine and chlorine atoms, which can influence the mass spectrum due to their isotopic patterns.
Recall that chlorine has two common isotopes: Cl-35 and Cl-37. The presence of these isotopes can create a characteristic pattern in the mass spectrum, typically a peak and a smaller peak two units higher (due to Cl-37).
Consider the isotopic pattern of bromine, which also has two isotopes: Br-79 and Br-81. This results in a distinct pattern with peaks separated by two m/z units, similar to chlorine but with different relative intensities.
Analyze the peak at m/z 111. If this peak corresponds to a fragment containing only chlorine, it should exhibit the characteristic chlorine isotopic pattern without the additional pattern that would be expected if bromine were present. This can be confirmed by the absence of a corresponding peak that would indicate the presence of bromine isotopes.
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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 generating a mass spectrum, which displays the mass of fragments. Understanding how to interpret these spectra is crucial for identifying molecular fragments and their compositions.
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How to Read a Mass Spectrum
Isotopic Patterns
Isotopic patterns arise from the presence of isotopes, which are atoms of the same element with different numbers of neutrons. Chlorine, for example, has two common isotopes, Cl-35 and Cl-37, which create a distinct pattern in mass spectra. Recognizing these patterns helps determine the presence of specific elements in a fragment.
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Fragmentation in Mass Spectrometry
Fragmentation occurs when a molecule breaks into smaller pieces during mass spectrometry. Each fragment corresponds to a peak in the mass spectrum. Understanding the typical fragmentation patterns of compounds, such as the loss of halogens, aids in deducing which elements are present in a specific fragment.
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Related Practice
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?
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Textbook Question
The molecule that gave the mass spectrum shown here contains a halogen. Which halogen is present?
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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
The presence of what atom is indicated by the following mass spectrum?
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Textbook Question
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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