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

Previous problemNext problem

5:35 minutes

Problem 24b

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>

Verified step by step guidance

Analyze the molecular formula C8H8O provided in the problem. This indicates the molecule contains 8 carbons, 8 hydrogens, and 1 oxygen. The degree of unsaturation can be calculated using the formula: Degree of Unsaturation = (2C + 2 - H)/2. For C8H8O, the degree of unsaturation is (2(8) + 2 - 8)/2 = 5, suggesting the presence of rings and/or double bonds.

Examine the proton NMR spectrum. The peaks near δ = 7-8 ppm suggest the presence of aromatic protons, which are characteristic of benzene rings. This aligns with the degree of unsaturation calculation, indicating an aromatic ring.

The peak near δ = 2.8-3.1 ppm is a multiplet, which suggests the presence of protons adjacent to a functional group, such as a carbonyl group or an aromatic ring. This region is typical for benzylic protons (protons attached to a carbon adjacent to an aromatic ring).

The peak near δ = 9-10 ppm is a singlet, which is characteristic of an aldehyde proton (-CHO group). This strongly suggests the molecule contains an aldehyde functional group.

Combine the observations: The molecule likely contains a benzene ring (aromatic protons), a benzylic group (multiplet near δ = 2.8-3.1 ppm), and an aldehyde group (singlet near δ = 9-10 ppm). Based on the molecular formula and NMR data, propose a structure consistent with these features, such as benzaldehyde (C6H5CHO).

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

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 in a molecule and their environment, allowing chemists to infer connectivity and functional groups. The chemical shifts, splitting patterns, and integration of peaks in the spectrum are key to interpreting the molecular structure.

Chemical Shift

Chemical shift refers to the resonance frequency of a nucleus relative to a standard in a magnetic field, typically measured in parts per million (ppm). In proton NMR, different chemical environments of hydrogen atoms lead to distinct chemical shifts, which help identify functional groups and the electronic environment surrounding the protons. Understanding chemical shifts is crucial for deducing the structure of the compound from the NMR spectrum.

Spin-Spin Coupling

Spin-spin coupling, or J-coupling, occurs when protons that are close to each other influence each other's magnetic environments, resulting in splitting of NMR signals. This phenomenon provides information about the number of neighboring protons and their arrangement, which is essential for constructing the molecular structure. Analyzing the splitting patterns allows chemists to deduce connectivity and confirm the proposed structure.

Recommended video:

Guided course

02:54

Sonogashira Coupling Reaction

Previous problemNext problem

Related Practice

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

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.

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

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>

Textbook Question

Draw the NMR spectra you expect for the following compounds.

(b)

Textbook Question

Draw the NMR spectra you expect for the following compounds.

(a)

Show more practices