Textbook Question
Explain the relative chemical shifts of the benzene ring protons in Figure 14.18.
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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 22b
Draw a diagram like the one shown in Figure 14.12 to predict
b. the relative intensities of the peaks in a quintet.
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Verified step by step guidance1
Understand the concept of spin-spin splitting: In NMR spectroscopy, the splitting of a signal into multiple peaks (multiplets) occurs due to the interaction of the magnetic moments of neighboring nuclei. A quintet indicates that the nucleus being observed is coupled to four equivalent neighboring nuclei.
Apply the (n+1) rule: The number of peaks in a multiplet is determined by the number of equivalent neighboring protons (n) plus one. For a quintet, n = 4, so the signal splits into 5 peaks.
Determine the relative intensities using Pascal's triangle: The relative intensities of the peaks in a quintet follow the coefficients of the fifth row of Pascal's triangle, which are 1:4:6:4:1. These coefficients represent the relative heights of the peaks.
Draw the diagram: Sketch five peaks on the x-axis (chemical shift axis) with relative heights corresponding to the coefficients 1:4:6:4:1. Ensure the peaks are symmetrically distributed around the central peak.
Label the diagram: Clearly label the x-axis as the chemical shift (δ, in ppm) and indicate the relative intensities of the peaks. This will help in visualizing the quintet pattern and understanding its structure.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nuclear Magnetic Resonance (NMR) Spectroscopy
NMR spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. It relies on the magnetic properties of certain nuclei, primarily hydrogen (1H) and carbon (13C), to provide information about the number of neighboring atoms and their environments. The resulting spectrum displays peaks that correspond to different chemical environments, allowing chemists to infer structural details.
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General NMR Features
Spin-Spin Coupling
Spin-spin coupling, or J-coupling, occurs when the magnetic fields of neighboring nuclei influence each other, leading to the splitting of NMR signals into multiple peaks. The number of peaks and their relative intensities in a multiplet, such as a quintet, is determined by the number of neighboring protons (n) according to the n+1 rule. This concept is crucial for interpreting the complexity of NMR spectra and understanding molecular connectivity.
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Relative Peak Intensities
In NMR spectroscopy, the relative intensities of peaks in a multiplet provide insight into the number of equivalent protons contributing to each signal. For a quintet, the intensity pattern follows a binomial distribution, reflecting the probability of different spin states among neighboring protons. Understanding how to predict and calculate these intensities is essential for accurately interpreting NMR spectra and deducing structural information.
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Related Practice
Textbook Question
Draw a diagram like the one shown in Figure 14.12 to predict
a. the relative intensities of the peaks in a triplet.
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Textbook Question
Indicate the number of signals and the multiplicity of each signal in the 1H NMR spectrum of each of the following compounds:
a. CH3CH2CH2CH2CH2CH3
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Textbook Question
Which of the following compounds is responsible for the 1H NMR spectrum shown below?
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Textbook Question
Explain how the following compounds, each with the same molecular formula, could be distinguished by their 1H NMR spectra.
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Textbook Question
Indicate the number of signals and the multiplicity of each signal in the 1H NMR spectrum of each of the following compounds:
c. ClCH2CH2CH2Cl
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