Textbook Question
Which of the bonds shown in red are expected to have IR-active stretching frequencies?
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Ch. 12 - Infrared Spectroscopy and Mass Spectrometry
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 12, Problem 4
Spectra are given for three compounds. Each compound has one or more of the following functional groups: alcohol, amine, ketone, aldehyde, and carboxylic acid. Determine the functional group(s) in each compound, and assign the major peaks above 1600 cm–1.
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Verified step by step guidance1
Step 1: Review the IR (Infrared) spectra provided for each compound. Focus on the region above 1600 cm-1, as this is where functional group vibrations typically appear.
Step 2: Identify the characteristic peaks for each functional group. For example: Alcohols (O-H stretch) appear as a broad peak around 3200-3600 cm-1, Amines (N-H stretch) appear as sharp peaks around 3300-3500 cm-1, Ketones (C=O stretch) appear as a sharp peak around 1700-1750 cm-1, Aldehydes (C=O stretch and C-H stretch) show a peak around 1700-1750 cm-1 and additional peaks near 2700-2900 cm-1, and Carboxylic Acids (O-H stretch and C=O stretch) show a broad peak around 2500-3300 cm-1 and a sharp peak around 1700-1750 cm-1.
Step 3: Match the observed peaks in the spectra to the characteristic peaks of the functional groups. For example, if you see a broad peak around 3200-3600 cm-1, it suggests the presence of an alcohol group.
Step 4: Assign the functional group(s) to each compound based on the peaks identified. For instance, if a compound shows a sharp peak around 1700-1750 cm-1 and no broad peak around 3200-3600 cm-1, it likely contains a ketone group.
Step 5: Summarize the functional groups identified for each compound and list the major peaks above 1600 cm-1 that correspond to these groups. Ensure that all peaks are accounted for and consistent with the functional groups assigned.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Infrared Spectroscopy (IR)
Infrared spectroscopy is a technique used to identify functional groups in organic compounds by measuring the absorption of infrared light. Different functional groups absorb IR radiation at characteristic wavelengths, allowing chemists to deduce the presence of specific groups based on the peaks observed in the spectrum.
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General Features of IR Spect
Functional Groups
Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. Common functional groups include alcohols, amines, ketones, aldehydes, and carboxylic acids, each with distinct IR absorption patterns that help in their identification.
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Peak Assignments in IR Spectra
In IR spectra, peaks above 1600 cm-1 are typically associated with the stretching vibrations of bonds in functional groups. For example, carbonyl groups (C=O) in ketones and aldehydes show strong absorption around 1700 cm-1, while O-H stretches in alcohols and carboxylic acids appear around 3200-3600 cm-1, providing critical information for functional group identification.
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Related Practice
Textbook Question
Show the fragmentations that give rise to the peaks at m/z 43, 57, and 85 in the mass spectrum of 2,4-dimethylpentane (Figure 12-17).
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Textbook Question
Identify which of these four mass spectra indicate the presence of sulfur, chlorine, bromine, iodine, or nitrogen. Suggest a molecular formula for each.
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Textbook Question
The infrared spectra for three compounds are provided. Each compound has one or more of the following functional groups: conjugated ketone, ester, amide, nitrile, and alkyne. Determine the functional group(s) in each compound, and assign the major peaks above 1600 cm–1.
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