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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6:21 minutes

Problem 36

Textbook Question

The following proton NMR spectrum is of a compound of molecular formula C₃H₈O.
<IMAGE>
(a) Propose a structure for this compound.
(b) Assign peaks to show which protons give rise to which signals in the spectrum.

Verified step by step guidance

Step 1: Analyze the molecular formula C3H8O. This formula suggests the compound contains three carbon atoms, eight hydrogen atoms, and one oxygen atom. The degree of unsaturation is zero, indicating no double bonds, triple bonds, or rings are present.

Step 2: Examine the proton NMR spectrum. The spectrum shows multiple peaks at different chemical shifts (δ values). Peaks labeled 'a', 'b', 'c', 'd', and 'e' correspond to different proton environments. The integration of these peaks will help determine the number of protons in each environment.

Step 3: Assign chemical shifts to functional groups. The peak at δ ≈ 4 ppm (labeled 'e') is characteristic of protons attached to a carbon bonded to an oxygen atom (likely a hydroxyl group or an alcohol). The peak at δ ≈ 1 ppm (labeled 'a') corresponds to protons in a methyl group (-CH3). Peaks at δ ≈ 2-3 ppm (labeled 'b', 'c', and 'd') are likely from protons in methylene groups (-CH2-) adjacent to the oxygen atom.

Step 4: Propose a structure based on the molecular formula and NMR data. A plausible structure for C3H8O is isopropanol (CH3CHOHCH3). This structure matches the molecular formula and the expected proton environments: a hydroxyl group (-OH), two methyl groups (-CH3), and one methine group (-CH).

Step 5: Assign peaks to specific protons in the structure. The peak at δ ≈ 4 ppm ('e') corresponds to the hydroxyl proton (-OH). The peak at δ ≈ 1 ppm ('a') corresponds to the protons in the two methyl groups (-CH3). The peaks at δ ≈ 2-3 ppm ('b', 'c', and 'd') correspond to the methine proton (-CH) and the splitting pattern due to coupling with adjacent protons.

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Key Concepts

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

Proton NMR Spectroscopy

Proton Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. It provides information about the number of hydrogen atoms (protons) in a molecule and their environment, allowing chemists to infer connectivity and functional groups. Peaks in the NMR spectrum correspond to different types of protons, with their chemical shifts indicating the electronic environment around them.

Chemical Shift

Chemical shift is a key parameter in NMR spectroscopy that indicates the resonance frequency of a nucleus relative to a standard reference. It is measured in parts per million (ppm) and reflects the electronic environment surrounding the protons. Different functional groups and molecular structures influence the chemical shift, allowing for the identification of specific types of protons in a compound.

Integration and Splitting Patterns

Integration in NMR refers to the area under a peak, which correlates to the number of protons contributing to that signal. Splitting patterns arise from the interaction of neighboring protons, providing insight into the number of adjacent protons (n+1 rule). Understanding these patterns helps in deducing the connectivity and arrangement of protons in the molecular structure, which is crucial for accurately proposing a compound's structure.

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08:06

Common Splitting Patterns

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Related Practice

Textbook Question

Tell precisely how you would use the proton NMR spectra to distinguish between the following pairs of compounds.

(b)

Textbook Question

Tell precisely how you would use the proton NMR spectra to distinguish between the following pairs of compounds.

(a) 1-bromopropane and 2-bromopropane

Textbook Question

Sketch your predictions of the proton NMR spectra of the following compounds.

(b)

Textbook Question

Sketch your predictions of the proton NMR spectra of the following compounds.

(a) CH₃–O–CH₂CH₃

Textbook Question

An unknown compound has the molecular formula C₉H₁₁Br. Its proton NMR spectrum shows the following absorptions:

singlet, δ7.1, integral 44 mm

singlet, δ2.3, integral 130 mm

singlet, δ2.2, integral 67 mm

Propose a structure for this compound.

Textbook Question

Five proton NMR spectra are given here, together with molecular formulas. In each case, propose a structure that is consistent with the spectrum.

(b) <IMAGE>

Textbook Question

Give the spectral assignments for the protons in isobutyl alcohol (Solved Problem 13-4). For example, H^a is a singlet, area = 1, at δ2.4.

Textbook Question

Propose chemical structures consistent with the following NMR spectra and molecular formulas. In spectrum (a), explain why the peaks around δ1.65 and δ3.75 are not clean multiplets, but show complex splitting.

(a) <IMAGE>

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The following proton NMR spectrum is of a compound of molecular formula C3H8O.<IMAGE>(a) Propose a structure for this compound. (b) Assign peaks to show which protons give rise to which signals in the spectrum.

Key Concepts

Proton NMR Spectroscopy

Chemical Shift

Integration and Splitting Patterns

The following proton NMR spectrum is of a compound of molecular formula C₃H₈O.
<IMAGE>
(a) Propose a structure for this compound.
(b) Assign peaks to show which protons give rise to which signals in the spectrum.