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 43b
Mullins 1st EditionCh. 14 - Structural Identification I: Infrared Spectroscopy and Mass SpectrometryProblem 43bChapter 13, Problem 43b
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 guidance1
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.
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How to Read a Mass Spectrum
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.
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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
Identify the peaks in the mass spectrum of octan-4-one that correspond to (a) α-cleavage.
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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
Based on Hooke's law, choose the bond in each pair that you expect to vibrate at a higher wavenumber.
(e) C=N vs C≡N
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Textbook Question
2-Methylnonan-4-one can undergo two different McLafferty rearrangements. Draw the products of each of them.
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Textbook Question
Assign the structure based on the mass spectrum and IR spectrum shown.
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