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 55b
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
Verified step by step guidance1
Step 1: Analyze the molecular formula C8H9Br. This indicates the compound contains 8 carbons, 9 hydrogens, and 1 bromine atom. The degree of unsaturation can be calculated using the formula: (2C + 2 - H + N - X)/2, where X is the number of halogens. For C8H9Br, the degree of unsaturation is (2(8) + 2 - 9 - 1)/2 = 4, suggesting the presence of aromatic rings or double bonds.
Step 2: Examine the 1H NMR data. The 3H doublet at 2.01 ppm suggests a methyl group adjacent to a CH group, likely part of an ethyl group. The splitting pattern indicates coupling with one neighboring proton.
Step 3: The 1H quartet at 5.14 ppm corresponds to a CH group that is part of an ethyl group. The quartet arises due to coupling with three neighboring protons (the methyl group). This chemical shift suggests the CH group is attached to a bromine atom.
Step 4: The 5H broad singlet at 7.35 ppm is characteristic of an aromatic ring. The singlet indicates that the aromatic ring is monosubstituted, as all five protons resonate together without splitting.
Step 5: Combine the information: The compound has an ethyl group (-CH2-CH3) attached to a bromine atom and a monosubstituted aromatic ring. The structure is consistent with bromomethylbenzene (C6H5-CH2-CH3).
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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, their chemical shifts (ppm), and splitting patterns, which indicate the number of neighboring hydrogen atoms. Understanding these signals helps in deducing the molecular structure and functional groups present in the compound.
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1H NMR Integration
Chemical Shifts and Splitting Patterns
In 1H NMR, chemical shifts are measured in parts per million (ppm) and indicate the electronic environment of hydrogen atoms. The splitting patterns, such as doublets and quartets, arise from the interaction of protons with neighboring protons, following the n+1 rule, where n is the number of neighboring protons. Analyzing these shifts and patterns allows chemists to infer the connectivity and arrangement of atoms in the molecule.
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Molecular Formula Interpretation
The molecular formula provides essential information about the number and types of atoms in a compound. For C8H9Br, the formula indicates the presence of 8 carbon atoms, 9 hydrogen atoms, and 1 bromine atom. This information, combined with NMR data, helps in identifying the specific structure of the compound, as different structural isomers can have the same molecular formula but different NMR spectra.
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Related Practice
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
The 1H NMR spectra of three isomers with molecular formula C4H9Br are shown here. Which isomer produces which spectrum?
b. <IMAGE>
1
views
Textbook Question
The 1H NMR spectra of three isomers with molecular formula C4H9Br are shown here. Which isomer produces which spectrum?
a. <IMAGE>
1
views