Textbook Question
The 1H NMR spectra of three isomers with molecular formula C4H9Br 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 55c
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
Verified step by step guidance1
Analyze the molecular formula C5H10O2. The degree of unsaturation can be calculated using the formula: (2C + 2 - H)/2. Substituting the values, (2(5) + 2 - 10)/2 = 1. This indicates one degree of unsaturation, which could correspond to a double bond or a ring.
Interpret the 1H NMR data. A 3H triplet at 1.15 ppm suggests a methyl group (-CH3) adjacent to a -CH2- group. Similarly, a 3H triplet at 1.25 ppm also suggests another methyl group adjacent to a -CH2- group.
The 2H quartet at 2.33 ppm indicates a -CH2- group adjacent to a carbonyl group (C=O), as this chemical shift is characteristic of protons near an electron-withdrawing group like a carbonyl.
The 2H quartet at 4.13 ppm suggests a -CH2- group adjacent to an electronegative atom, such as oxygen in an ester functional group (-COO-).
Combine the information. The molecular formula, degree of unsaturation, and NMR data suggest the compound is an ester with the structure CH3CH2COOCH2CH3. Verify this by matching the NMR data to the proposed structure.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
NMR Spectroscopy
Nuclear Magnetic Resonance (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 connectivity, and the overall molecular structure. The chemical shifts, multiplicity, and integration of peaks in the NMR spectrum help identify functional groups and the arrangement of atoms.
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General NMR Features
Chemical Shifts
Chemical shifts in NMR spectroscopy refer to the resonance frequency of a nucleus relative to a standard in a magnetic field, measured in parts per million (ppm). Different chemical environments cause shifts in the resonance frequency, allowing chemists to infer the types of hydrogen atoms present. For example, protons attached to electronegative atoms or in different hybridization states will resonate at different ppm values.
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Multiplicity and Integration
Multiplicity in NMR refers to the splitting of NMR signals due to spin-spin coupling between neighboring hydrogen atoms, which provides insight into the number of adjacent protons. Integration indicates the relative number of protons contributing to a particular signal, allowing for the determination of the ratio of different types of hydrogen in the molecule. Together, these concepts help deduce the structure of the compound based on the observed peaks.
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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
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.
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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
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>
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