Textbook Question
Answer the following questions for each compound:
a. How many signals are in its 13C NMR spectrum?
b. Which signal is at the lowest frequency?
9. CH2=CHBr
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Ch. 14 - NMR 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
Chapter 15, Problem 41a(7)
Answer the following questions for each compound:
a. How many signals are in its 13C NMR spectrum? b. Which signal is at the lowest frequency?
7. 
Verified step by step guidance1
Step 1: Analyze the structure of the compound provided. The molecule is a ketone with two carbonyl groups and a linear alkyl chain. Identify all unique carbon environments in the molecule.
Step 2: Determine the number of unique carbon environments. In 13C NMR spectroscopy, each unique carbon environment corresponds to a distinct signal. Look for symmetry and identical groups to reduce the number of signals.
Step 3: Assign the chemical shifts to each carbon environment. Carbonyl carbons (C=O) typically appear at high frequencies (downfield), while alkyl carbons appear at lower frequencies (upfield). Consider the electronic environment and proximity to electronegative groups.
Step 4: Identify the signal at the lowest frequency. The lowest frequency signal corresponds to the carbon in the least deshielded environment, typically a methyl or methylene group far from electronegative groups or π systems.
Step 5: Summarize the findings. State the total number of signals in the 13C NMR spectrum and specify which carbon corresponds to the lowest frequency signal based on its electronic environment.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
13C NMR Spectroscopy
13C NMR (Nuclear Magnetic Resonance) spectroscopy is a technique used to determine the structure of organic compounds by analyzing the carbon atoms in a molecule. Each unique carbon environment in a compound produces a distinct signal in the NMR spectrum. The number of signals corresponds to the number of different carbon environments, allowing chemists to infer structural information about the compound.
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04:00
13C NMR General Features
Chemical Shifts
Chemical shifts in NMR spectroscopy refer to the resonance frequency of a nucleus relative to a standard in a magnetic field. In 13C NMR, the chemical shift is influenced by the electronic environment surrounding the carbon atom, including electronegative atoms and hybridization. Signals appear at different frequencies, with lower frequency signals typically indicating more shielded environments, such as those near electron-donating groups.
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11:441H NMR Chemical Shifts
Signal Interpretation
Interpreting signals in an NMR spectrum involves analyzing the number of signals, their positions, and their intensities. Each signal corresponds to a unique carbon environment, and the position of the signal indicates the chemical shift. By understanding the structure of the compound, one can predict which signal will appear at the lowest frequency, often associated with carbonyl groups or other electron-withdrawing functionalities.
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02:02Identifying Proton Signals
Related Practice
Textbook Question
Describe the proton-coupled 13C NMR spectra for compound 5 in Problem 41, indicating the relative positions of the signals.
5.
1345
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Textbook Question
Describe the proton-coupled 13C NMR spectra for compound 3 in Problem 41, indicating the relative positions of the signals.
3.
1208
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Textbook Question
Describe the proton-coupled 13C NMR spectra for compound 1 in Problem 41, indicating the relative positions of the signals.
1. CH3CH2CH2Br
1256
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Textbook Question
Propose a mechanism for proton exchange of an alcohol in aqueous base.
685
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Textbook Question
Answer the following questions for each compound:
a. How many signals are in its 13C NMR spectrum?
b. Which signal is at the lowest frequency?
8.
936
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