Textbook Question
Rank the following compounds from highest wavenumber to lowest wavenumber for their C=O absorption band:
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Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblem 58b
Bruice 8th EditionCh. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblem 58bChapter 14, Problem 58b
The mass spectrum for a compound with molecular weight of 102 is shown below. Its IR spectrum has a broad, strong absorption at 3600 cm–1 and a medium absorption at 1360 cm–1.
b. Show the mechanism for formation of the peak at m/z = 84.
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Analyze the molecular weight of the compound (102) and the IR spectrum data. The broad, strong absorption at 3600 cm⁻¹ suggests the presence of an -OH group (alcohol or phenol). The medium absorption at 1360 cm⁻¹ indicates possible C-H bending vibrations, often associated with methyl groups.
Identify the base structure of the compound. Given the molecular weight and functional group information, hypothesize a structure that includes an alcohol group (-OH) and possibly a methyl group.
Determine the fragment responsible for the m/z = 84 peak. Subtract the mass of the fragment lost from the molecular ion (102 - 84 = 18). A mass of 18 corresponds to the loss of a water molecule (H₂O), which is common in alcohol-containing compounds.
Propose a mechanism for the formation of the m/z = 84 peak. The loss of H₂O can occur via a dehydration reaction. This involves the -OH group and a hydrogen atom from a neighboring carbon atom, forming a double bond in the process. Use curved arrows to show the movement of electrons: (1) the lone pair on the oxygen of the -OH group abstracts a proton, (2) the bond between the oxygen and carbon breaks, and (3) a double bond forms between adjacent carbons.
Verify the stability of the resulting fragment (m/z = 84). The fragment should be a stable carbocation or neutral molecule, depending on the specific structure of the compound. Ensure that the proposed mechanism aligns with the observed mass spectrum and IR data.
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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 molecular weight of compounds and their fragmentation patterns. In this context, the peak at m/z = 84 indicates a specific fragment of the original molecule, which can provide insights into its structure and functional groups.
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01:25
How to Read a Mass Spectrum
Infrared (IR) Spectroscopy
Infrared spectroscopy is a technique that measures the absorption of infrared light by a compound, providing information about its molecular vibrations and functional groups. The broad absorption at 3600 cm–1 suggests the presence of an -OH group, while the medium absorption at 1360 cm–1 may indicate a C-H bending vibration, which can help deduce the compound's structure.
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16:04General Features of IR Spect
Fragmentation Mechanism
Fragmentation mechanisms describe how a molecule breaks apart during mass spectrometry, leading to the formation of smaller ions. Understanding these mechanisms is crucial for interpreting mass spectra, as they reveal how specific fragments, like the one at m/z = 84, are generated from the parent compound, often involving the cleavage of certain bonds or the loss of functional groups.
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12:08Simple Fragmentation Mechanisms
Related Practice
Textbook Question
The IR spectrum of compound A with a molecular formula of C5H12O is shown below. Compound A is oxidized to give compound B, a ketone with a molecular formula of C5H10O. When compound A is heated with H2SO4, compounds C and D are obtained. Considerably more D is obtained than C. Reaction of compound C with O3, followed by treatment with dimethyl sulfide, gives two products: formaldehyde and compound E, with a molecular formula of C4H8O. Reaction of compound D with O3, followed by treatment with dimethyl sulfide, gives two products: compound F, with a molecular formula of C3H6O, and compound G, with a molecular formula of C2H4O. What are the structures of compounds A through G?
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Textbook Question
Which one of the following five compounds produced the IR spectrum shown below?
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Textbook Question
Rank the following compounds from highest wavenumber to lowest wavenumber for their C-O absorption band:
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Textbook Question
The mass spectrum for a compound with molecular weight of 102 is shown below. Its IR spectrum has a broad, strong absorption at 3600 cm–1 and a medium absorption at 1360 cm–1.
a. Identify the compound.
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Textbook Question
Each of the IR spectra shown below is accompanied by a set of four compounds. In each case, indicate which of the four compounds is responsible for the spectrum.
a.
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