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 63d
Identify each of the following compounds from its molecular formula and its IR and 1H NMR spectra.
d. C4H8O2
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Verified step by step guidance1
Examine the molecular formula C4H8O2. This indicates the compound has 4 carbons, 8 hydrogens, and 2 oxygens. The degree of unsaturation can be calculated using the formula: (2C + 2 - H)/2. For C4H8O2, the degree of unsaturation is (2(4) + 2 - 8)/2 = 1, suggesting one double bond or ring in the structure.
Analyze the IR spectrum. The broad absorption around 3200-3600 cm⁻¹ indicates the presence of an O-H group, likely from an alcohol or carboxylic acid. The sharp peak near 1700 cm⁻¹ corresponds to a C=O stretch, suggesting the presence of a carbonyl group. Together, these features suggest a carboxylic acid functional group.
Interpret the 1H NMR spectrum. The peak at δ ≈ 2.0 ppm corresponds to hydrogens adjacent to a carbonyl group (likely CH3-C=O). The peaks around δ ≈ 1.0 ppm suggest hydrogens in a methyl group (CH3). The peak at δ ≈ 4.0 ppm indicates hydrogens attached to a carbon bonded to an oxygen atom (likely CH-O).
Combine the IR and NMR data. The IR spectrum suggests a carboxylic acid functional group, while the NMR spectrum indicates the presence of methyl and methylene groups. This aligns with a structure containing a carboxylic acid and alkyl groups.
Propose the structure. Based on the molecular formula, IR, and NMR data, the compound is likely butanoic acid (CH3-CH2-CH2-COOH), which satisfies the molecular formula C4H8O2 and matches the spectral data.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Molecular Formula Interpretation
The molecular formula C4H8O2 indicates that the compound contains four carbon atoms, eight hydrogen atoms, and two oxygen atoms. This information is crucial for determining the possible structural isomers and functional groups present in the compound, which can guide the analysis of its IR and NMR spectra.
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How to interpret condensed structures.
Infrared (IR) Spectroscopy
IR spectroscopy is a technique used to identify functional groups in a molecule based on the absorption of infrared light at specific wavelengths. Key peaks in the IR spectrum for C4H8O2 may indicate the presence of hydroxyl (–OH) or carbonyl (C=O) groups, which are essential for deducing the compound's structure.
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Proton Nuclear Magnetic Resonance (1H NMR) Spectroscopy
1H NMR spectroscopy provides information about the hydrogen atoms in a molecule, including their environment and connectivity. The chemical shifts and splitting patterns observed in the NMR spectrum for C4H8O2 can reveal the number of unique hydrogen environments and help confirm the presence of specific functional groups, aiding in the structural identification of the compound.
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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
Sketch the following spectra that would be obtained for 2-chloroethanol:
a. The 1H NMR spectrum for an anhydrous sample of the alcohol.
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Textbook Question
The 1H NMR spectrum of 2-propen-1-ol is shown here. Indicate the protons in the molecule that are responsible for each of the signals in the spectrum.
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Textbook Question
Draw a splitting diagram for the Hb proton if Jbc = 10 and Jba = 5.
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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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