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 44
Mullins 1st EditionCh. 15 - Structural Identification II: Nuclear Magnetic Resonance SpectroscopyProblem 44Chapter 14, Problem 44
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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Identify the structure of acetone: Acetone is a simple ketone with the formula (CH₃)₂CO. It consists of a central carbonyl group (C=O) flanked by two methyl groups (CH₃).
Understand the concept of deuterium substitution: Deuterium (D) is an isotope of hydrogen with one neutron. Replacing hydrogen atoms with deuterium in a molecule can affect its NMR properties.
Determine the positions of Hₐ and H₆ in acetone: In acetone, the hydrogens on the methyl groups are equivalent due to the symmetry of the molecule. Therefore, Hₐ and H₆ refer to any of the hydrogens on the methyl groups.
Consider the symmetry and equivalence in acetone: When you replace Hₐ and H₆ with deuterium, the symmetry of the molecule means that the two products are identical. This is because the methyl groups are equivalent and the substitution does not break the symmetry.
Predict the NMR signals: In ¹H NMR, equivalent hydrogens give rise to a single signal. Since the two hydrogens (Hₐ and H₆) are equivalent in acetone, replacing them with deuterium will not change this equivalence. Therefore, you would expect these hydrogens to give one signal in the ¹H NMR spectrum.
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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 another isotope of the same element, 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.
Chemical Equivalence in NMR
Chemical equivalence in NMR refers to the condition where nuclei in a molecule experience the same electronic environment, resulting in a single signal in the NMR spectrum. In acetone, the two hydrogens (Hₐ and H₆) are chemically equivalent, meaning they are in identical environments and would typically produce one signal in the ¹H NMR spectrum.
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NMR Spectroscopy
NMR spectroscopy is a technique used to determine the structure of organic compounds by analyzing the magnetic properties of atomic nuclei. In ¹H NMR, the number of signals corresponds to the number of distinct hydrogen environments in a molecule. Isotopic substitution, such as replacing hydrogen with deuterium, can alter the NMR signals due to changes in the magnetic environment.
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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, 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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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
Sketch the signals you would expect to see for H꜀ in the molecule shown. The important coupling constants are given.
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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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