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 37
Mullins 1st EditionCh. 14 - Structural Identification I: Infrared Spectroscopy and Mass SpectrometryProblem 37Chapter 13, Problem 37
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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Verified step by step guidance1
Identify the structure of hexan-3-ol: It is a six-carbon chain alcohol with the hydroxyl group (-OH) on the third carbon. The molecular formula is C6H14O.
Understand α-cleavage: In mass spectrometry, α-cleavage involves breaking the bond adjacent to the carbon bearing the functional group. For hexan-3-ol, this means breaking the C-C bonds adjacent to the carbon with the -OH group.
Perform the first α-cleavage: Break the bond between the second and third carbon atoms. This results in a fragment with a positive charge on the second carbon, forming a C2H5+ ion and a neutral fragment.
Perform the second α-cleavage: Break the bond between the third and fourth carbon atoms. This results in a fragment with a positive charge on the third carbon, forming a C3H7+ ion and a neutral fragment.
Consider dehydration fragmentation: Dehydration involves the loss of a water molecule (H2O) from the alcohol. In hexan-3-ol, this typically occurs by removing the hydroxyl group and a hydrogen from an adjacent carbon, resulting in the formation of an alkene fragment with a double bond.
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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 in a mass spectrometer is crucial for interpreting the spectrum and identifying molecular fragments.
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α-Cleavage
α-Cleavage in mass spectrometry involves the breaking of a bond adjacent to a functional group, such as an alcohol group in hexan-3-ol. This process results in the formation of a radical and a cation. Identifying the specific bonds that undergo α-cleavage helps determine the resulting fragments in the mass spectrum.
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Dehydration Fragmentation
Dehydration fragmentation is a common reaction in mass spectrometry for alcohols, where a water molecule (H2O) is eliminated. This process typically results in the formation of an alkene. Recognizing dehydration is essential for identifying the characteristic mass loss of 18 amu, corresponding to the removal of water, in the mass spectrum.
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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
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 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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