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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5:56 minutes

Problem 53

Textbook Question

Each of these four structures has molecular formula C₄H₈O₂. Match the structure with its characteristic proton NMR signals. (Not all of the signals are listed in each case.)

(a) sharp 1H singlet at δ8.0 and 2H triplet at δ4.0
(b) sharp 3H singlet at δ2.0 and 2H quartet at δ4.1
(c) sharp 3H singlet at δ3.7 and 2H quartet at δ2.3
(d) broad 1H singlet at δ11.5 and 2H triplet at δ2.3

Verified step by step guidance

Step 1: Analyze the molecular formula C4H8O2 and recognize that the structures provided are isomers. Each structure corresponds to a different functional group arrangement, which will influence the proton NMR signals.

Step 2: Examine structure (a). It contains a carboxylic acid group (-COOH), which typically produces a broad singlet around δ 11-12 ppm due to the acidic proton. The 2H triplet at δ 2.3 ppm corresponds to the CH2 group adjacent to the carbonyl group.

Step 3: Examine structure (b). It contains an ester functional group (-COOCH3). The sharp 3H singlet at δ 2.0 ppm corresponds to the methyl group directly attached to the oxygen atom. The 2H quartet at δ 4.1 ppm corresponds to the CH2 group adjacent to the oxygen atom.

Step 4: Examine structure (c). It contains an ester functional group (-COOCH2CH3). The sharp 3H singlet at δ 3.7 ppm corresponds to the methyl group attached to the oxygen atom. The 2H quartet at δ 2.3 ppm corresponds to the CH2 group adjacent to the carbonyl group.

Step 5: Examine structure (d). It contains a hydroxyl group (-OH) and a ketone group (-COCH3). The broad 1H singlet at δ 11.5 ppm corresponds to the hydroxyl proton. The 2H triplet at δ 2.3 ppm corresponds to the CH2 group adjacent to the ketone group.

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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 in different environments within a molecule, indicated by chemical shifts (δ) in parts per million (ppm). The splitting patterns (singlets, doublets, triplets) reveal the number of neighboring hydrogen atoms, which helps in deducing the molecular structure.

Chemical Shifts

Chemical shifts in NMR spectroscopy refer to the resonant frequency of a nucleus relative to a standard in a magnetic field. They are influenced by the electronic environment surrounding the hydrogen atoms, with electronegative atoms or functional groups causing downfield shifts (higher δ values). Understanding chemical shifts is crucial for identifying functional groups and predicting the behavior of protons in different molecular environments.

Splitting Patterns

Splitting patterns in NMR arise from the interaction of non-equivalent neighboring hydrogen atoms, described by the n+1 rule, where n is the number of neighboring protons. This results in signals appearing as multiplets (singlets, doublets, triplets, etc.), providing insight into the connectivity and arrangement of atoms in a molecule. Recognizing these patterns is essential for interpreting NMR spectra and correlating them with specific molecular structures.

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