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 50
Bruice 8th EditionCh. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis SpectroscopyProblem 50Chapter 14, Problem 50
A mass spectrum shows significant peaks at m/z = 87, 115, 140, and 143. Which of the following compounds is responsible for that mass spectrum?
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Analyze the given m/z values (87, 115, 140, and 143) and consider that these represent the mass-to-charge ratios of fragments in the mass spectrum. Each peak corresponds to a fragment of the molecule, so the task is to deduce the structure of the compound that could produce these fragments.
Determine the molecular formula or structure of the possible compounds provided in the question. If no compounds are explicitly listed, consider common organic molecules that could produce fragments with these m/z values.
For each m/z value, calculate the possible fragment that could correspond to it. For example, m/z = 87 could correspond to a fragment such as C6H11+ (calculated as 6 carbons × 12 + 11 hydrogens × 1 = 87). Repeat this process for m/z = 115, 140, and 143.
Compare the calculated fragments to the possible fragmentation patterns of the candidate compounds. Consider common fragmentation mechanisms such as cleavage at weak bonds, loss of small neutral molecules (e.g., H2O, CO2), or rearrangements.
Match the fragmentation pattern of the compound that best explains all the observed m/z values. The compound whose fragmentation produces peaks at m/z = 87, 115, 140, and 143 is the one responsible for the given 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 provides information about the molecular weight and structure of compounds by generating a mass spectrum, which displays the relative abundance of ions at different mass-to-charge (m/z) values. Understanding how to interpret these peaks is crucial for identifying compounds based on their molecular weights.
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01:25
How to Read a Mass Spectrum
Isotopic Patterns
Isotopic patterns refer to the distribution of isotopes of an element in a compound, which can affect the mass spectrum. For example, elements like carbon and chlorine have naturally occurring isotopes that can create additional peaks in the spectrum. Recognizing these patterns helps in deducing the molecular formula and structure of the compound responsible for the observed peaks.
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08:06Common Splitting Patterns
Fragmentation
Fragmentation is the process by which a molecule breaks apart into smaller ions during mass spectrometry. The resulting fragments can provide insights into the structure of the original compound. Analyzing the m/z values of these fragments allows chemists to piece together the molecular structure and identify the compound that produced the mass spectrum.
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12:08Simple Fragmentation Mechanisms
Related Practice
Textbook Question
a. How could you use IR spectroscopy to determine whether the following reaction had occurred?
b. After purifying the product, how could you determine whether all the NH2NH2 had been removed?
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Textbook Question
A compound gives a mass spectrum with essentially only three peaks at m/z = 77 (40%), 112 (100%), and 114 (33%). Identify the compound.
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Textbook Question
Norlutin and Enovid are ketones that suppress ovulation, so they have been used clinically as contraceptives. For which of these compounds would you expect the infrared carbonyl absorption (C=O stretch) to be at a higher frequency? Explain.
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Textbook Question
What hydrocarbons that contain a six-membered ring will have a molecular ion peak at m/z = 112?
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Textbook Question
Assuming that the force constant is approximately the same for C–C, C–N, and C–O bonds, predict the relative positions of their stretching vibrations in an IR spectrum.
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