Textbook Question
Though it wasn't discussed, what coupling constant would you expect for Hₐ and H꜀ in the spectrum of trans-but-2-enoic acid in Figure 15.50? Justify your answer.
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Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
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Mullins 1st EditionCh. 15 - Structural Identification II: Nuclear Magnetic Resonance SpectroscopyProblem 43
Mullins 1st EditionCh. 15 - Structural Identification II: Nuclear Magnetic Resonance SpectroscopyProblem 43Chapter 14, Problem 43
Replace Hₐ, H₆, and H꜀ in methyl benzene with a deuterium. What is the relationship between the three products you obtain? Based on this, how many signals would you expect for these hydrogens in the ¹H NMR spectrum?
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Identify the structure of methyl benzene, also known as toluene. It consists of a benzene ring with a methyl group (CH₃) attached to it.
Recognize that Hₐ, H₆, and H꜀ refer to different hydrogen atoms on the benzene ring. In toluene, these hydrogens are located at different positions relative to the methyl group: ortho (Hₐ), meta (H₆), and para (H꜀).
Replace each of these hydrogens with deuterium (D), which is an isotope of hydrogen. This results in three different deuterated toluene molecules: ortho-deuterated, meta-deuterated, and para-deuterated toluene.
Determine the relationship between the three deuterated products. Since the benzene ring is symmetrical, the ortho, meta, and para positions are chemically distinct, leading to different chemical environments for each deuterium substitution.
Predict the number of signals in the ¹H NMR spectrum. Each unique chemical environment for the hydrogens in the original toluene will result in a separate signal. Consider the symmetry and the effect of the methyl group on the chemical shift of each hydrogen position.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Isotopic Substitution
Isotopic substitution involves replacing an atom in a molecule with its isotope, such as replacing hydrogen (H) with deuterium (D). This substitution can affect the physical and chemical properties of the molecule, including its behavior in spectroscopic analysis, due to the difference in mass between isotopes.
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Understanding the hydrogen isotopes.
NMR Spectroscopy
Nuclear Magnetic Resonance (NMR) Spectroscopy is a technique used to observe the local environment of nuclei in a molecule. In ¹H NMR, hydrogen atoms in different chemical environments produce distinct signals. The number of signals corresponds to the number of unique hydrogen environments in the molecule.
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Chemical Equivalence
Chemical equivalence refers to atoms or groups in a molecule that are in identical environments and thus indistinguishable by NMR. In methyl benzene, the symmetry of the molecule can lead to some hydrogens being chemically equivalent, resulting in fewer NMR signals than the total number of hydrogens.
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Related Practice
Textbook Question
Sketch the signals you would expect to see for Hb in the molecule shown. The important coupling constants are given.
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Textbook Question
Replace Hₐ and H₆ in hexane with a deuterium. What is the relationship between the two products you obtain? Based on this, would you expect the two hydrogens to give one or two signals in the ¹H NMR spectrum?
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Textbook Question
Replace Hₐ and H₆ in acetone with a deuterium. What is the relationship between the two products you obtain? Based on this, would you expect the two hydrogens to give one or two signals in the ¹H NMR spectrum?
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Textbook Question
Draw the expected signal for a hydrogen with the following coupling constants.
(b) Hₐ : δ 3.34 (Jₐ꜀ = 9 , Jₐ₆ = 4 )
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Textbook Question
Sketch the signals you would expect to see for Hₐ in the molecule shown. The important coupling constants are given.
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