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 40a
Mullins 1st EditionCh. 15 - Structural Identification II: Nuclear Magnetic Resonance SpectroscopyProblem 40aChapter 14, Problem 40a
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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Identify the type of hydrogen environment: The hydrogen Hₐ is located at δ 5.34 ppm, which suggests it is in an alkene or aromatic environment.
Understand the coupling constants: Jₐ꜀ = 12 Hz indicates a trans coupling, typical for alkenes, while Jₐ₆ = 2 Hz suggests a long-range or allylic coupling.
Determine the splitting pattern: The hydrogen Hₐ will be split into a doublet of doublets due to the two different coupling constants.
Draw the signal: Start by drawing a doublet with a splitting of 12 Hz, then split each of these peaks further into doublets with a splitting of 2 Hz.
Label the peaks: Ensure that the peaks are labeled with the correct coupling constants, showing the larger splitting (12 Hz) and the smaller splitting (2 Hz).
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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 5.34 indicates the position of the hydrogen signal on the NMR spectrum.
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11:44
1H NMR Chemical Shifts
Coupling Constant (J)
The coupling constant (J) is a parameter that quantifies the interaction between nuclear spins in NMR spectroscopy, resulting in signal splitting. It is measured in Hertz (Hz) and reflects the strength of spin-spin coupling. Jₐ꜀ = 12 Hz and Jₐ₆ = 2 Hz indicate the splitting pattern of the hydrogen signal due to interactions with neighboring nuclei.
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02:54Sonogashira Coupling Reaction
Signal Multiplicity
Signal multiplicity refers to the number of peaks observed in an NMR signal due to spin-spin coupling. It is determined by the number of neighboring hydrogen atoms and their coupling constants. In this question, the hydrogen signal will be split into a pattern based on the given coupling constants, indicating the presence of adjacent hydrogen atoms.
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Related Practice
Textbook Question
A chemist made what was thought to be compound A or B. How could coupling constants between Ha and Hb be used to distinguish between the two isomers? [Hint: Draw a chair conformation of each.]
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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
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
What coupling constant would you expect between Hₐ and H₆ in cyclopent-2-en-1-one?
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