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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7:19 minutes

Problem 21a

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>

Verified step by step guidance

Step 1: Analyze the molecular formula C₄H₁₀O₂. This indicates the presence of 4 carbons, 10 hydrogens, and 2 oxygen atoms. The molecule could be an ether or alcohol, as these functional groups commonly contain oxygen atoms.

Step 2: Examine the NMR spectrum. Peaks around δ1.65 and δ3.75 show complex splitting patterns. This suggests that the protons responsible for these signals are experiencing coupling with multiple neighboring protons, leading to intricate splitting.

Step 3: Consider the peak at δ1.65. This region typically corresponds to protons on carbons adjacent to other functional groups, such as alcohols or ethers. The complex splitting indicates coupling with protons on nearby carbons, possibly in a branched structure.

Step 4: Examine the peak at δ3.75. This region is characteristic of protons on carbons directly bonded to oxygen atoms (e.g., in ethers or alcohols). The complex splitting suggests coupling with protons on adjacent carbons, which could be part of a chain or branch.

Step 5: Propose a structure consistent with the molecular formula and NMR data. A plausible structure is a branched ether or alcohol, such as 2-methoxypropane or 2,2-dimethoxypropane. These structures align with the observed splitting patterns and chemical shifts.

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Key Concepts

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

Nuclear Magnetic Resonance (NMR) Spectroscopy

NMR spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. It relies on the magnetic properties of certain nuclei, primarily hydrogen (1H) and carbon (13C), to provide information about the number of hydrogen atoms, their environment, and how they are connected. The chemical shift (δ) indicates the electronic environment of the nuclei, while the splitting patterns reveal the number of neighboring hydrogen atoms.

Multiplet Splitting in NMR

In NMR, peaks can appear as multiplets due to the interaction of a nucleus with neighboring nuclei, a phenomenon known as spin-spin coupling. The complexity of the splitting pattern depends on the number of adjacent hydrogen atoms and their arrangement. Clean multiplets indicate simple coupling, while complex splitting suggests multiple interactions, often due to overlapping signals from different types of protons or conformational changes in the molecule.

Chemical Environment and Peak Integration

The chemical environment of protons affects their resonance frequency, leading to distinct peaks in an NMR spectrum. Peaks at different δ values correspond to protons in different electronic environments, influenced by factors like electronegativity and hybridization. Peak integration provides quantitative information about the number of protons contributing to each signal, which is essential for deducing the molecular formula and structure of the compound.

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Guided course

06:46

1H NMR Integration

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Related Practice

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.