Textbook Question
The 1H NMR spectra of three isomers with molecular formula C4H9Br are shown here. Which isomer produces which spectrum?
c. <IMAGE>
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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 54a
The 1H NMR spectra of three isomers with molecular formula C4H9Br are shown here. Which isomer produces which spectrum?
a. <IMAGE>
Verified step by step guidance1
Analyze the molecular formula C4H9Br, which indicates the presence of four carbons, nine hydrogens, and one bromine atom. This suggests the compound is an alkyl bromide.
Examine the 1H NMR spectrum provided. The spectrum shows three distinct signals corresponding to three different types of hydrogen environments.
Interpret the signal at approximately 1 ppm labeled as '3 H'. This is likely a methyl group (-CH3) attached to a carbon that is not directly bonded to an electronegative atom, as the chemical shift is low.
Interpret the signal at approximately 2 ppm labeled as '2 H'. This is likely a methylene group (-CH2-) adjacent to the bromine atom, as the chemical shift is slightly deshielded due to the electronegativity of bromine.
Interpret the signal at approximately 0.9 ppm labeled as '6 H'. This suggests two equivalent methyl groups (-CH3) in a symmetrical environment, likely part of an isopropyl group structure. Combine this information to deduce the isomer that matches the spectrum.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
1H NMR Spectroscopy
Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. It provides information about the number of hydrogen atoms in different environments within a molecule, indicated by peaks in the spectrum. The position of these peaks (measured in parts per million, PPM) reveals the electronic environment of the protons, while the area under each peak corresponds to the number of protons contributing to that signal.
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1H NMR Integration
Chemical Shifts
Chemical shifts in 1H NMR spectra are indicative of the electronic environment surrounding hydrogen atoms in a molecule. Different functional groups and molecular structures cause protons to resonate at different frequencies, resulting in distinct chemical shifts. For example, protons adjacent to electronegative atoms or in alkyl chains will appear at different PPM values, allowing chemists to infer structural information about the isomers being analyzed.
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Integration and Multiplicity
Integration in 1H NMR refers to the area under the peaks, which quantifies the number of protons contributing to each signal. Multiplicity, on the other hand, describes the splitting of NMR signals due to neighboring protons (n+1 rule), providing insight into the number of adjacent hydrogen atoms. Together, integration and multiplicity help in deducing the connectivity and arrangement of atoms in the isomers, which is crucial for identifying which spectrum corresponds to each isomer of C4H9Br.
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Related Practice
Textbook Question
How can 1H NMR distinguish between the compounds in each of the following pairs?
g.
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Textbook Question
Answer the following questions:
c. What is the relationship between coupling constant in hertz and operating frequency?
d. How does the operating frequency in NMR spectroscopy compare with the operating frequency in IR and UV/Vis spectroscopy?
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Textbook Question
Identify each of the following compounds from the 1H NMR data and molecular formula:
b. C8H9Br: a 3H doublet at 2.01 ppm a 1H quartet at 5.14 ppm
a 5H broad singlet at 7.35 ppm
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Textbook Question
The 1H NMR spectra of three isomers with molecular formula C4H9Br are shown here. Which isomer produces which spectrum?
b. <IMAGE>
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Textbook Question
Match each of the 1H NMR spectra with one of the following compounds:
b. <IMAGE>
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