Textbook Question
The 1H NMR spectra of three isomers with molecular formula C7H14O are shown here. Which isomer produces which spectrum?
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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 58
Would it be better to use 1H NMR or 13C NMR spectroscopy to distinguish 1-butene, cis-2-butene, and 2-methylpropene? Explain your answer.
Verified step by step guidance1
Step 1: Understand the structural differences between the three compounds: 1-butene, cis-2-butene, and 2-methylpropene. These differences will influence the number and type of signals observed in both 1H NMR and 13C NMR spectroscopy.
Step 2: Analyze the 1H NMR spectra. In 1H NMR, the number of unique hydrogen environments and their splitting patterns (due to spin-spin coupling) can help distinguish the compounds. For example, 1-butene has terminal hydrogens on the double bond, while cis-2-butene has hydrogens in a cis configuration, and 2-methylpropene has a methyl group attached to the double bond.
Step 3: Analyze the 13C NMR spectra. In 13C NMR, the number of unique carbon environments is determined by the symmetry of the molecule. For instance, 1-butene has four unique carbon environments, cis-2-butene has three due to its symmetry, and 2-methylpropene has three unique carbons as well.
Step 4: Compare the advantages of each technique. 1H NMR provides detailed information about hydrogen environments and coupling patterns, which can be useful for distinguishing compounds with different hydrogen arrangements. On the other hand, 13C NMR focuses on carbon environments and is less affected by splitting patterns, making it easier to count unique carbons in symmetric molecules.
Step 5: Conclude which technique is better. Since the compounds differ significantly in their carbon environments (e.g., number and symmetry), 13C NMR would be more straightforward for distinguishing these compounds. However, 1H NMR could also be used if detailed splitting patterns and chemical shifts are analyzed carefully.
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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 exploits the magnetic properties of certain nuclei, such as hydrogen (1H) and carbon (13C), to provide information about the number and environment of these atoms in a molecule. The resulting spectra reveal distinct signals that correspond to different chemical environments, allowing chemists to deduce structural information.
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General NMR Features
1H NMR vs. 13C NMR
1H NMR focuses on the hydrogen atoms in a molecule, providing detailed information about the number of hydrogen environments and their connectivity. In contrast, 13C NMR targets carbon atoms, offering insights into the carbon skeleton and the types of functional groups present. The choice between the two depends on the specific structural features one aims to analyze, with 1H NMR often being more sensitive to subtle differences in hydrogen environments.
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Isomer Distinction
Isomers are compounds with the same molecular formula but different structural arrangements. In the case of 1-butene, cis-2-butene, and 2-methylpropene, their distinct arrangements lead to different chemical environments for hydrogen and carbon atoms. 1H NMR is particularly effective in distinguishing these isomers due to its sensitivity to the spatial arrangement of hydrogen atoms, which can reveal differences in stereochemistry and connectivity.
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Related Practice
Textbook Question
An alkyl halide reacts with an alkoxide ion to form a compound whose 1H NMR spectrum is shown here. Identify the alkyl halide and the alkoxide ion. (Hint: See Section 9.15.)
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Textbook Question
Compound A, with molecular formula C4H9Cl, shows two signals in its 13C NMR spectrum. Compound B, an isomer of compound A, shows four signals, and in the proton-coupled mode, the signal farthest downfield is a doublet. Identify compounds A and B.
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Textbook Question
Identify each of the following compounds from the 1H NMR data and molecular formula:
c. C5H10O2: a 3H triplet at 1.15 ppm
a 3H triplet at 1.25 ppm
a 2H quartet at 2.33 ppm
a 2H quartet at 4.13 ppm
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Textbook Question
Identify the compound with molecular formula C7H14O that gives the following proton-coupled 13C NMR spectrum:
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Textbook Question
Identify each of the following compounds from its molecular formula and its IR and 1H NMR spectra:
b. C6H12O2
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