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 44
Mullins 1st EditionCh. 14 - Structural Identification I: Infrared Spectroscopy and Mass SpectrometryProblem 44Chapter 13, Problem 44
2-Methylnonan-4-one can undergo two different McLafferty rearrangements. Draw the products of each of them.
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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.
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Definition of Claisen Rearrangement
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.
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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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00:48The definition of hydrogenation.
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
Identify the peaks in the mass spectrum of octan-4-one that correspond to (b) the McLafferty rearrangement.
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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.
(f) C―S vs C=O
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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
Assign the structure based on the mass spectrum and IR spectrum shown.
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