Textbook Question
Which underlined proton (or sets of protons) has the greater chemical shift (that is, the higher frequency signal)?
c.
d.
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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 13a,b
Which underlined proton (or sets of protons) has the greater chemical shift (that is, the higher frequency signal)?
a. 
b. 
Verified step by step guidance1
Step 1: Understand the concept of chemical shift in NMR spectroscopy. Chemical shift is influenced by the electronic environment around a proton. Electronegative atoms or groups deshield the proton, causing a higher chemical shift (downfield signal).
Step 2: Analyze the first pair of protons in part (i). The proton attached to the carbon bonded to chlorine (Cl) is more deshielded compared to the proton attached to the carbon bonded to iodine (I). Chlorine is more electronegative than iodine, pulling electron density away from the proton more effectively.
Step 3: Compare the second pair of protons in part (ii). The proton attached to the carbon bonded to bromine (Br) is less deshielded compared to the proton in the aldehyde group. The aldehyde proton is highly deshielded due to the electron-withdrawing effect of the carbonyl group (C=O).
Step 4: Summarize the findings. In part (i), the proton near chlorine has the greater chemical shift. In part (ii), the aldehyde proton has the greater chemical shift due to the strong deshielding effect of the carbonyl group.
Step 5: Conclude that the chemical shift is determined by the electronegativity and electron-withdrawing effects of nearby atoms or functional groups. This principle can be applied to predict chemical shifts in other molecules.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Chemical Shift in NMR Spectroscopy
Chemical shift refers to the resonance frequency of a nucleus relative to a standard in a magnetic field, typically measured in parts per million (ppm). In proton NMR, the chemical shift is influenced by the electronic environment surrounding the hydrogen atoms. Protons near electronegative atoms or in deshielded environments resonate at higher frequencies, resulting in greater chemical shifts.
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1H NMR Chemical Shifts
Electronegativity and Shielding Effects
Electronegativity is the tendency of an atom to attract electrons towards itself. In NMR, protons attached to carbon atoms adjacent to electronegative atoms (like Cl, Br, or O) experience deshielding, which increases their chemical shift. This means that protons in such environments will resonate at higher frequencies compared to those in more shielded environments, such as those attached to carbon atoms in saturated hydrocarbons.
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Integration and Multiplicity in NMR
Integration in NMR spectroscopy refers to the area under the peaks in the spectrum, which correlates to the number of protons contributing to that signal. Multiplicity indicates the splitting of NMR signals due to neighboring protons, following the n+1 rule, where n is the number of adjacent protons. Understanding these concepts helps in interpreting the NMR spectrum and identifying the environment of specific protons.
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Related Practice
Textbook Question
If two signals differ by 1.5 ppm in a 300 MHz spectrometer, by how much do they differ in a 500 MHz spectrometer?
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Textbook Question
Without referring to Table 14.1, label the proton or set of protons in each compound that gives the signal at the lowest frequency a, at the next lowest b, and so on.
h.
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Textbook Question
Without referring to Table 14.1, label the proton or set of protons in each compound that gives the signal at the lowest frequency a, at the next lowest b, and so on.
e.
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Textbook Question
Without referring to Table 14.1, label the proton or set of protons in each compound that gives the signal at the lowest frequency a, at the next lowest b, and so on.
c. ClCH2CH2CH2Cl
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Textbook Question
If two signals differ by 90 Hz in a 300 MHz spectrometer, by how much do they differ in a 500 MHz spectrometer
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