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 Integration

Organic Chemistry

15. Analytical Techniques:IR, NMR, Mass Spect

NMR Integration

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3:14 minutes

Problem 50

Textbook Question

Determine the ratios of the chemically nonequivalent protons in a compound if the steps of the integration curves measure 40.5, 27, 13, and 118 mm, from left to right across the spectrum. Draw the structure of a compound whose ¹H NMR spectrum would show these integrals in the observed order.

Verified step by step guidance

Step 1: Analyze the integration curve values provided (40.5 mm, 27 mm, 13 mm, and 118 mm). These values represent the relative areas under the peaks in the 1H NMR spectrum, which correspond to the number of chemically nonequivalent protons in the molecule.

Step 2: Divide each integration value by the smallest value (13 mm) to normalize the ratios. This will give the relative number of protons contributing to each peak.

Step 3: Identify the chemical environment of the protons in the molecule. For example, in alcohols, the hydroxyl (-OH) group typically appears as a singlet, while alkyl groups contribute to multiplets depending on their connectivity and neighboring groups.

Step 4: Based on the normalized ratios, assign the peaks to specific groups of protons in the molecule. For instance, a CH3 group contributes 3 protons, a CH2 group contributes 2 protons, and a CH group contributes 1 proton.

Step 5: Draw the structure of a compound that matches the observed integration ratios and chemical environments. For example, a molecule like 2-methyl-1-propanol or 1-butanol could fit the given data, depending on the exact proton environments.

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Key Concepts

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

Integration in NMR Spectroscopy

Integration in NMR spectroscopy refers to the area under the peaks in the spectrum, which correlates to the number of protons contributing to that signal. The height or area of each peak is proportional to the number of chemically equivalent protons in the molecule. By measuring these areas, one can determine the relative ratios of different types of protons in the compound.

Chemically Nonequivalent Protons

Chemically nonequivalent protons are protons that are in different chemical environments within a molecule, leading to distinct NMR signals. These differences arise from variations in the electronic environment surrounding the protons, which can be influenced by factors such as electronegativity of nearby atoms and molecular geometry. Understanding which protons are nonequivalent is crucial for interpreting NMR spectra accurately.

Chemical Structure and NMR Interpretation

The chemical structure of a compound directly influences its NMR spectrum, as the arrangement of atoms affects the magnetic environment of protons. Drawing the correct structure based on integration values requires knowledge of how different functional groups and molecular frameworks contribute to the observed signals. For instance, the presence of an alcohol group can lead to specific shifts and integrations in the NMR spectrum, which must be considered when deducing the compound's structure.

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Related Practice

Textbook Question

Complete the table of ¹H NMR data you'd generate for each of the following molecules.

(c)

Textbook Question

Complete the table of ¹H NMR data you'd generate for each of the following molecules.

(d)

Textbook Question

Draw the peak that would correspond to the hydrogens at C₃ in the molecule shown. Be sure to indicate the integration and place it at an appropriate chemical shift.

Textbook Question

For the compound shown, produce a table of the shift, integration, and multiplicity of each peak you would expect to see in a ¹H NMR spectrum.

Multiple Choice

PRACTICE: Which of the following molecules gives a 1H NMR spectrum consisting of three peaks with integral ratio of 3:1:6 (when signals are counted from left to right)?

Multiple Choice

Which property of a signal contains the number of hydrogen atoms in the set of equivalent hydrogen atoms that caused the signal in a ¹H NMR spectrum?

Textbook Question

For the following molecules, give the integration you would expect for the signal associated with the hydrogens at the labeled carbons. [Pay attention to the symmetry, or lack of symmetry, in the molecules.]

(e)

Textbook Question

(f)

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