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

NMR Practice

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

NMR Practice

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6:17 minutes

Problem 45

Textbook Question

Identify pairs of coupled protons in the compound whose COSY spectrum is shown below.
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Verified step by step guidance

Examine the COSY (Correlation Spectroscopy) spectrum provided. COSY is a 2D NMR technique that shows correlations between protons that are scalar (J) coupled. Look for cross-peaks, which indicate coupling between protons.

Identify the diagonal peaks in the COSY spectrum. These represent the chemical shifts of individual protons in the molecule. Each diagonal peak corresponds to a specific proton environment.

Locate the off-diagonal cross-peaks. These cross-peaks indicate coupling between two protons. For example, if a cross-peak appears at the intersection of two chemical shifts, it means the protons corresponding to those shifts are coupled.

Assign the chemical shifts of the diagonal peaks to specific protons in the compound. Use the molecular structure (if provided) and the chemical shift values to determine which protons correspond to each peak.

Match the cross-peaks to the coupled protons. For each cross-peak, identify the two protons that are coupled. These pairs of protons are the coupled protons in the compound. Ensure that the coupling is consistent with the molecular structure and the expected J-coupling patterns.

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Key Concepts

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

COSY Spectroscopy

COSY (Correlation Spectroscopy) is a two-dimensional NMR technique that provides information about the coupling between protons in a molecule. It allows for the identification of which protons are coupled to each other by displaying cross-peaks in the spectrum, indicating interactions. This technique is particularly useful for elucidating the structure of organic compounds by revealing connectivity between protons.

Coupled Protons

Coupled protons are hydrogen atoms in a molecule that interact with each other through scalar coupling, leading to splitting patterns in NMR spectra. The degree of coupling can affect the chemical shifts and multiplicity of the signals observed. Understanding which protons are coupled helps in determining the molecular structure and the spatial arrangement of atoms.

Spin-Spin Coupling

Spin-spin coupling refers to the interaction between the magnetic spins of neighboring nuclei, which results in the splitting of NMR signals. This phenomenon is quantified by the coupling constant (J), which indicates the strength of the interaction. Recognizing the patterns of splitting allows chemists to deduce the number of neighboring protons and their arrangement in the molecule.

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Sonogashira Coupling Reaction

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Related Practice

Textbook Question

When heated with chromic acid, compound A forms benzoic acid. Identify compound A from its ¹H NMR spectrum.

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Textbook Question

Draw the NMR spectrum expected from ethanol that has been shaken with a drop of D₂O.

Textbook Question

Given the ¹H NMR spectrum and the molecular formula, suggest a structure for each molecule. [The IR spectrum suggests the presence of two C=O bonds.]

(a) Important IR bands (cm ⁻ ¹) : 1728, 1708 [Note: The pKₐ of this molecule is around 10.]

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Textbook Question

A small pilot plant was adding bromine across the double bond of but-2-ene to make 2,3-dibromobutane. A controller malfunction allowed the reaction temperature to rise beyond safe limits. A careful distillation of the product showed that several impurities had formed, including the one having the NMR spectra that appear below. Determine its structure, and assign the peaks to the protons in your structure.

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Textbook Question

What does cross peak X in Figure 14.34 tell you?

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Textbook Question

The ¹H NMR spectrum of 2-propen-1-ol is shown here. Indicate the protons in the molecule that are responsible for each of the signals in the spectrum.

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Open Question

Draw the approximate positions that the following compound might show in its 1H NMR absorptions?

Open Question

Draw the approximate positions that the following compound might show in its 1H NMR absorptions?

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Identify pairs of coupled protons in the compound whose COSY spectrum is shown below.<IMAGE>

Key Concepts

COSY Spectroscopy

Coupled Protons

Spin-Spin Coupling

Identify pairs of coupled protons in the compound whose COSY spectrum is shown below.
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