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 39
Mullins 1st EditionCh. 14 - Structural Identification I: Infrared Spectroscopy and Mass SpectrometryProblem 39Chapter 13, Problem 39
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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Identify the structure of the tertiary amine. A tertiary amine has three alkyl groups attached to the nitrogen atom. Determine the specific alkyl groups present in the given amine structure.
Understand α-cleavage: In mass spectrometry, α-cleavage refers to the breaking of the bond adjacent to the nitrogen atom in amines. This results in the formation of a radical and a cation. Identify the bonds adjacent to the nitrogen atom that can undergo cleavage.
For each α-cleavage possibility, draw the structure of the resulting fragments. This involves breaking the bond between the nitrogen and the adjacent carbon atom, leading to the formation of a nitrogen-centered radical and a carbon-centered cation.
Calculate the m/z (mass-to-charge ratio) for each fragment. The m/z value is determined by the mass of the fragment divided by its charge. Since the fragments are typically singly charged, the m/z value is equal to the mass of the fragment.
Predict the m/z peaks: Based on the calculated m/z values for each fragment, predict the m/z peaks you would expect to see in the mass spectrum. These peaks correspond to the fragments formed by α-cleavage.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Tertiary Amine Structure
A tertiary amine is an organic compound where a nitrogen atom is bonded to three alkyl or aryl groups. Understanding its structure is crucial for predicting fragmentation patterns, as the nitrogen's lone pair can influence bond cleavage and stability of resulting fragments.
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α-Cleavage in Mass Spectrometry
α-Cleavage refers to the breaking of a bond adjacent to a functional group, such as the nitrogen in amines. This process is significant in mass spectrometry as it helps identify the structure of the compound by generating characteristic fragments, which can be detected and analyzed based on their mass-to-charge ratio (m/z).
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Mass-to-Charge Ratio (m/z)
The mass-to-charge ratio (m/z) is a key parameter in mass spectrometry, representing the mass of a fragment divided by its charge. Peaks in a mass spectrum correspond to specific m/z values, allowing for the identification of fragments resulting from α-cleavage, and providing insights into the molecular structure of the original compound.
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Related Practice
Textbook Question
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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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
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 hexan-3-ol, identify the fragments arising from two α-cleavage fragmentations and one dehydration fragmentation.
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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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