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 40b
Mullins 1st EditionCh. 15 - Structural Identification II: Nuclear Magnetic Resonance SpectroscopyProblem 40bChapter 14, Problem 40b
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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Identify the hydrogen atom in question, Hₐ, and note its chemical shift, δ 3.34, which indicates where the signal will appear on the NMR spectrum.
Understand the coupling constants provided: Jₐ꜀ = 9 Hz and Jₐ₆ = 4 Hz. These values indicate the splitting pattern of the signal due to neighboring hydrogens.
Determine the number of neighboring hydrogens that cause the splitting. The coupling constant Jₐ꜀ = 9 Hz suggests a strong coupling with one set of hydrogens, while Jₐ₆ = 4 Hz suggests a weaker coupling with another set.
Predict the splitting pattern based on the coupling constants. A larger coupling constant typically indicates a doublet, while a smaller one might suggest further splitting. Consider the possibility of a doublet of doublets.
Draw the expected NMR signal for Hₐ, showing the splitting pattern as a doublet of doublets, with the larger coupling constant (9 Hz) causing the initial split and the smaller constant (4 Hz) causing further splitting of each peak.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Chemical Shift (δ)
Chemical shift (δ) is a measure of the resonance frequency of a nucleus relative to a standard in a magnetic field. It is expressed in parts per million (ppm) and provides information about the electronic environment surrounding the nucleus. In this question, δ 3.34 indicates the position of the hydrogen signal on the NMR spectrum, suggesting the hydrogen is in a relatively deshielded environment.
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11:44
1H NMR Chemical Shifts
Coupling Constants (J)
Coupling constants (J) are a measure of the interaction between nuclear spins and are expressed in hertz (Hz). They provide information about the number of neighboring hydrogens and their spatial relationship. In this question, Jₐ꜀ = 9 Hz and Jₐ₆ = 4 Hz indicate the hydrogen is coupled to two different sets of neighboring hydrogens, leading to a splitting pattern in the NMR signal.
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NMR Splitting Patterns
NMR splitting patterns arise from spin-spin coupling between non-equivalent hydrogens. The number of peaks in a splitting pattern is determined by the n+1 rule, where n is the number of neighboring hydrogens. In this case, the hydrogen with coupling constants Jₐ꜀ = 9 Hz and Jₐ₆ = 4 Hz will exhibit a complex splitting pattern, reflecting its interactions with two different sets of neighboring hydrogens.
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Related Practice
Textbook Question
Draw the expected signal for a hydrogen with the following coupling constants.
(a) Hₐ : δ 5.34 (Jₐ꜀ = 12 , Jₐ₆ = 2)
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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
Alkene hydrogens usually appear at similar chemical shifts between 5 and 6 ppm. The alkene hydrogens in the structure shown are very different. Rationalize the difference in chemical shifts between Hₐ and H₆ in the structure shown.
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Textbook Question
What coupling constant would you expect between Hₐ and H₆ in cyclopent-2-en-1-one?
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