Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

15. Analytical Techniques:IR, NMR, Mass Spect

1H NMR:Spin-Splitting Simple Tree Diagrams

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

1H NMR:Spin-Splitting Simple Tree Diagrams

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Problem 41

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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First, understand the concept of coupling constants in NMR spectroscopy. The coupling constant, denoted as J, is a measure of the interaction between nuclear spins and is expressed in Hertz (Hz). It provides information about the spatial relationship between coupled nuclei.

Identify the structure of trans-but-2-enoic acid. The trans configuration indicates that the substituents on the double bond are on opposite sides. This affects the coupling constant between the hydrogen atoms Hₐ and H꜀.

Consider the geometry of the molecule. In trans-but-2-enoic acid, Hₐ and H꜀ are on opposite sides of the double bond, which typically results in a larger coupling constant compared to a cis configuration due to the dihedral angle between the protons.

Recall typical values for coupling constants in alkenes. For trans alkenes, the coupling constant is usually in the range of 12-18 Hz. This is due to the larger dihedral angle compared to cis alkenes, which have smaller coupling constants (6-12 Hz).

Justify the expected coupling constant for Hₐ and H꜀ in trans-but-2-enoic acid based on the trans configuration and typical values for coupling constants in similar structures. The trans configuration leads to a larger coupling constant due to the spatial arrangement of the protons.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Coupling Constant

The coupling constant, denoted as J, is a measure of the interaction between nuclear spins in NMR spectroscopy. It is expressed in hertz (Hz) and provides information about the spatial relationship between coupled nuclei. The value of J depends on the number of bonds separating the nuclei and the geometry of the molecule, with larger values typically indicating closer or more direct interactions.

Trans Configuration

In organic chemistry, a trans configuration refers to the arrangement of substituents across a double bond where they are on opposite sides. This configuration affects the coupling constant, as trans protons typically exhibit larger coupling constants compared to cis protons due to the more extended spatial arrangement, which influences the magnetic interaction between them.

NMR Spectroscopy

Nuclear Magnetic Resonance (NMR) spectroscopy is a technique used to determine the structure of organic compounds by observing the magnetic properties of atomic nuclei. In NMR, the chemical environment of hydrogen atoms (protons) is analyzed, providing insights into molecular structure, including the number of hydrogen atoms, their connectivity, and interactions, such as coupling constants, which help deduce spatial arrangements.

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Related Practice

Textbook Question

For the hydrogen(s) screened in blue, draw the signal you would expect to see in a ¹H NMR spectrum. At which chemical shift would the signal appear?

(e)

Textbook Question

Predict the splitting pattern for each of the indicated hydrogens in Assessment 15.59.

(d)

Textbook Question

A chemist made what was thought to be compound A or B. How could coupling constants between H_a and H_b be used to distinguish between the two isomers? [Hint: Draw a chair conformation of each.]

Textbook Question

Draw the expected signal for a hydrogen with the following coupling constants.

(b) Hₐ : δ 3.34 (Jₐ꜀ = 9 , Jₐ₆ = 4 )

Textbook Question

Sketch the signals you would expect to see for Hₐ in the molecule shown. The important coupling constants are given.

Textbook Question

Sketch the signals you would expect to see for H_b in the molecule shown. The important coupling constants are given.

Textbook Question

Sketch the signals you would expect to see for H꜀ in the molecule shown. The important coupling constants are given.

Textbook Question

Draw a diagram like the one shown in Figure 14.12 to predict

a. the relative intensities of the peaks in a triplet.

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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.<IMAGE>

Key Concepts

Coupling Constant

Trans Configuration

NMR Spectroscopy

Watch next

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.
<IMAGE>